DICOUMAROL-SENSITIVE NADPH - PHENANTHRENEQUINONE OXIDOREDUCTASE IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS)

Phenanthrenequinone (PQ), which occurs widely as a pollutant and as a major metabolite of phenanthrene in a number of species, has been demo nstrated to undergo futile redox cycling leading to oxidative stress. In the presence of cytosolic fractions of selected channel catfish tis sues, PQ undergoes enzymatic reduction which is mediated by either NAD H or NADPH and is composed of dicoumarol-sensitive and -insensitive co mponents. Most notably, gastric cytosol catalyzed a disproportionately high level of NADPH-dependent, dicoumarol-sensitive PQ reduction as c ompared to gill, liver, and kidney cytosols. In the presence of stomac h cytosol and NADPH, PQ facilitated production of superoxide anion at rates several fold higher than those mediated by menadione. The dicoum arol-sensitive PQ-reducing agent, which we have termed NADPH: phenanth renequinone oxidoreductase (PQR), was purified by affinity chromatogra phy and was demonstrated to be separable from DT diaphorase activity i n gastric cytosol. Under aerobic conditions, purified PQR facilitates redox cycling of PQ as indicated by continued NADPH oxidation and hydr ogen peroxide production. Under anaerobic conditions, NADPH oxidation is limited to a quantity indicative of PQ reduction to the hydroquinon e. Substrate specificities, pH profiles, and kinetic characteristics c ombine to indicate that PQR represents a novel quinone reductase in th is species. (C) 1994 Academic Press, Inc.