An exploration of how the thermodynamic efficiency of bioenergetic membrane systems varies with c-subunit stoichiometry of F1F0 ATP synthases

Recently the F-0 portion of the bovinemitochondrial F1F0-ATP synthase was shown to contain eight 'c' subunits (n = 8). This surprised many in the field, as previously, the only other mitochondrial F-0 (for yeast) was shown to have ten 'c' subunits. The metabolic implications of 'c' subunit copy number explored in this paper lead to several surprising conclusions: (1) Aerobically respiring E. coli (n = 10) and animal mitochondria (n = 8) both have very high F1F0 thermodynamic efficiencies of approximate to 90 % under typical conditions, whereas efficiency is only approximate to 65 % for chloroplasts (n = 14). Reasons for this difference, including the importance of transmembrane potential (Delta Psi) as a rotational catalyst, as opposed to an energy source, are discussed. (2) Maximum theoretical P/O ratios in animal mitochondria (n = 8) are calculated to be 2.73 ATP/NADH and 1.64 ATP/FADH(2), yielding 34.5 ATP/glucose (assuming NADH import via the malate/aspartate shuttle). The experimentally measured values of 2.44 (+/- 0.15), 1.47 (+/- 0.13), and 31.3 (+/- 1.5), respectively, are only about 10 % lower, suggesting very little energy depletion via transmembrane proton leakage. (3) Finally, the thermodynamic efficiency of oxidative phosphorylation is not lower than that of substrate level phosphorylation, as previously believed. The overall thermodynamic efficiencies of oxidative phosphorylation, glycolysis, and the citric acid cycle are approximate to 80 % in all three processes.