Rat liver DT-diaphorase as a nitroso-reductase

Reduction of several nitroso-compounds by purified DT-diaphorase from rat liver cytosol was investigated. Among nitroso-compounds tested, 1-nitroso-2-naphthol and p-nitrosophenol were reduced in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) at rates much faster than that of nitrosobenzene. On the contrary, none of the N-nitroso-compounds tested was reduced by this enzyme. Experiments on the identification of reduction products and on the inhibition with dicoumarol and the antiserum indicated that DT-diaphorase catalyzes 4-electron reduction of C-nitroso-compounds and plays a major role in the reduction of these compounds by rat liver cytosol.