Talk:Protonmotive force
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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 a mt-matrix pH 8, the proton activity is 10-8 corresponding to a concentration of free protons of 0.01 Β΅molβL-1 (6β1015 H+βL-1). For a mt-matrix volume of 0.3 Β΅m3βmtΒ-1 (Schwertzmann et al 1986; 3β10-16 Lβmt-1) the molar amount of protons is 3β10-24 molβmtΒ-1. Multiplied by the Avogadro constant (6β1023 xβmol-1), the number of protons per mitochondrion is βΌ2 H+βmt-1. A similar result of 6 H+βmt-1 is obtained with reference to a mt-matrix volume per mt-protein of 1 Β΅Lβmg-1 and 109 mtβmg-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 Lβmg-1 protein, the volume fraction is Vmt/V=0.0001 or 0.1 Β΅LβmL-1. At pH 8, 0.1 Β΅L mitochondrial matrix contain 10-15 mol H+ equivalent to 6β108 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.