Isolation and characterization of a novel cytochrome P450 (CYP2 family) isoform from channel catfish

Channel catfish (Ictalurus punctatus) express at least four isoforms of cytochrome P450 (CYP) that are cross-reactive with anti-CYP2K1 (rainbow trout) antibodies. These proteins appear to be the major constitutive CYPs in the liver of I. punctatus and show distinct sex- and age-specific variations in expression. The objective of the present work was to purify a CYP2-related hepatic CYP from I. punctatus. Hepatic microsomes were prepared from channel catfish liver and solubilized with sodium cholate and polidocanol. CYP proteins were precipitated with polyethyleneglycol and applied to an octylamino-Sepharose CL-4b column. CYP-containing fractions were subsequently subjected to chromatography on DEAE-sepharose, HA-ultragel, and CM-cellulose columns. A single heme protein (ca. 47 kDa), which reacted with anti-CYP2K1 antibodies, was resolved. A sequence for the first 15 amino acids was determined. This sequence showed homology with both CYP2M1 and CP2K1 isoforms. Expression of this band is down regulated by exposure to ethanol and fenitrothion. However, no correlation with several CYP-mediated catalytic activities has been detected as yet.