DT DIAPHORASE [NAD(P)H-(QUINONE ACCEPTOR) OXIDOREDUCTASE] IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS) - KINETICS AND DISTRIBUTION

The flavin-containing enzyme, DT diaphorase [NAD(P)H: (quinone acceptor) oxidoreductase, DTD] has been studied extensively in mammalian species as a quinone detoxifying agent. However, DTD in aquatic species has received relatively little attention. DTD activity (dicoumarol-sensitive dichlorophenolindophenol reduction) was characterized in four organs of the channel catfish, Ictalurus punctatus. Optimal conditions of substrate and cofactor concentration for hepatic cytosolic activity were determined. Alkaline pH activity data indicated that DTD activity in the organs tested was maximal in the pH range 7-9 and declined at higher values. Detectable DTD activities were observed in liver mitochondrial, microsomal and cytosolic fractions. A distinct gradient in cytosolic DTD levels among four organs was observed as follows: stomach > gill > liver > posterior kidney. This gradient was demonstrated in tissues of juvenile as well as adult male and female fish, with no qualitative differences in the gradient among the three groups. Inhibition of DTD by the anticoagulant dicoumarol was observed to be competitive with respect to NADH. Kinetic data revealed no apparent gradient in either K(m) or K(i) values corresponding to the observed organ-specific activity gradient. The implications of the observed interorgan differences in DTD activity and the role of this enzyme in quinone metabolism are discussed.