Inhibition of proton pumping in membrane reconstituted bovine heart cytochrome c oxidase by zinc binding at the inner matrix side

AbstractA study is presented on the effect of zinc binding at the matrix side, on the proton pump of purified liposome reconstituted bovine heart cytochrome c oxidase (COV). Internally trapped Zn2+ resulted in 50% decoupling of the proton pump at level flow. Analysis of the pH dependence of inhibition by internal Zn2+ of proton release in the oxidative and reductive phases of the catalytic cycle of cytochrome c oxidase indicates that Zn2+ suppresses two of the four proton pumping steps in the cycle, those taking place when the 2 OH− produced in the reduction of O2 at the binuclear center are protonated to 2 H2O. This decoupling effect could be associated with Zn2+ induced conformational alteration of an acid/base cluster linked to heme a3