title: The mechanism of action of cytochrome P-450. Occurrence of the 'NIH shift' during hydroperoxide-dependent aromatic hydroxylations.
abstract: The mechanism of liver microsomal aromatic hydroxylation has been investigated by using cumene hydroperoxide as the hydroxylating agent and comparing this reaction with the NADPH-dependent reaction. The conversion of [4-(3)H]acetanilide to 4-hydroxyacetanilide by rat liver microsomes (or purified cytochrome P-450) in the presence of either cumene hydroperoxide or NADPH is attended by comparable 'NIH shifts'. This indicates that hydroxylation in the two systems proceeds via a common intermediate, presumably an arene oxide. The intermediacy of an arene oxide, phenanthrene-9,10-oxide, is established by incubating [3-(3)H]-phenanthrene with rat-liver microsomes and cumene hydroperoxide in the presence of either non-radioactive phenanthrene-9,10-oxide as a 'trap' or in the presence of cyclohexene oxide, an inhibitor of the enzyme epoxide hydrase. Incubation of phenanthrene with cumene hydroperoxide in an 18O-enriched medium has confirmed that the oxygen atom in phenanthrene-9,10-oxide is derived from the hydroperoxide and not from the medium.
mesh_terms: D000083:Acetanilides; D000818:Animals; D001555:Benzene Derivatives; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism; D006900:Hydroxylation; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010545:Peroxides; D010634:Phenobarbital / Q000494:pharmacology; D011817:Rabbits; D051381:Rats
chemical_list: D000083:Acetanilides; D001555:Benzene Derivatives; D003580:Cytochromes; D010545:Peroxides; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; C007164:cumene hydroperoxide; D010634:Phenobarbital