Nitroreductase activity of heart lipoamide dehydrogenase.

A novel reaction catalysed by lipoamide dehydrogenase is described. In the presence of NADH, lipoamide dehydrogenase reduces the nitro group of 4-nitropyridine and 4-nitropyridine N-oxide. The elution profiles from a DEAE-cellulose column for the dehydrogenase and nitroreductase activities are identical. Chemical modifications of critical amino acid residues suggest that the two activities share a common catalytic domain. Nitro reduction catalysed by lipoamide dehydrogenase was monitored spectrophotometrically and chromatographically. The major product from the enzymic reduction of 4-nitropyridine was isolated and characterized structurally as NN-bis(pyridinyl)hydroxylamine, which is formed presumably via 4-hydroxyaminopyridine in a four-electron redox reaction.