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Talk:Protonmotive force

From Bioblast

Picked up


In prep: The Blue Book 2019

Gnaiger E 2019-09-05 

Section 8.3.6. Moles and numbers

Why should we consider the particle (molecular) format of quantum and statistical mechanics in mitochondrial physiology? At pH 8 in the mt-matrix the proton activity is 10-8 corresponding to a concentration of free protons of 0.01 µmol∙L-1 (6∙1015 H+∙L-1). For a mt-matrix volume of 0.3 µm3∙mt­-1 (Schwerzmann et al 1986; 3∙10-16 L∙mt-1) the molar amount of protons is 3∙10-24 mol∙mt­-1. Multiplied by the Avogadro constant (6∙1023 x∙mol-1), the number of protons per mitochondrion is ∼2 H+∙mt-1. A similar result of 6 H+∙mt-1 is obtained with reference to a mt-matrix volume per mt-protein of 1 µL∙mg-1 and 109 mt∙mg-1 protein. Thus we can expect only a few protons in a single mitochondrion on average at any point of time. This should be given more thought in the discussion of fluctuations and mitochondrial heterogeneity, particularly in single cell analysis with typically 300 mitochondria per cell. Animated cartoons on the electron transfer system with too many bouncing protons propagate a false image.
When adding a mt-concentration of 0.1 mg protein per mL to a respirometric chamber with a mt-matrix volume, Vmt, of 10-6 L∙mg-1 protein, the volume fraction is Vmt/V=0.0001 or 0.1 µL∙mL-1. At pH 8, 0.1 µL mitochondrial matrix contain 10-15 mol H+ equivalent to 6∙108 protons. Thus statistically relevant information can be obtained on the protonmotive force when using large numbers of mitochondria even at high dilution in a respirometric chamber of 2 mL, containing >1 billion H+ in the mt-matrix. Because quantities are quantized, thermodynamic terms such as temperature, Gibbs energy, pH and the pmF can be defined only on the basis of large numbers.
References
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