Nitric oxide ejects electrons from the binuclear centre of cytochrome c oxidase by reacting with oxidised copper: a general mechanism for the interaction of copper proteins with nitric oxide?

Small increases in NO concentration can inhibit mitochondrial oxygen consumption by reacting at the binuclear haem a(3)/Cu-B oxygen reduction site of cytochrome c oxidase, Here we demonstrate that under normal turnover conditions NO reacts initially with the oxidised CUB rather than the haem a(3). We propose that hydration of an initial Cu+/NO+ complex forms nitrite, a proton and CUB+; the latter ejects an electron from the binuclear centre and results in the observed (100 s(-1)) reduction 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 Societies.