Diaphorases functions

Boison, G., Schmitz, O., Schmitz, B. and Bothe, H. (1998) Unusual gene arrangement of the bidirectional hydrogenase and functional analysis of its diaphorase subunit HoxU in respiration of the unicellular cyanobacterium Anacystis nidulans. Curr. Microbiol., 36, 253-8. 

L. Emster, DT-diaphorase its structure, function, regulation, and role in antioxidant defence and cancer chemotherapy. In K. Yagi (ed.). Pathophysiology of Lipid Peroxides and Related Free Radicals Japan Sci. Soc. Press, Tokyo/S.Karger, Basel, 1998, pp. 149-168. 

Schmidt, H.H., Gagne, G.D., Nakane, M. etal. (1992). Mapping of neural nitric oxide synthase in the rat suggests frequent co-localization with NADPH diaphorase but not with soluble guanylyl cyclase, and novel paraneural functions for nitrinergic signal transduction. J. Histochem. Cytochem. 40, 1439-1456. 

Lipoxygenase Malate dehydrogenase Metallo-endopeptidase N-Methyl transferase Monoamine oxidase Mixed-function oxidase (cytochrome P450 dependent) NADH2 diaphorase NADPH2 diaphorase Neutral endopeptidase 24.11 Nitro oxide synthase Nitro reductase 5 -Nucleotidase Peroxidase... 

An NADH diaphorase has been purified from human erythrocytes. The enzyme activity can be determined in a system containing 2.6 dichlorophenol-indo-phenol, Tris HCl buffer (pH 7.55), EDTA, and the enzyme. The reduction of 2.6 dichlorophenol-indo-phenol is followed spectrophotometrically. The purified enzyme contains one mole of a flavin adenine nucleotide (probably FAD) per 195,000 g of protein. The enzyme functions with either NADPH or NADH as hydrogen donor, but the affinity for NADH is almost 10 times greater than that for NADPH. 

In this scheme no function has been assigned to cytochrome a, which may be a component of cytochrome oxidase. The role of diaphorase and of cytochrome b still requires clarification. Further evidence for the existence of the enzyme referred to as Slater s factor is required. 

The enzymatic reduction of the nitro group involves the stepwise addition of six reducing equivalents potentially derived from reduced pyridine nucleotides (Fig. 8). The first reaction yields a nitroso derivative which is subsequently reduced to a hydroxylamine the hydroxylamino compound is then reduced to the amine. In most systems studied to date (Cemiglia and Somerville, this volume) a single nitroreductase enzyme is responsible for all three reactions and there is little or no accumulation of the intermediates. However, reduction of nitro compounds does not seem to be the physiological function of the enzymes that have been reported to carry out these reactions. Diaphorases (23), ferredoxin-NADPH reductase (33), and a variety of other enzymes from procaryotes and eucaryotes have been shown to catalyze the fortuitous reduction of aromatic nitro groups. 

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