The reactions of copper proteins with nitric oxide

Nitric oxide (NO) can act as a ligand for copper atoms and may also engage in redox chemistry with the metal once bound, Furthermore NO posses an unpa ired electron which can couple with the unpaired electron on Cu2+. These pr operties have been exploited to probe the active sites of copper-containing enzymes and proteins, We review these studies. In addition to the use as a spectroscopic probe for the active site we draw attention to the rapid rea ctions of NO at the copper sites in Cytochrome c oxidase (CcO) and laccase. These reactions in CcO occur in the ms time range, at low NO concentration s and in the presence of oxygen and may therefore be of physiological relev ance to the control of respiration. Finally we speculate on the wider role that NO may play in regulation of an important group of Type 2 copper conta ining enzymes. (C) 1999 Elsevier Science B.V. All rights reserved.