NITRIC-OXIDE EJECTS ELECTRONS FROM THE BINUCLEAR CENTER OF CYTOCHROME-C-OXIDASE BY REACTING WITH OXIDIZED COPPER - A GENERAL MECHANISM FOR THE INTERACTION OF COPPER PROTEINS WITH NITRIC-OXIDE

Small increases in NO concentration can inhibit mitochondrial oxygen c onsumption by reacting at the binuclear haem a(3)/Cu-B oxygen reductio n site of cytochrome c oxidase, Here we demonstrate that under normal turnover conditions NO reacts initially with the oxidised CUB rather t han the haem a(3). We propose that hydration of an initial Cu+/NO+ com plex forms nitrite, a proton and CUB+; the latter ejects an electron f rom the binuclear centre and results in the observed (100 s(-1)) reduc tion of other electron transfer centres in the enzyme (haem a and CUA) These reactions may have implications for the interactions of NO with other copper proteins. (C) 1997 Federation of European Biochemical So cieties.