Mitochondrial Thermodynamic Efficiency and P/O Ratios are Controlled by the F1F0 ATP Synthase C-Subunit Stoichiometry

Abstract

Recently the F0 portion of the bovine mitochondrial F1F0-ATP synthase was shown to contain eight ‘c’ subunits (n = 8). This surprised many in the field, as previously, the only other mitochondrial F0 solved (for yeast) had n = 10 ‘c’ subunits. The metabolic implications of ‘c’ subunit copy number are explored in this paper: Typical aerobically respiring E. coli (n = 10) and mitochondria (n = 8) are both found to have very high F1F0 thermodynamic efficiencies of ≈ 90%, whereas efficiency is lower at ≈ 65% for chloroplasts (n = 14). Reasons for this difference are discussed. Maximum mitochondrial P/O ratios in animal mitochondria (n = 8) are calculated to be 2.73 ATP/NADH and 1.64 ATP/FADH2, yielding 34.5 ATP/glucose. The experimentally measured values of 2.52, 1.53, and 32.3, respectively, are only about 7% lower. 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 citric acid cycle are ≈ 80% in all three processes.