Interaction of the bacterial terminal oxidase cytochrome bd with nitric oxide

Cytochrome bd is a prokaryotic terminal oxidase catalyzing O-2 reduction to H2O. The oxygen-reducing site has been proposed to contain two hemes, d and b(595), the latter presumably replacing functionally Cu-B of heme-copper oxidases. We show that NO, in competition with O-2, rapidly and potently (K-i = 100 +/- 34 nM at similar to70 muM O-2) inhibits cytochrome bd isolated from. Escherichia coli and Azotobacter vinelandii in turnover, inhibition being quickly and fully reverted upon NO depletion. Under anaerobic reducing conditions, neither of the two enzymes reveals NO reductase activity, which is proposed in heme-copper oxidases to be associated with Cu-B. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.