Isolation of a novel hepatic CYP2-related protein from channel catfish, Ictalurus punctatus

Channel catfish (Ictalurus punctatus) have been previously shown to express two major cytochrome P450 (CYP) protein bands that are cross-reactive with anti-CYP2K1 (rainbow trout, Oncorhynchus mykiss) antibodies on Western blots. These proteins appear to be the major constitutive CYPs in channel catfish and show distinct sex- and age-specific variations in expression. Because I. punctatus is an important agricultural and ecological commodity, and because it displays a high degree of resistance to the toxic effects of many pesticides, the molecular and catalytic characteristics of its biotransformation systems are of interest to those in areas of environmental science and aquaculture research. Using a chromatographic method similar to that employed in the purification of other fish CYP2 enzymes, a single CYP2-related protein (CM-HA3) was isolated from channel catfish hepatic microsomes. The isolated protein displays a relative molecular mass of approximately 47 kDa, and a CO-reduced difference spectrum _max of 449.6 nm. The sequence of 15 residues at the amino-terminal of CM-HA3 is 27% identical to both CYP2K1 and CYP2M1 isoforms of rainbow trout. Correlational analysis was employed to characterize potential substrates for this isoform, but no significant relationship was observed with E₂ hydroxylation, testosterone hydroxylation, or 7-ethoxycoumarin O-deethylase activities. These data indicate that CM-HA3 is a CYP2 family protein, with as yet uncharacterized substrate specificities.