MitoPedia: Respirometry

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MitoPedia: Respirometry

MitoPedia - high-resolution terminology - matching measurements at high-resolution.
The MitoPedia terminology is developed continuously in the spirit of Gentle Science.

Additive effect of convergent electron flowAα&βAdditivity describes the princple of substrate control of mitochondrial respiration with convergent electron flow. The additive effect of convergent electron flow is a consequence of electron flow converging at the Q-junction from respiratory Complexes I and II (NS or CI&II e-input). Further additivity may be observed by convergent electron flow through glycerophosphate dehydrogenase and electron-transferring flavoprotein complex. Convergent electron flow corresponds to the operation of the TCA cycle and mitochondrial substrate supply in vivo. Physiological substrate combinations supporting convergent NS e-input are required for reconstitution of intracellular TCA cycle function. Convergent electron flow simultaneously through Complexes I and II into the Q-junction supports higher OXPHOS capacity and ETS capacity than separate electron flow through either CI or CII. The convergent NS effect may be completely or partially additive, suggesting that conventional bioenergetic protocols with mt-preparations have underestimated cellular OXPHOS capacities, due to the gating effect through a single branch. Complete additivity is defined as the condition when the sum of separatly measured respiratory capacities, N + S, is identical to the capacity measured in the state with combined substrates, NS (CI&II). This condition of complete additivity, NS=N+S, would be obtained if electron channeling through supercomplex CI, CIII and CIV does not interact with the pool of redox intermediates in the pathway from CII to CIII and CIV, and if the capacity of the phosphorylation system (≈P) does not limit OXPHOS capacity (excess E-P capacity factor is zero). In most cases, however, additivity is incomplete, NS < N+S.
Air calibrationR1Air calibration of an oxygen sensor (polarographic oxygen sensor) is performed routinely on any day before starting a respirometric experiment. The volume fraction of oxygen in dry air is constant. An aqueous solution in equilibrium with air has the same partial pressure as that in water vapour saturated air. The water vapour is a function of temperature only. The partial oxygen pressure in aqueous solution in equilibrium with air is, therefore, a function of total barometric pressure and temperature. Bubbling an aqueous solution with air generates deviations from barometric pressure within small gas bubbles and is, therefore, not recommended. To equilibrate an aqueous solution ata known partial pressure of oxygen [kPa], the aqueous solution is stirred rigorously in a chamber enclosing air at constant temperature. The concentration of oxygen, cO2 [µM], is obtained at any partial pressure by multiplying the partial pressure by the oxygen solubility, SO2 [µM/kPa]. SO2 is a function of temperature and composition of the salt solution, and is thus a function of the experimental medium. The solubility factor of the medium, FM, expresses the oxygen solubility relative to pure water at any experimental temperature. FM is 0.89 in serum (37 °C) and 0.92 in MiR06 or MiR05 (30 °C and 37 °C).
Barometric pressurepbBarometric pressure, pb, is an important variable to be measured for calibrating oxygen sensors in solutions that are equilibrated with air. The atm-standard pressure (1 atm = 760 mmHg = 101.325 kPa) has been replaced by the standard pressure of 100 kPa. The partial pressure of oxygen, pO2, in air is a function of barometric pressure, which changes with altitude and locally with weather conditions. The partial oxygen pressure declines by 12% to 14% per 1,000 m up to 6,000 m, and by 15% to 17% per 1,000 m between 6,000 and 9,000 m. The O2k-Barometric Pressure Transducer is built into the OROBOROS Oxygraph-2k as a basis for accurate air calibrations in high-resolution respirometry. For highest-level accuracy of calculation of oxygen pressure, it is recommended to compare at regular intervals the barometric pressure recording provided by the O2k with a calibrated barometric pressure recording at an identical time point and identical alitude.
Basal respirationBMRBasal respiration or basal metabolic rate (BMR) is the minimal rate of metabolism required to support basic body functions, essential for maintenance only. BMR (in humans) is measured at rest 12 to 14 hours after eating in a physically and mentally relaxed state at thermally neutral room temperature. Maintenance energy requirements include mainly the metabolic costs of protein turnover and ion homeostasis. In many aerobic organisms, and particularly well studied in mammals, BMR is fully aerobic, i.e. direct calorimetry (measurement of heat dissipation) and indirect calorimetry (measurement of oxygen consumption multiplied by the oxycaloric equivalent) agree within errors of measurement (Blaxter KL 1962. The energy metabolism of ruminants. Hutchinson, London: 332 pp [1]). In many cultured mammalian cells, aerobic glycolysis contributes to total ATP turnover (Gnaiger and Kemp 1990 [2]), and under these conditions, 'respiration' is not equivalent to 'metabolic rate'. Basal respiration in humans and skeletal muscle mitochondrial function (oxygen kinetics) are correlated (Larsen et al 2011 [3]). » MiPNet article
Biochemical threshold effectDue to threshold effects, even a large defect diminishing the velocity of an individual enzyme results in only minor changes of pathway flux.
Calorespirometric ratioCR ratioThe calorimetric/respirometric or calorespirometric ratio (CR ratio) is the ratio of calorimetrically and respirometrically measured heat and oxygen flux, determinded by calorespirometry. The experimental CR ratio is compared with the theoretically derived oxycaloric equivalent, and agreement in the range of -450 to -480 kJ/mol O2 indicates a balanced aerobic energy budget (Gnaiger and Staudigl 1987). In the transition from aerobic to anaerobic metabolism, there is a limiting pO2, plim, below which CR ratios become more exothermic since anaerobic energy flux is switched on.
CalorespirometryCRCalorespirometry is the method of measuring simultaneously metabolic heat flux (calorimetry) and oxygen flux (respirometry). The calorespirometric ratio (CR ratio; heat/oxygen flux ratio) is thus experimentally determined and can be compared with the theoretical oxycaloric equivalent, as a test of the aerobic energy balance.
Cell ergometryBiochemical cell ergometry aims at measurement of JO2max (compare VO2max or VO2peak in exercise ergometry of humans and animals) of cell respiration linked to phosphorylation of ADP to ATP. The corresponding OXPHOS capacity is based on saturating concentrations of ADP, [ADP]*, and inorganic phosphate, [Pi]*, available to the mitochondria. This is metabolically opposite to uncoupling respiration, which yields ETS capacity. The OXPHOS state can be established experimentally by selective permeabilization of cell membranes with maintenance of intact mitochondria, titrations of ADP and Pi to evaluate kinetically saturating conditions, and establishing fuel substrate combinations which reconstitute physiological TCA cycle function. Uncoupler titrations are applied to determine the apparent ETS excess over OXPHOS capacity and to calculate OXPHOS- and ETS coupling efficiencies, j≈P and j≈E. These normalized flux ratios are the basis to calculate the ergometric or ergodynamic efficiency, ε = j · f, where f is the normalized force ratio. » MiPNet article
Cell respirationCell respiration channels metabolic fuels into the chemiosmotic coupling (bioenergetic) machinery of oxidative phosphorylation, being regulated by and regulating oxygen consumption (or consumption of an alternative final electron acceptor) and molecular redox states, ion gradients, mitochondrial (or microbial) membrane potential, the phosphorylation state of the ATP system, and heat dissipation in response to intrinsic and extrinsic energy demands. See also respirometry. In internal or cell respiration in contrast to fermentation, redox balance is maintained by the use of external electron acceptors, transported into the cell from the environment. The chemical potential from electron donors to electron acceptors is converted in the electron transfer system to generate a chemiosmotic potential that in turn drives ATP synthesis.
Chemical background correction of oxygen fluxChemical background correction of oxygen flux is the correction of oxygen flux for the side reaction of autooxidation, as a function of oxygen concentration.
Closed systemA closed system is a system with boundaries that allow external exchange of energy (heat and work), but do not allow exchange of matter. A limiting case is light and electrons which cross the system boundary when work is exchanged in the form of light or electric energy. If the surroundings are maintained at constant temperature, and heat exchange is rapid to prevent the generation of thermal gradients, then the closed system is isothermal. Changes of closed systems can be partitioned according to internal and external sources.
Convergent electron flown.a.
Convergent electron flow
Convergent electron flow is built into the metabolic design of the electron transfer system. The glycolytic pathways are characterized by important divergent branchpoints: phosphoenolpyruvate (PEPCK) branchpoint to pyruvate or oxaloactetate; pyruvate branchpoint to (aerobic) acetyl-CoA or (anaerobic) lactate or alanine. The mitochondrial electron transfer system, in contrast, is characterized by convergent junctions: (1) the N-junction and F-junction in the mitochondrial matrix at ETS level 4, with dehydrogenases (including the TCA cycle) and ß-oxidation generating NADH and FADH2 as substrates for Complex I and electron-transferring flavoprotein complex, respectively, and (2) the Q-junction with inner mt-membrane respiratory complexes at ETS level 3, reducing the oxidized ubiquinone and partially reduced semiquinone to the fully reduced ubiquinol, feeding electrons into Complex III.
Coupled respirationCoupled respiration drives oxidative phosphorylation of the diphosphate ADP to the triphosphate ATP, mediated by proton pumps across the inner mitochondrial membrane. Intrinsically uncoupled respiration, in contrast, does not lead to phosphorylation of ADP, despite of protons being pumped across the inner mt-membrane. Coupled respiration, therefore, is the coupled part of respiratory oxygen flux that pumps the fraction of protons across the inner mt-membrane which is utilized by the phosphorylation system to produce ATP from ADP and Pi. In the OXPHOS state, mitochondria are in a partially coupled state, and the corresponding coupled respiration is the free OXPHOS capacity. In the state of ROUTINE respiration, coupled respiration is the free ROUTINE activity.
Coupling control factorCCFCoupling control factors, CCF, are flux control factors, FCF, at a constant ETS-competent pathway control state.
Coupling control protocolCCPA coupling control protocol, CCP, induces different coupling control states at constant substrate supply. In intact cells, the CCP can be applied by using membrane-permeable inhibitors of the phosphorylation system (e.g. oligomycin) and uncouplers (e.g. CCCP). Coupling control states in intact cells include R, L, E; LEAK, ROUTINE, and ETS. Coupling control states in isolated mitochondria, permeabilized cells or homogenates include L, P, E; LEAK, OXPHOS, and ETS. The term phosphorylation control protocol, PCP, has been introduced synonymous for CCP. » MiPNet article
Coupling control ratioCCRCoupling control ratios, CCR, are flux control ratios, FCR, at a constant mitochondrial substrate control state. In mitochondrial preparations, there are three well-defined coupling states of respiration, L, P, E (LEAK, OXPHOS, ETS). In intact cells, state P cannot be induced, but a ROUTINE state of respiration, R, can be measured. The reference state, Jref, is defined by taking Jref as the maximum flux, i.e. flux in the ETS state, E, such that the lower and upper limits of the CCR are defined as 0.0 and 1.0. Then there are two mitochondrial CCR, L/E and P/E, and two CCR for intact cells, L/E and R/E.
Coupling control stateCCSCoupling control states are defined in mitochondrial preparations (isolated mitochondria, permeabilized cells, permeabilized tissues, homogenates) as LEAK, OXPHOS, and ETS states of respiration (L, P, E) in any pathway control state which is competent for electron transfer. These coupling states are induced by application of specific inhibitors of the phosphorylation system, titration of ADP and uncouplers. In intact cells, the coupling control states are LEAK, ROUTINE, and ETS states of respiration (L, R, E). Coupling control protocols induce these coupling control states sequentially at a constant pathway control state.
Crabtree effectThe Crabtree effect describes the observation that respiration is frequently inhibited when high concentrations of glucose or fructose are added to the culture medium - a phenomenon observed in numerous cell types, particularly in proliferating cells, not only in tumor cells, in bacteria, and yeast. The Pasteur effect (suppression of glycolysis by oygen) is the converse of the Crabtree effect (aerobic glycolysis to lactate or ethanol).
Cytochrome c control factorFCFcThe cytochrome c control factor expresses the control of respiration by externally added cytochrome c, c, as a fractional change of flux from substrate state CHO to CHOc. In this flux control factor (FCFc), CHOc is the reference state with stimulated flux; CHO is the background state with CHO substrates, upon which c is added,
» MiPNet article
Dilution effectDilution of the concentration of a compound or sample in the experimental chamber by a titration of another solution into the chamber.
DithioniteNa2S2O4Zero oxygen solution powder, Na2S2O4, used for calibration of oxygen sensors at zero oxygen, or for stepwise reduction of oxygen concentration in instrumental O2 background tests.
Dyscoupled respirationDyscoupled respiration is LEAK respiration distinguished from intrinsically (physiologically) uncoupled and from extrinsic experimentally uncoupled respiration as an indication of extrinsic uncoupling (pathological, toxicological, pharmacological by agents that are not specifically applied to induce uncoupling, but are tested for their potential dyscoupling effect). Dyscoupling indicates a mitochondrial dysfunction. In addition to intrinsic uncoupling, dyscoupling occurs under pathological and toxicological conditions. Thus a distinction is made between physiological uncoupling and pathologically defective dyscoupling in mitochondrial respiration.
ETS capacityEE.jpg ETS capacity is the respiratory electron transfer system capacity, E, of mitochondria in the experimentally induced noncoupled state. In intact mitochondria, the ETS capacity depends not only on the inner membrane-bound ETS (mETS, with respiratory Complexes CI to CIV, electron-transferring flavoprotein complex ETF, and glycerophosphate dehydrogenase complex) but also integrates transporters across the inner mt-membrane, the TCA cycle and other matrix dehydrogenases. Its experimental determination in mitochondrial preparations or intact cells requires the measurement of oxygen consumption in the presence of defined substrates and of an established uncoupler at optimum concentration. This optimum concentration is determined by stepwise titration of the uncoupler up to the concentration inducing maximum flux as the determinant of ETS capacity. » MiPNet article
ETS coupling efficiencyj≈EETS coupling efficiency The ETS coupling efficiency (E-L coupling control factor) is a normalized flux ratio, j≈E = ≈E/E = (E-L)/E = 1-L/E. j≈E is 0.0 at zero coupling (L=E) and 1.0 at the limit of a fully coupled system (L=0). The background state is the LEAK state which is stimulated to ETS reference state by uncoupler titration. LEAK states LN or LT may be stimulated first by saturating ADP (State P) with subsequent uncoupler titration to State E. The ETS coupling efficiency is based on measurement of a coupling control ratio (LEAK control ratio, L/E), whereas the thermodynamic or ergodynamic efficiency of coupling between ATP production (DT phosphorylation) and oxygen consumption is based on measurement of the output/input flux ratio (~P/O2 ratio) and output/input force ratio (Gibbs force of phosphorylation/Gibbs force of oxidation). Biochemical coupling efficiency is either expressed as the ETS coupling efficiency, j≈E, or OXPHOS coupling efficiency, j≈P, obtained in a coupling control protocol (phosphorylation control protocol). » MiPNet article
Electron flowIeElectron flow through the mitochondrial electron transfer system (ETS) is the scalar component of chemical reactions in oxidative phosphorylation (OXPHOS). Electron flow is most conveniently measured as oxygen consumption (oxygraphic measurement of oxygen flow), with four electrons being taken up when oxygen(02) is reduced to water.
Electron transfer systemETSE.jpg The mitochondrial electron transfer system (ETS; synonymous with 'electron transport system') transfers electrons from externally supplied reduced substrates to oxygen. It consists of the membrane-bound ETS (mETS) with enzyme complexes located in the inner mt-membrane, mt-matrix dehydrogenases generating NADH, and the transport systems involved in metabolite exchange across the mt-membranes (see ETS capacity).
Ergodynamic efficiencyεThe ergodynamic efficiency, ε (compare thermodynamic efficiency), is a power ratio between the output power and the (negative) input power of an energetically coupled process. Since power [W] is the product of a flow and the conjugated thermodynamic force, the ergodynamic efficiency is the product of an output/input flow ratio and the corresponding force ratio. The efficiency is 0.0 in a fully uncoupled system (zero output flow) or at level flow (zero output force). The maximum efficiency of 1.0 can be reached only in a fully (mechanistically) coupled system at the limit of zero flow at ergodynamic equilibrium. The ergodynamic efficiency of coupling between ATP production (DT phosphorylation) and oxygen consumption is the flux ratio of DT phosphorylation flux and oxygen flux (~P/O2 ratio) multiplied by the corresponding force ratio. Compare with the OXPHOS coupling efficiency.
Extensive quantityExtensive quantities pertain to a total system, e.g. oxygen flow.
External flowIextExternal flows across the system boundaries are formally reversible. Their irreversible facet is accounted for internally as transformations in a heterogenous system (internal flows, Iint).
The F-junction is a junction for convergent electron flow in the electron transfer system (ETS) from fatty acids through fatty acyl CoA dehydrogenase (reduced form FADH2) to electron transferring flavoprotein (CETF), and further transfer through the Q-junction to Complex III (CIII). The concept of the F-junction and N-junction provides a basis for defining categories of SUIT protocols. Fatty acid oxidation, in the F-pathway control state, not only depends on electron transfer through the F-junction (which is typically rate-limiting) but simultaneously generates NADH and thus depends on N-junction throughput. Hence FAO can be inhibited completely by inhibition of Complex I (CI). In addition and independent of this source of NADH, the N-junction substrate malate is required as a co-substrate for FAO in mt-preparations, since accumulation of AcetylCoA inhibits FAO in the absence of malate. Malate is oxidized in a reaction catalyzed by malate dehydrogenase to oxaloacetate (yielding NADH), which then stimulates the entry of AcetylCoA into the TCA cycle catalyzed by citrate synthase.
Fatty acid oxidationFAOFatty acid oxidation (β-oxidation) is a multi-step process by which fatty acids are broken down to generate acetyl-CoA, NADH and FADH2 for further energy production. Fatty acids (short chain with 4–8, medium-chain with 6–12, long chain with 14-22 carbon atoms) are activated by fatty acyl-CoA synthases (thiokinases) in the cytosol. The outer mt-membrane enzyme carnitine palmitoyltransferase I (CPT 1) generates an acyl-carnitine intermediate for transport into the mt-matrix. Octanoate, but not palmitate, (eight- and 16-carbon saturated fatty acids) may pass the mt-membranes, but both are frequently supplied to mt-preparations in the activated form of octanoylcarnitine or palmitoylcarnitine. Electron-transferring flavoprotein complex (CETF) is located on the matrix face of the inner mt-membrane, and supplies electrons from fatty acid β-oxidation (FAO) to CoQ. FAO cannot proceed without a substrate combination of fatty acids & malate, and inhibition of CI blocks FAO completely. Fatty acids are split stepwise into two carbon fragments forming acetyl-CoA, which enters the TCA cycle by condensation with oxaloacetate (CS reaction). Therefore, FAO implies simultaneous electron transfer into the Q-junction through CETF and CI.
Flux / SlopeJFlux / Slope is the pull-down menu in DatLab for (1) normalization of flux (chamber volume-specific flux, sample-specific flux or flow, or flux control ratios), (2) flux baseline correction, (3) background correction, and (4) flux smoothing, selection of the scaling factor, and stoichiometric normalization using a stoichiometric coefficient. For each signal channel, the signal for the measured substance X is typically calibrated as an amount of substance concentration, cX [µM = nmol/ml]. The signal of the potentiometric channel, however, is primarily expressed logarithmically as pX=-logcX and then transformed to cX. The slope is calculated as the change of concentration over time, dcX/dt [nmol/(s · ml)]. In a chemical reaction, the change of substance X is stoichiometrically related to the changes of all other substrates and products involved in the reaction. If the stoichiometry of the reaction is normalized for substance X, then its stoichiometric coefficient is unity and νX equals 1 if the substance is a product formed in the reaction, but νX equals -1 if the substance is a substrate consumed in the reaction. Oxygen is formed in photosynthesis and νX=1 when expressing photosynthesis as oxygen flux. Oxyygen is consumed in aerobic respiration and νX=-1 when expressing respiration as oxygen flux.
Flux baseline correctionbcFlux baseline correction provides the option to display the plot and all values of the flux (or flow, or flux control ratio) as the total flux, J, minus a baseline flux, J0.
JV(bc) = JV - JV0
JV = (dc/dt) · ν-1 · SF - V
For the oxygen channel, JV is O2 flux per volume [pmol/(s·ml)] (or volume-specific O2 flux), c is the oxygen conentration [nmol/ml = µmol/l = µM], dc/dt is the (positive) slope of oxygen concentration over time [nmol/(s · ml)], ν-1 = -1 is the stoichiometric coefficient for the reaction of oxygen consumption (oxygen is removed in the chemical reaction, thus the stoichiometric coefficient is negative, expressing oxygen flux as the negative slope), SF=1,000 is the scaling factor (converting units for the amount of oxygen from nmol to pmol), and V is the volume-specific background oxygen flux (background correction). Further details: Flux / Slope.
Flux control factorFCFFlux control factors express the control of respiration by a metabolic control variable, X, as a fractional change of flux from YX to ZX, normalized for ZX. ZX is the reference state with high (stimulated or un-inhibited) flux; YX is the background state at low flux, upon which X acts.
jX = (ZX-YX)/ZX = 1-YX/ZX

Complementary to the concept of flux control ratios and analogous to elasticities of metabolic control analysis, the flux control factor of X upon background YX is expressed as the change of flux from YX to ZX normalized for the reference state ZX.

» MiPNet article
Flux control ratioFCRFlux control ratios (FCR), are ratios of oxygen flux in different respiratory control states, normalized for maximum flux in a common reference state, to obtain theoretical lower and upper limits of 0.0 and 1.0 (0% and 100%). For a given protocol or set of respiratory protocols, flux control ratios provide a fingerprint of coupling and substrate control independent of (i) mt-content in cells or tissues, (ii) purification in preparations of isolated mitochondria, and (iii) assay conditions for determination of tissue mass or mt-markers external to a respiratory protocol (CS, protein, stereology, etc.). FCR obtained from a single respirometric incubation with sequential titrations (sequential protocol; SUIT protocol) provide an internal normalization, expressing respiratory control independent of mitochondrial content and thus independent of a marker for mitochondrial amount. FCR obtained from separate (parallel) protocols depend on equal distribution of subsamples obtained from a homogenous mt-preparation or determination of a common mitochondrial marker.
Instrumental background oxygen fluxJ°O2Instrumental background oxygen flux, J°O2, in a respirometer is due to oxygen consumption by the POS, and oxygen diffusion into or out of the aqueous medium in the O2k-Chamber. It is a property of the instrumental system, measured in the range of experimental oxygen levels by a standardized instrumental background test. The oxygen regime from air saturation towards zero oxygen is applied generally in experiments with isolated mitochondria and intact or permeabilized cells. To overcome oxygen diffusion limitation in permeabilized fibres and homogenates, an elevated oxygen regime is applied, requiring instrumental background test in the same range of elevated oxygen.

Instrumental background correction eliminates errors by systemic flux compensation, automatically performed by DatLab.

Automatic correction for the instrumental background oxygen flux is an essential standard in high resolution respirometry. At the same time an instrumental background experiment is the ultimate test for instrumental performance, evaluating chamber performance after completion of all elements of the Oxygen sensor test. The instrumental background oxygen flux measured at air saturation should reflect the theoretically predicted volume-specific oxygen consumption by the oxygen sensor. The actual agreement using experimental respiration medium provides at the same time a test that excludes microbial contamination of the medium or serves to evaluate any autoxidation processes in newly tested experimental media.
Intact cellsceIntact cells (ce) are characterized by an intact cell membrane. Cell viability should be >95% for various experimental investigations, including cell respirometry. In contrast, the cell membrane of intact cells can be permeabilized selectively by mild detergents (digitonin), to obtain the mt-preparation of permeabilized cells used for cell ergometry.
Internal flowIintWithin the system boundaries, irreversible internal flows of heat and matter along gradients or internal transformations (chemical reactions) contribute to the internal entropy production, dintS.
International oxygraph courseIOCInternational Oxygraph Course (IOC), see O2k-Workshops.
L/P coupling control ratioL/PL/P coupling control ratio The L/P coupling control ratio or LEAK/OXPHOS coupling control ratio combines the effects of coupling (L/E) and limitation by the phosphorylation system (P/E); L/P = (L/E) / (P/E) = 1/RCR.
LEAK control ratioL/ELEAK control ratio The LEAK control ratio, or L/E coupling control ratio [1,2], is the flux ratio of LEAK respiration over ETS capacity, as determined by measurement of oxygen consumption in sequentially induced states L and E of respiration. The ETS control ratio is an index of uncoupling or dyscoupling at constant ETS capacity. L/E increases with uncoupling from a theoretical minimum of 0.0 for a fully coupled system, to 1.0 for a fully uncoupled system [3].
LEAK respirationLL.jpg LEAK respiration or LEAK oxygen flux, L, compensating for proton leak, proton slip, cation cycling and electron leak, is a dissipative component of respiration which is not available for performing biochemical work and thus related to heat production. LEAK respiration is measured in the LEAK state, in the presence of reducing substrate(s), but absence of ADP (theoretically, absence of inorganic phosphate presents an alternative), or after enzymatic inhibition of the phosphorylation system. The LEAK state is the non-phosphorylating resting state of intrinsic uncoupled or dyscoupled respiration when oxygen flux is maintained mainly to compensate for the proton leak at a high chemiosmotic potential, when ATP synthase is not active. In this non-phosphorylating resting state, the electrochemical proton gradient is increased to a maximum, exerting feedback control by depressing oxygen flux to a level determined mainly by the proton leak and the H+/O2 ratio. In this state of maximum protonmotive force, LEAK respiration is higher than the LEAK component in state P (OXPHOS capacity). The conditions for measurement and expression of respiration vary (oxygen flux in state L, JO2L or oxygen flow in state L, IO2L). If these conditions are defined and remain consistent within a given context, then the simple symbol L for respiratory state can be used as a substitute for the more explicit expression for respiratory activity. » MiPNet article
Limiting pO2plimIn the transition from aerobic to anaerobic metabolism, there is a limiting pO2, plim, below which anaerobic energy flux is switched on and CR ratios become more exothermic than the oxycaloric equivalent. plim may be significanlty below the critical pO2.
LinearityLinearity is the ability of the method to produce test results that are proportional, either directly or by a well-defined mathematical transformation, to the concentration of the analyte in samples within a given range. This property is inherent in the Beer-Lambert law for absorbance alone, but deviations occur in scattering media. It is also a property of fluorescence, but a fluorophore may not exhibit linearity, particularly over a large range of concentrations.
Malate-aspartate shuttleThe malate-aspartate shuttle involves the glutamate-aspartate carrier and the 2-oxoglutarate carrier exchanging malate2- for 2-oxoglutarate2-. Cytosolic and mitochondrial malate dehydrogenase and transaminase complete the shuttle for the transport of cytosolic NADH into the mitochondrial matrix. It is most important in heart, liver and kidney.
MicroplatesMicroplate readers allow large numbers of sample reactions to be assayed in well format microtitre plates. The most common microplate format used in academic research laboratories or clinical diagnostic laboratories is 96-well (8 by 12 matrix) with a typical reaction volume between 100 and 200 µL per well. a wide range of applications involve the use of fluorescence measurements , although they can also be used in conjunction with absorbance measurements.
Mitochondrial markermt-markerMitochondrial markers are structural or functional properties that are specific for mitochondria. A structural mt-marker is the area of the inner mt-membrane or mt-volume determined stereologically, which has its limitations due to different states of swelling. If mt-area is determined by electron microscopy, the statistical challenge has to be met to convert area into a volume. When fluorescent dyes are used as mt-marker, distinction is necessary between mt-membrane potential dependent and independent dyes. mtDNA or cardiolipin content may be considered as a mt-marker. Mitochondrial marker enzymes may be determined as molecular (amount of protein) or functional properties (enzyme activities). Respiratory capacity in a defined respiratory state of a mt-preparation can be considered as a functional mt-marker, in which case respiration in other respiratory states is expressed as flux control ratios. » MiPNet article
Mitochondrial membrane potentialmtMP, ΔψmtThe mitochondrial membrane potential, mtMP, is the electric part of the protonmotive force, Δpmt.

Δψmt = Δpmt - ΔµH+ / F

mtMP or Δψmt is the potential difference across the inner mitochondrial (mt) membrane, expressed in the electric unit of volt [V]. Electric force of the mitochondrial membrane potential is the electric energy change per ‘motive’ electron or per electron moved across the transmembrane potential difference, with the number of ‘motive’ electrons expressed in the unit coulomb [C].

The chemical part of the protonmotive force, µH+ / F stems from the difference of pH across the mt-membrane. It contains a factor that bridges the gap between the electric force [J/C] and the chemical force [J/mol]. This factor is the Faraday constant, F, for conversion between electric force expressed in joules per coulomb or Volt [V=J/C] and chemical force with the unit joules per mole or Jol [Jol=J/mol],

F = 96.4853 kJol/V = 96,485.3 C/mol
Mitochondrial respirationIntegrative measure of the dynamics of complex coupled metabolic pathways, including metabolite transport across the mt-membranes, TCA cycle function with electron transfer through dehydrogenases in the mt-matrix, membrane-bound electron transfer mETS, the transmembrane proton circuit, and the phosphorylation system.
The N-junction is a junction for convergent electron flow in the electron transfer system (ETS) from type N substrates (further details »N-pathway control state) through the mt-NADH pool to Complex I (CI), and further transfer through the Q-junction to Complex III (CIII). Representative type N substrates are pyruvate (P), glutamate (G) and malate (M). The corresponding dehydrogenases (PDH, GDH, MDH) and some additional TCA cycle dehydrogenases (isocitrate dehydrogenase, oxoglutarate dehydrogenase generate NADH, the substrate of Complex I (CI). The concept of the N-junction and F-junction provides a basis for defining categories of SUIT protocols based on pathway control states.
NADH pathway control stateN
The NADH pathway control state (N) is obtained by addition of NADH-linked substrates (CI-linked), feeding electrons into the N-junction catalyzed by various mt-dehydrogenases. N-supported flux is induced in mt-preparations by addition of NADH-generating substrate combinations of pyruvate (P), glutamate (G), malate (M), oxaloacetate (Oa), oxoglutarate (Og), citrate, hydroxybutyrate. These N-junction substrates are (indirectly) linked to Complex I by the corresponding dehydrogenase-catalyzed reactions reducing NAD+ to NADH+H+. The most commonly applied N-junction substrate combinations are: PM, GM, PGM. The malate anaplerotic pathway control state (M alone) is a special case related to malic enzyme (mtME). The glutamate anaplerotic pathway control state (aN; G alone) supports respiration through glutamate dehydrogenase (mtGDH). In mt-preparations, succinate dehydrogenase (SDH; CII) is largely substrate-limited in N-linked respiration, due to metabolite depletion into the incubation medium. The residual involvement of S-linked respiration in the N-pathway control state can be further suppressed by the CII-inhibitor malonic acid). In the N-pathway control state ETS pathway level 4 is active.
NS-S control factorjNS-SThe NS-S control factor (CI&II-CII substrate control factor) expresses the relative stimulation of succinate supported respiration (S) by NADH-linked substrates (N), with the S-pathway control state as the background state and the NS-pathway control state as the reference state. In typical SUIT protocols with type N and S substrates, flux in the NS-pathway control state, NS, is inhibited by Rotenone to measure flux in the S-pathway control state, SRot or S. Then the NS-S control factor is
jNS-S = (NS-S)/NS
The NS-S control factor expresses the fractional change of flux in a defined coupling control state when inhibition by rotenone is removed from flux under S-pathway control in the presence of a type N substrate combination. Experimentally rotenone (Rot) is added to the NS-state. The reversed protocol, adding N-substrates to a S-pathway control background does not provide a valid estimation of S-respiration with succinate in the absence of Rot, since oxaloacetate accumulates as a potent inhibitor of succinate dehydrogenase (CII).
NoiseIn fluorometry and spectrophotometry, noise can be attributed to the statistical nature of the photon emission from a light source and the inherent noise in the instrument’s electronics. The former causes problems in measurements involving samples of analytes with a low extinction coefficient and present only in low concentrations. The latter becomes problematic with high absorbance samples where the light intensity emerging from the sample is very small.
Noncoupled respirationEE.jpg Noncoupled respiration is distinguished from general (pharmacological or mechanical) uncoupled respiration, to give a label to an effort to reach the state of maximum uncoupler-activated respiration without inhibiting respiration. Noncoupled respiration, therefore, yields an estimate of ETS capacity. Experimentally uncoupled respiration may fail to yield an estimate of ETS capacity, due to inhibition of respiration above optimum uncoupler concentrations or insufficient stimulation by sub-optimal uncoupler concentrations. Optimum uncoupler concentrations for evaluation of (noncoupled) ETS capacity require inhibitor titrations (Steinlechner-Maran 1996 Am J Physiol Cell Physiol; Huetter 2004 Biochem J; Gnaiger 2008 POS). Noncoupled respiration is maximum electron flow in an open-transmembrane proton circuit mode of operation (see ETS capacity).
Nuclear respiratory factor 1NRF-1Nuclear respiratory factor 1 is a transcription factor downstream of PGC-1alpha involved in coordinated expression of nDNA and mtDNA.
O2kO2kO2k - OROBOROS Oxygraph-2k: the modular system for high-resolution respirometry.
O2k high-resolution respirometryHRR
Mitochondria and cell research has been advanced by numerous applications of O2k high-resolution respirometry (HRR). HRR is based on the OROBOROS O2k, combining chamber design, application of oxygen-tight materials, electrochemical and optical sensors, Peltier-temperature control and software features (DatLab) to obtain the unique sensitive and quantitative resolution of oxygen concentration and oxygen flux, with a closed-chamber or open-chamber mode of operation (TIP2k). Standardized calibration of the polarographic oxygen sensor (static sensor calibration), calibration of the sensor response time (dynamic sensor calibration), and evaluation of instrumental background oxygen flux (systemic flux compensation) provide the experimental basis for high accuracy of quantitative results and quality control in HRR. The most important extension to O2k-MultiSensor systems is the O2k-Fluorometer.
O2k-FluorometerO2k-Fluorometer (OROBOROS O2k-Fluorometer, OROBOROS Oxygraph-2k Fluorometer) - the experimental system complete for high-resolution respirometry (HRR) combined with fluorometry. The O2k-Fluorometer includes the O2k-Core, O2k-Fluo LED2-Module and TIP2k, and supports all other add-on O2k-Modules of the Oxygraph-2k. The O2k is a sole source apparatus with no other instruments meeting its specifications.
OXPHOS capacityPP.jpg OXPHOS capacity (P) is the respiratory capacity of mitochondria in the ADP-activated state of oxidative phosphorylation, at saturating concentrations of ADP (possibly in contrast to State 3), inorganic phosphate, oxygen, and defined reduced substrates. » MiPNet article
OXPHOS control ratioP/EOXPHOS control ratio The OXPHOS control ratio or P/E coupling control ratio (OXPHOS/ETS; phosphorylation system control ratio) is an expression of the limitation of OXPHOS capacity by the phosphorylation system. The relative limitation of

OXPHOS capacity by the capacity of the phosphorylation system is better expressed by the excess E-P capacity factor, jExP = 1-P/E. The P/E ratio increases with increasing capacity of the phosphorylation system up to a maximum of 1.0 when it matches or is in excess of ETS capacity. P/E also increases with uncoupling. P/E increases from the lower boundary set by L/E (zero capacity of the phosphorylation system), to the upper limit of 1.0, when there is no limitation of P by the phosphorylation system or the proton backpressure (capacity of the phosphorylation system fully matches the ETS capacity; or if the system is fully uncoupled). It is important to separate the kinetic effect of ADP limitation from limitation by enzymatic capacity at saturating ADP concentration.

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OXPHOS coupling efficiencyj≈POXPHOS coupling efficiency The OXPHOS coupling efficiency (P-L or ≈P control factor), j≈P = ≈P/P = (P-L)/P = 1-L/P. OXPHOS capacity corrected for LEAK respiration is the free OXPHOS capacity, ≈P = P-L. The OXPHOS coupling efficiency is the ratio of free to total OXPHOS capacity. j≈P = 1.0 for a fully coupled system (when RCR approaches infinity); j≈P = 0.0 (RCR=1) for a system with zero respiratory phosphorylation capacity (≈P=0) or zero ETS coupling efficiency (E-L=0 when L=P=E). If State 3 is measured at saturating ADP and Pi concentrations (State 3 = P), then the respiratory acceptor control ratio, RCR, is P/L. Under these conditions, the RCR and OXPHOS coupling efficiency are related by a hyperbolic function, j≈P = 1-RCR-1. » MiPNet article
OctanoateOcaOctanoate (octanoic acid). C8H16O2 Common name: Caprylic acid.
Open systemAn open system is a system with boundaries that allow external exchange of energy and matter; the surroundings are merely considered as a source or sink for quantities transferred across the system boundaries (external flows, Iext).
Oxidative phosphorylationOXPHOSP.jpg Oxidative phosphorylation (OXPHOS) is the oxidation of reduced fuel substrates by electron transfer to oxygen, chemiosmotically coupled to the phosphorylation of ADP to ATP and accompanied by an intrinsically uncoupled component of respiration. The OXPHOS state (P) of respiration provides a measure of OXPHOS capacity, which is frequently corrected for residual oxygen consumption (ROX).
Oxycaloric equivalentDeltakHO2The oxycaloric equivalent is the theoretically derived enthalpy change of the oxidative catabolic reactions per amount of oxygen respired, DeltakHO2, ranging from -430 to -480 kJ/mol O2. The oxycaloric equivalent is used in indirect calorimetry to calculate the theoretically expected metabolic heat flux from the respirometrically measured metabolic oxygen flux. Calorimetric/respirometric ratios (CR ratios; heat/oxygen flux ratios) are experimentally determined by calorespirometry. A CR ratio more exothermic than the oxycaloric equivalent of -480 kJ/mol indicates the simultaneous involvement of aerobic and anaerobic mechanisms of energy metabolism.
Oxygen flowIO2Respiratory oxygen flow is the oxygen consumption per total system, extensive quantity. Flow is advancement of a transformation in a system per time. Oxygen flow of a cell, or respiration per million cells, is distinguished from oxygen flux (e.g. per mg protein or wet weight).
Oxygen fluxJO2Oxygen flux, JO2, is a specific quantity. Oxygen flux is oxygen flow, IO2 [mol·s-1 per system], divided by system size. Flux may be volume-specific (flow per volume [pmol·s-1·ml-1]), mass-specific (flow per mass [pmol·s-1·mg-1]), or marker-specific (e.g. flow per mtDNA). Oxygen flux (e.g. per body mass, or per cell mass) is distinguished from oxygen flow (per subject, or per million cells).
Oxygen kineticsOxygen kinetics describes the dependence of respiration of isolated mitochondria or cells on oxygen partial pressure. Frequently, a strictly hyperbolic kinetics is observed, with two parameters, the oxygen pressure at half-maximum flux, p50, and maximum flux, Jmax. The p50 is in the range of 0.2 to 0.8 kPa for cytochrome c oxidase, isolated mitochondria and small cells, strongly dependent on Jmax and coupling state.
Oxygen pressurepO2Oxygen pressure or partial pressure of oxygen [kPa], related to oxygen concentration in solution by the oxygen solubility, SO2 [µM/kPa].
Oxygen pressure, intracellularpO2,iPhysiological, intracellular oxygen pressure is significantly lower than air saturation under normoxia, hence respiratory measurements carried out at air saturation are effectively hyperoxic for cultured cells and isolated mitochondria.
Oxygen solubilitySO2The oxygen solubility, SO2 [µM/kPa], expresses the oxygen concentration in solution in equilibrium with the oxygen pressure in a gas phase, as a function of temperature and composition of the solution. SO2 is 10.56 µM/kPa in pure water at 37 °C. At standard barometric pressure (100 kPa), the oxygen concentration at air saturation is 207.3 µM at 37 °C (19.6 kPa partial oxygen pressure). In MiR06 and serum, the corresponding saturation concentrations are 191 and 184 µM. The oxygen solubility depends on temperatue and the concentrations of solutes in solution. See also: Oxygen solubility factor
P50p50p50 is the oxygen partial pressure at which (a) respiratory flux is 50% of maximum oxygen flux, Jmax, at saturating oxygen levels. The oxygen affinity is indirectly proportional to the p50. The p50 depends on metabolic state and rate. (b) p50 is the oxygen partial pressure at which oxygen binding (on myoglobin, haemoglobin) is 50%, or desaturation is 50%.
POS calibration - dynamicCalibration of the sensor response time. See also POS calibration - static.
POS calibration - staticF5Two-point calibration of the polarographic oxygen sensor, comprising Air calibration and Zero calibration. See also POS calibration - dynamic.
Pathway control ratioSCRSubstrate control ratios, SCR, are flux control ratios, FCR, at a constant mitochondrial coupling control state. Whereas there are only three well-defined coupling control states of mitochondrial respiration, L, P, E (LEAK, OXPHOS, ETS), numerous pathway control states are possible. Careful selection of the reference state, Jref, is required, for which some guidelines may be provided without the possibility to formulate general rules. FCR are best defined by taking Jref as the maximum flux (e.g. NSE), such that flux in various other respiratory states, Ji, is smaller or equal to Jref. However, this is not generally possible with SCR. For instance, the N/S substrate control ratio (at constant coupling control state) may be larger or smaller than 1.0, depending on the mitochondrial source and various mitochondrial injuries. The S-pathway control state may be selected preferentially as Jref, if mitochondria with variable N-linked injuries are studied. In contrast, the reference state, Z, is strictly defined for flux control factors.
Pathway control statePCS, mtPCS
SUIT-catg FNSGpCIV.jpg

Pathway control states (synonymous with ETS substrate control states) are obtained in mitochondrial preparations (isolated mitochondria, permeabilized cells, permeabilized tissues, tissue homogenate) by depletion of endogenous substrates and addition to the mitochondrial respiration medium of fuel substrates (CHNO) activating specific mitochondrial pathways. Mitochondrial pathway control states, mtPCS, have to be defined complementary to mitochondrial coupling control states. Coupling states (LEAK, OXPHOS, ETS) require electron transfer system competent substrate control states, including oxygen supply. Categories of SUIT protocols are defined according to mitochondrial pathway control states.

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Phosphorylation control ratio≈P/EThe phosphorylation control ratio (≈P control ratio), ≈P/E = (P-L)/E, expresses OXPHOS capacity corrected for LEAK respiration (≈P = P-L) as a fraction of ETS capacity. ≈P/E remains constant, if dyscoupling is fully compensated by an increase of OXPHOS capacity and respiratory phosphorylation capacity, ≈P, is maintained constant.
Physiological pathway control stateSee Pathway control state.
Polarographic oxygen sensorPOSPolarographic oxygen sensors (POS) are operated with a polarization voltage between the cathode and anode, connected by an electrolyte. Cathode, anode and electrolyte are separated from the analyte by an oxygen-permeable membrane. Oxygen is reduced at the cathode such that the local oxygen concentration is maintained at zero, and diffuses along the concentration gradient from the stirred medium to the cathode, resulting in a linear calibration between oxygen partial pressure and electric current [Amp] (amperometric mode of operation). The OroboPOS is the POS applied in the OROBOROS O2k.
Polyether ether ketonePEEKPolyether ether ketone (PEEK) is a semicrystalline organic polymer thermoplastic, which is chemically very resistant, with excellent mechanical properties. PEEK is compatible with ultra-high vacuum applications, and its resistance against oxygen diffusion make it an ideal material for high-resolution respirometry (POS insulation; coating of stirrer bars; stoppers for closing the O2k-Chamber).
Polyvinylidene fluoridePVDFPolyvinylidene fluoride (PVDF) is a pure thermoplastic fluoropolymer, which is chemically very resistant, with excellent mechanical properties. It is used generally in applications requiring the highest purity, strength, and resistance to solvents, acids, bases and heat (Wikipedia). PVDF is resistant against oxygen diffusion which makes it an ideal material for high-resolution respirometry (coating of stirrer bars; stoppers for closing the O2k-Chamber).
Power O2k-FluorometerPower O2k-Fluorometer (OROBOROS Power O2k-Fluorometer) - Optional configuration as additional system for increasing output in high-resolution respirometry (HRR) combined with fluorometry. The Power O2k-Fluorometer includes the Power-O2k Core-Unit, O2k-Fluo LED2-Module and TIP2k, and supports all other add-on O2k-Modules of the Oxygraph-2k. It can be added to an existing O2k-Core or O2k-Fluorometer. This application does not require an additional ISS-Integrated Suction System, an O2k-Titration Set and the O2k-Manual. Furthermore, the following OroboPOS Service Tools can be used from the available O2k-Core and are not included: OroboPOS-Mounting Tool, OroboPOS-Polishing Cloth, OroboPOS-Polishing Powder and Pen-Contact Oil. The O2k is a sole source apparatus with no other instruments meeting its specifications.
Proton leakFlux of protons along the electrochemical proton gradient across the inner mt-membrane, contributing to LEAK respiration.
Proton pumpMitochondrial proton pumps are large enzyme complexes (CI, CII, CIV, CV) spanning the inner mt-membrane, partially encoded by mtDNA. CI, CII and CIV are proton pumps that drive protons against the electrochemical proton motive force, driven by electron transfer from reduced substrates to oxygen. In contrast, CV is a proton pump that utilizes the energy of proton flow along the proton motive force to drive phosphorylation of ADP to ATP.
Proton slipProton slip is a property of the proton pumps (Complexes CI, CIII, and CIV) when the proton slips back to the matrix side within the proton pumping process. Slip is different from the proton leak, which depends on Δp and is a property of the inner mt-membrane (including the boundaries between membrane-spanning proteins and the lipid phase). Slip is an uncoupling process that depends mainly on flux and contributes to a reduction in the biochemical coupling efficiency of ATP production and oxygen consumption. Together with proton leak and cation cycling, proton slip is compensated for by LEAK respiration or LEAK oxygen flux, L.
The Q-junction is a junction for convergent electron flow in the electron transfer system (ETS) from type N substrates and mt-matix dehydrogenases through Complex I (CI), from type F substrates and FA oxidation through electron-transferring flavoprotein complex (CETF), from succinate (S) through Complex II (CII), from glycoreophosphate (Gp) through glycerophosphate dehydrogenase complex (CGpDH), from choline through choline dehydrogenase, from dihydro-orotate through dihydro-orotate dehydrogenase, and other enzyme complexes into the Q-cycle (ubiquinol/ubiquinone), and further downstream to Complex III (CIII) and CIV. The concept of the Q-junction, with the N-junction and F-junction upstream, provides the rationale for defining pathway control states and categories of SUIT protocols.
ROUTINE respirationRR.jpg In the intact cell, ROUTINE respiration or ROUTINE activity in the physiological coupling state R, is controlled by cellular energy demand, energy turnover and the degree of coupling to phosphorylation (intrinsic uncoupling and pathological dyscoupling). The conditions for measurement and expression of respiration vary (oxygen flux in state R, JO2R or oxygen flow in state R, IO2R). If these conditions are defined and remain consistent within a given context, then the simple symbol R for respiratory state can be used to substitute the more explicit expression for respiratory activity. R and growth of cells is supported by exogenous substrates in culture media. In media without energy substrates, R depends on endogenous substrates. R cannot be measured in permeabilized cells or isolated mitochondria. R is corrected for residual oxygen consumption (ROX), whereas R´ is the uncorrected apparent ROUTINE respiration or total cellular oxygen consumption of cells including ROX.
Respiratory acceptor control ratioRCRThe respiratory acceptor control ratio (RCR) is defined as State 3/State 4 [1]. If State 3 is measured at saturating [ADP], RCR is the inverse of the OXPHOS control ratio, L/P (when State 3 is equivalent to the OXPHOS state, P). RCR is directly but non-linearly related to the OXPHOS coupling efficiency, j≈P = 1-L/P. Whereas the normalized flux ratio j≈P has boundaries from 0.0 to 1.0, RCR ranges from 1.0 to infinity, which needs to be considered when performing statistical analyses. In intact cells, the term RCR has been used for the ratio State 3u/State 4o, i.e. for the inverse L/E ratio [2,3]. Then for conceptual and statistical reasons, RCR should be replaced by the ETS coupling efficiency, j≈E= 1-L/E [4].
Respiratory chainRCThe mitochondrial respiratory chain (RC) consists of enzyme complexes arranged to form a metabolic system of convergent pathways for oxidative phosphorylation. In a general sense, the RC includes (1) the electron transfer system (ETS), with transporters for the exchange of reduced substrates across the inner mitochondrial membrane, enzymes in the matrix space (particularly dehydrogenases of the tricarboxylic acid cycle), inner membrane-bound electron transfer complexes, and (2) the inner membrane-bound enzymes of the phosphorylation system.
Respiratory complexesCiRespiratory complexes are membrane-bound enzymes consisting of several subunits which are involved in energy transduction of the respiratory system. » MiPNet article
Respiratory stateRespiratory states of mitochondrial preparations and intact cells are defined in the current literature in many ways and with a diversity of terms. Mitochondrial respiratory states must be defined in terms of both, the coupling control state and the pathway control state.
RespirometryRespirometry is the quantitative measurement of respiration. Respiration is therefore a combustion, a very slow one to be precise (Lavoisier and Laplace 1783). Thus the basic idea of using calorimetry to explore the sources and dynamics of heat changes was present in the origins of bioenergetics (Gnaiger 1983). Respirometry provides an indirect calorimetric approach to the measurement of metabolic heat changes, by measuring oxygen uptake (and carbon dioxide production and nitrogen excretion in the form of ammonia, urea or uric acid) and converting the oxygen consumed into an enthalpy change, using the oxycaloric equivalent. Liebig (1842) showed that the substrate of oxidative respiration was protein, carbohydrates, and fat. The sum of these chemical changes of materials under the influence of living cells is known as metabolism (Lusk 1928). The amount (volume STP) of carbon dioxide expired to the amount (volume STP) of oxygen inspired simultaneously is the respiratory quotient, which is 1.0 for the combustion of carbohydrate, but less for lipid and protein. Voit (1901) summarized early respirometric studies carried out by the Munich school on patients and healthy controls, concluding that the metabolism in the body was not proportional to the combustibility of the substances outside the body, but that protein, which burns with difficulty outside, metabolizes with the greatest ease, then carbohydrates, while fats, which readily burns outside, is the most difficultly combustible in the organism. Extending these conclusions on the sources of metabolic heat changes, the corresponding dynamics or respiratory control was summarized (Lusk 1928): The absorption of oxygen does not cause metabolism, but rather the amount of the metabolism determines the amount of oxygen to be absorbed. .. metabolism regulates the respiration.
SUITSUITSUIT is the abbreviation for Substrate-Uncoupler-Inhibitor Titration. SUIT protocols are used with mt-preparations to study respiratory control in a sequence of coupling and substrates states induced by multiple titrations within a single experimental assay. Further details: Substrate-uncoupler-inhibitor titration, MitoPedia: SUIT.
SelectivitySelectivity is the ability of a sensor or method to quantify accurately and specifically the analyte or analytes in the presence of other compounds.
SensitivitySensitivity refers to the response obtained for a given amount of analyte and is often denoted by two factors: the limit of detection and the limit of quantification.
SmoothingVarious methods of smoothing can be applied to improve the signal-to-noise ratio. For instance, data points recorded over time [s] or over a range of wavelengths [nm] can be smoothed by averaging n data points per interval. Then the average of the n points per smoothing interval can be taken for each successively recorded data point across the time range or range of the spectrum to give a n-point moving average smoothing. This method decreases the noise of the signal, but clearly reduces the time or wavelength resolution. More advanced methods of smoothing are applied to retain a higher time resolution or wavelength resolution.
StabilityStability determines the accuracy of intensity and absorbance measurements as a function of time. Instability (see drift introduces systematic errors in the accuracy of fluorescence and absorbance measurements.
Substrate control stateSee Pathway control state
Substrate-uncoupler-inhibitor titrationSUITMitochondrial Substrate-uncoupler-inhibitor titration (SUIT) protocols are used with mitochondrial preparations to study respiratory control in a sequence of coupling and substrates states induced by multiple titrations within a single experimental assay.
Time resolutionTime resolution in respirometric measurements is influenced by three parameters: the response time of the POS, the data sampling interval and the number of points used for flux calculation.
Uncoupling control ratioUCRThe uncoupling control ratio, UCR, is the ratio of ETS/ROUTINE respiration (E/R) in intact cells, evaluated by careful uncoupler titrations (Steinlechner et al 1996). Compare ROUTINE control ratio (R/E) (Gnaiger 2008).
Unspecific binding of TPP+Unspecific binding of the probe molecule TPP+ in the matrix phase of mitochondria is taken into account as a correction for measurement of the mitochondrial membrane potential. External unspecific binding is the binding outside of the inner mt-membrane or on the outer side of the inner mt-membrane, in contrast to internal unspecific binding.
Warburg effectRequires definition
Zero calibrationR0Zero calibration is together with air calibration one of the two steps of the OroboPOS calibration. It is performed in the closed chamber after all the oxygen has been removed by the addition of dithionite, see MiPNet06.03 POS-calibration-SOP. Unlike air calibration it is not necessary to perform a zero calibration each day.
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