[Influence of pH on the steady state kinetics of electron transfer through the cytochrome chain of submitochondrial particles. Kinetic model for regulating the activity of carriers by the local concentration of hydrogen ions in the membrane].

The kinetic parameters of the submitochondrial particles cytochrome chain obtained from steady-state kinetics were studied for pH dependence. The life-times of the activated states (tau) for cytochrome pairs b leads to c1 and a leads to a3 are shown to bear dissimilar dependence on pH of the medium, while for cytochrome pairs c1 leads to c and c leads to a they display practically no pH dependence at all. The rate constants of the non-activated state (alphai-kiCo) decreased for the pair b leads to c1 and increased for a leads to a3 with the increase of pH from 6.5 to 8.5. The apparent pK values obtained therefrom were 7.2 and 8.9, respectively. A kinetic model is proposed suggesting that local pH in the mitochondrial membrane, dependent on the rate of electron transfer, may be a controlling factor for the ratio of activated and non-activated carrier states. The model is in good consistence with the experimental dependences of k'i on V and the pH dependences of alpha2 for b leads to c1 and a leads to a3. It also gives a qualitative prediction for the pH dependences of the ordinate intercepts of the straight lines in l/(k'i--alphai) vs. l/V plots. The rate constants for the diffusion of hydrogen and hydroxyl ions in the membrane are estimated on the basis of our kinetic data to be 10(4)--10(5) s-1 and 10(2)--10(3) s-i, respectively.