title: A prominent feature of the conversion of P-450 to P-420 of cytochrome P-450B1 among the cytochrome P-450 isozymes.
abstract: Conversion of cytochrome P-450 to P-420 was observed with the use of three isozymes of P-450, P-450PB, P-450MC and P-450B1. The last one, which was isolated and characterized in our laboratories, is the cytochrome P-450 with high affinity for cytochrome b5. Of these isozymes, cytochrome P-450B1 is predominantly fast in the rate of conversion from P-450 to P-420 in the reduced state under carbon monoxide. p-Nitroanisole, which is the substrate of P-450B1 for demethylation, accelerated the conversion, whereas the effects of the compound on the rate of conversion of the other P-450S were small. The effect of cholate on the conversion was distinct and rapid but not very selective among the isozymes. Stabilization with glycerol for prevention of the conversion was found to be effective, for any of these isozymes. No remarkable difference was observed in the stability of the oxidized state among these isozymes when detected in the CO-reduced form. The rates of the reaction from the oxidized to the CO-reduced form were measured with these isozymes. The rate of P-450B1 was the highest in both the medium with glycerol and that without glycerol. Circular dichroism was measured with respect to conversion of P-450 to P-420. The absorption at 450 nm was related to the significant circular dichroism, while the increased absorption at 420 nm due to the conversion was not accompanied by distinct circular dichroism. These data support the concept that the heme vicinity of cytochrome P-450B1 is more labile in the structure of the reduced form under carbon monoxide than those of the other isozymes.
mesh_terms: D000818:Animals; D000840:Anisoles / Q000494:pharmacology; D002793:Cholic Acids / Q000494:pharmacology; D002942:Circular Dichroism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D005990:Glycerol / Q000494:pharmacology; D008099:Liver / Q000201:enzymology; D008297:Male; D010084:Oxidation-Reduction; D011817:Rabbits; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D000840:Anisoles; D002793:Cholic Acids; D003580:Cytochromes; C013464:cytochrome P420; D003577:Cytochrome P-450 Enzyme System; C005306:4-nitroanisole; D005990:Glycerol