Protonmotive activity of cytochrome c oxidase: control of oxidoreduction of the heme centers by the protonmotive force in the reconstituted beef heart enzyme

Abstract

This paper contributes to the characterization of partial steps of electron and proton transfer in mitochondrial cytochrome c oxidase with respect to their membrane arrangement and involvement in energy-linked protonmotive activity. It is shown that .DELTA..psi. electron flow from cytochrome c to heme a and from the latter and heme a3 to oxygen. The back-pressure exerted by .DELTA..psi. on electron flow from cytochrome c to heme a is consistent with the view that the latter center is buried in the membrane in a central position. The pressure exerted by .DELTA..psi. on oxidation of heme a3 by O2 indicates also that this center is buried in the membrane at some distance from the inner side and is consistent with observations showing that protons consumed in the reduction of O2 to H2O derive from the inner space. Electron flow from heme a to heme a3 is shown to be specifically controlled by .DELTA.pH and in particular by the pH of the inner phase. Analysis of the effect of DCCD treatment of oxidase vesicles reveals that concentrations of this reagent which result in selective of subunit III (Prochaska et al., 1981) produce inhibition or redox-linked proton release. Higher concentrations of DCCD which result also in modification of subunits II and IV (Prochaska et al., 1981) cause inhibition of the pH-dependent electron-transfer step from heme a to heme a3.