Metabolic activation and covalent binding of benzo[a]pyrene to deoxyribonucleic acid catalyzed by liver enzymes of marine fish

Abstract

Metabolic activation and covalent binding of benzo[a]pyrene (BP) to deproteinized salmon sperm DNA by supernatant fractions (10,000 g) of liver homogenates isolated from untreated, 3-methylcholanthrene (3-MC) or BP-treated starry flounder (Platichthys stellatus) and coho salmon (Oncorhynchus kisutch) were investigated. The influence of temperature, pH, time and concentrations of protein, BP, NADPH and DNA on covalent binding was investigated to obtain optimum conditions for in vitro binding (pmoles of BP equivalents bound/mg DNA/mg protein) of [(3)H]BP to DNA for each of the two fish species. When the supernatant fractions from untreated starry flounder were used, the covalent binding of BP to DNA was 7.5 and 2.5 times greater than the values obtained with the supernatant fractions from untreated coho salmon or rat respectively. Treatment of both fish species with 3-MC or BP resulted in a marked (10- to 53-fold) increase in the binding. Ethyl acetate-extractable metabolites formed by fish liver supernatant fractions consisted of BP dihydrodiols (4,5-, 7,8-, and 9,10-dihydrodiols), phenols (3-OH, 9-OH, and 7-OH), quinones (3,6-, 1,6- and 6,12-Q) and BP 4,5-oxide. For both fish species, BP 9,10-dihydrodiol and BP 7,8-dihydrodiol were the major metabolites comprising as much as 48-72 per cent of the total ethyl acetate-extractable metabolites; 3-hydroxy BP was also present in significant amounts. The ratio of the non-K region dihydrodiols to phenols was significantly greater for both fish species compared to rat.