THE EFFECT OF THE PROTONMOTIVE FORCE ON THE REDOX STATE OF MITOCHONDRIAL CYTOCHROMES

In the absence of kinetic limitations, as determined either by high substrate concentrations or by absence of respiratory chain inhibitors, we have observed that: (a) the relationship between the percentage reduction of the cytochromes and the protonmotive force is linear in the case of cytochrome c and biphasic in the case of cytochrome b, (b) the redox state of cytochrome c depends only on the membrane potential and not on the total proton motive force and (c) the alkalinization of the matrix enhances the extent of cytochrome c reduction because of the marked inhibitory effect on the cytochrome oxidase activity. Thus, although the redox states of the b, c and aa(3) mitochondrial cytochromes depend on the protonmotive force, the quantitative correlation between the two parameters and the relative effects of the electrical and chemical components of the force differ among the various cytochromes.