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 a3/CuB 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 a3. 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.