Hepatic and extrahepatic microsomal electron transport components and mixed-function oxygenases in the marine fish Stenotomus versicolor.

NADPH-cytochrome c reductase, benzoa]pyrene hydroxylase and aminopyrine demethylase activities in hepatic microsomes from the marine fish scup (Stenotomus versicolor) were characterized according to dependence of Ph, temperature, ionic strength and Mg²⁺. The kinetic properties of benzoa] pyrene hydroxylase were variable, depending on protein and substrate concentration, with measured K_m values for benzoa]pyrene between 4 × 10^?7 M and 4 × 10^?5 M. The K_m for aminopyrine was 7 × 10^?4 M, and NADPH-cytochrome c reductase had K_m values of 2.1 × 10^?5 M and 1.3 × 10^?5 M for cytochrome c and NADPH. respectively. NADH supported benzoa]pyrene hydroxylation at 10 per cent of the rate seen with NADPH, and no synergism was observed. Aminopyrine demethylation proceeded at least as well with NADH as with NADPH, and there was synergism when combined. NADPH- and NADH-cytochrome c reductases were detected in “microsomes” from fourteen extrahepatic tissues, including kidney, testis, foregut, gill, heart, red muscle, hindgut, buccal epidermis, pyloric caecum, spleen, brain, lens, ovary and white muscle. Benzoa]pyrene hydroxylase was detected in all but white muscle, while cytochrome P-450 and aminopyrine demethylase were detectable in fewer tissues. Reduced, CO-ligated absorption maxima in the Soret region were 450 nm for all those but liver (occasionally 449 nm) and heart (about 447 nm). The estimated turnover numbers for benzoa]pyrene hydroxylase and aminopyrine demethylase, and the influence of 7,8-benzoflavone in vitro on benzoa]pyrene hydroxylase indicate that the cytochromes P-450 in different fish tissues are not catalytically equivalent.