Assay conditions and basal activity of CYP1A-dependent mixed function oxidase in parr and smolt of atlantic salmon ( Salmo salar)

Abstract

Liver microsomes were prepared from parr and smolt of Atlantic salmon ( Salmo salar), and optimal assay conditions (pH, temperature, incubation time) were established to measure basal activities, and kinetic constants (Km, Vmax) of three CYP1A-dependent mixed function oxygenases—benzo-a-pyrene hydroxylase (BAPH), 7-ethoxyresorufin-O-deethylase (EROD), and ethoxycoumarin-O-deethylase (ECOD), cytochromes P-450 and b5 content, and NADH- and NADPH-cytochrome c reductase activities. Using the determined assay conditions, we measured basal MFO activities in parr and smolt over a one-year period. Mean basal activities were as follows: EROD 0.033–0.104 nmol min −1 mg −1, BAPH 0.022–0.223 nmol min −1 mg −1, cyt-P450 0.063–0.353 nmol mg −1, NADH-cyt c reductase 45.25–71.99 nmol min −1 mg −1, NADPH-cyt c reductase 34.01–46.27 nmol min −1 mg −1, cyt-b5 0.079–0.587 nmol mg −1. There was a consistent development-related shift in basal EROD and BAPH activities in Atlantic salmon juveniles as they proceeded through smoltification.