The stereospecificity of nitrate reductase for hydrogen removal from reduced pyridine nucleotides.

The stereospecificity of the hydrogen removal from reduced pyridine nucleotides catalyzed by nitrate reductase (NADH : nitrate oxidoreductase, EC 1.6.6.1, and NAD(P)H : nitrate oxidoreductase, EC 1.6.6.2) was investigated. A high degree of enzyme purification was required to obtain conclusive results. Improvements are described for the purification of nitrate reductase from Chlorella fusca and from spinach (Spinacea oleracea, L.) leaves. The latter enzyme is shown to contain a cytochrome. With highly purified nitrate reductase preparations from Cl. fusca, Neurospora crassa, Rhodotorula glutinis and spinach leaves the stereospecificity of the reaction was determined to be predominantly of the A-type in all cases.