CYTOCHROME-C-OXIDASE CATALYSIS OF THE REDUCTION OF NITRIC-OXIDE TO NITROUS-OXIDE

Reduction of nitric oxide (NO) to nitrous oxide (N2O) is catalyzed by bovine heart cytochrome c oxidase (CcO) in anaerobic solutions at pH 7.2 and 20 degrees C. Cyanide inhibits and forms Fea33+CN. The mononitrosyl (Fea32+NO), but not the dinitrosyl (Fea32+NO; Cu-B(+) NO), is a likely intermediate in N2O formation. one-electron reduction of NO at Fe-a3(2+) could yield N2O via HNO. However, a two-electron reduction of the NO ligand to give an intermediate that reacts with a second NO to give N2O and H2O appears more likely. Conversion of NO to N2O is favored by low levels of both NO and O-2; higher NO levels can inhibit both cytochrome c oxidase and NO reductase activities. Raising the O-2, level will favor catalysis of NO oxidation to NO2 by CcO. The reactions of NO and the specific CcO activity that occur in tissue will be critically dependent on NO, O-2, and CcO levels. (C) 1995 Academic Press, Inc.