The effect of energization on the apparent Michaelis–Menten constant for oxyge in nmitochondrial respiration

Lineweaver–Burk plots of 1/v against 1/[O2] for rat liver mitochondrial respiration with succinate or ascorbate+NNN′N′-tetramethyl-p-phenylenediamine as substrates are non-linear. In state 3u (uncoupled by trifluoromethoxycarbonyl cyanide phenylhydrazone) such plots tend to be concave upward, whereas in state 4 (energized) the plots were concave downward. The apparent Km for oxygen is larger in state 4 than in state 3u, despite the higher turnover in the latter system. It is postulated that at least one reversible reaction occurs between cytochrome c and cytochrome c oxidase, whose rate is increased on energization (reversed electron transfer); a model including such a reaction is proposed which accounts semiquantitatively for the observations.