title: Cytochrome P-450 isozymes from the marine teleost Stenotomus chrysops: their roles in steroid hydroxylation and the influence of cytochrome b5.
abstract: Two new cytochrome P-450 forms were purified from liver microsomes of the marine fish Stenotomus chrysops (scup). Cytochrome P-450A (Mr = 52.5K) had a CO-ligated, reduced difference spectrum lambda max at 447.5 nm, and reconstituted modest benzo[a]pyrene hydroxylase activity (0.16 nmol/min/nmol P-450) and ethoxycoumarin O-deethylase activity (0.42 nmol/min/nmol P-450). Cytochrome P-450A reconstituted under optimal conditions catalyzed hydroxylation of testosterone almost exclusively at the 6 beta position (0.8 nmol/min/nmol P-450) and also catalyzed 2-hydroxylation of estradiol. Cytochrome P-450A is active toward steroid substrates and we propose that it is a major contributor to microsomal testosterone 6 beta-hydroxylase activity. Cytochrome P-450A had a requirement for conspecific (scup) NADPH-cytochrome P-450 reductase and all reconstituted activities examined were stimulated by the addition of purified scup cytochrome b5. Cytochrome P-450B (Mr = 45.9K) had a CO-ligated, reduced difference spectrum lambda max at 449.5 nm and displayed low rates of reconstituted catalytic activities. However, cytochrome P-450B oxidized testosterone at several different sites including the 15 alpha position (0.07 nmol/min/nmol P-450). Both cytochromes P-450A and P-450B were distinct from the major benzo[a]pyrene hydroxylating form, cytochrome P-450E, by the criteria of spectroscopic properties, substrate profiles, minimum molecular weights on NaDodSO4-polyacrylamide gels, peptide mapping and lack of cross-reaction with antibody raised against cytochrome P-450E. Cytochrome P-450E shares epitopes with rat cytochrome P-450c indicating it is the equivalent enzyme, but possible homology between scup cytochromes P-450A or P-450B and known P-450 isozymes in other vertebrate groups is uncertain, although functional analogs exist.
mesh_terms: D000818:Animals; D002384:Catalysis; D002848:Chromatography, DEAE-Cellulose; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003573:Cytochrome b Group / Q000502:physiology; D015786:Cytochromes b5; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005399:Fishes / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D003573:Cytochrome b Group; D007527:Isoenzymes; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases