[Purification and properties of NAD-reductase from phototrophic bacterium Thiocapsa roseopersicina]

The purification by affinity chromatography up to homogeneity and the properties of NAD-reductase from purple sulfur bacterium Thiocapsa roseopersicina, strain BBS, are described. The molecular weight of NAD-reductase is about 80000; pI is 3.9. The enzyme consists of two subunits. According to the stabilizing effect of FAD at preparative electrophoresis and the inhibitory effect of atebrine NAD-reductase is a flavoprotein. The bulk of the enzyme (about 75%) is localized in the cell periplasmic space. NAD-reductase is less thermostable and has a lower O2 stability as compared to the NADP-reductase from the same organism. The enzyme is specific to NADH ane catalyzes the menadione-reductase reaction, diaphorase reaction of benzyl viologen and methyl viologen reductions. In the presence of NADH NAD-reductase reduces cytochromes c552 and "c3" from T. roseopersicina and forms a complex with spinach ferredoxin.