Inhibition of membrane-bound cytochrome c oxidase by zinc ions: High-affinity Zn²⁺-binding site at the P-side of the membrane

Abstract 

In the presence of the uncoupler, external zinc ions inhibit rapidly turnover of cytochrome c oxidase reconstituted in phospholipid vesicles or bound to the membrane of intact mitochondria. The effect is promoted by electron leaks into the oxidase during preincubation with Zn²⁺. Inhibition of liposome-bound bovine cytochrome oxidase by external Zn²⁺ titrates with a K_i of 1±0.3μM. Presumably, the Zn²⁺-binding group at the positively charged side is not reactive in the oxidized enzyme, but becomes accessible to the cation in some partially reduced state(s) of the oxidase; reduction of Cu_B is tentatively proposed to be responsible for the effect.

Abbreviations: COX, cytochrome c oxidase, CCCP, carbonyl cyanide m-chlorophenyl hydrazone, EDTA, ethylenediaminetetraacetic acid, RuBpy, tris-bipyridyl complex of ruthenium(II), P- and N-sides, positively and negatively charged sides of the membrane, respectively

Keywords: Cytochrome oxidase, Zinc ions, Electron transfer inhibitors, Proton pump, Respiratory chain