Cytochrome P450 Expression in Rainbow Trout: An Overview

Abstract

The cytochromes P450 are the major enzymes involved in the oxidative metabolism of both endogenous and exogenous chemicals in fish (Buhler and Williams, 1989; Goksoyr and Forlin, 1992; Guengerich, 1992) and other animals (Guengerich, 1990). The membrane-bound cytochromes P450, predominately localized in the liver but also found in lower concentrations in other tissues, comprise a superfamily of closely related heme-containing enzymes of similar structure and diverse functions (Nelson et al., 1993). Initially, it was thought that fish lacked cytochrome P450-linked monooxygenases (Brodie and Maickel, 1962) but studies carried out in the late 1960’s (Buhler, 1966; Buhler and Rasmusson, 1968; Dewaide and Henderson, 1968) showed livers of rainbow trout and other fishes contained these enzymes. Enzyme activities were generally lower than in mammals and the fish P450s had temperature optima of about 25°C, explaining why they were not detected in the earlier studies where incubations at a higher temperature were employed. Subsequently, as observed in mammals, multiple cytochrome P450 forms were discovered in fishes (Klotz et al., 1983; Miranda et al., 1989; Williams and Buhler, 1982, 1983a, 1984) and several laboratories have succeeded in purifying and characterizing cytochrome P450 enzymes from numerous marine and freshwater fishes (for reviews see Andersson and Förlin, 1992; Buhler and Williams, 1989; Goksoyr and Förlin, 1992; Stegeman, 1989).