Electronic and steric factors in regioselective hydroxylation catalyzed by purified cytochrome P-450.
A reconstituted hydroxylation system consisting of electrophoretically homogeneous phenobarbital-inducible rabbit liver microsomal cytochrome P-450 (P-450 LM2), NADPH-cytochrome P-450 reductase, phospholipid, buffer, NADPH, and O2 was used to oxidize four cyclohexane derivatives: cyclohexene, methylcyclohexane, norcarane and norbornane. Cyclohexene gave only cyclohexene oxide and allylic cyclohexenol, while methylcyclohexane yielded all possible monohydric alcohols, but with 1 degrees:2 degrees:3 degrees ratios of 0.072:1:1.25. Norcarane yielded 2-norcaranol. While oxidation of norbornane produced exo-2- and endo-2-norborneols in a ratio of 3.4:1, replacement of all four exo-hydrogens by deuterium led to a reversal of the exo:endo ratio to 0.76:1. These and other observations are interpreted as evidence for a selective, hydrogen-abstracting enzyme-bound oxidant exhibiting a large intramolecular deuterium isotope effect. A transient substrate carbon radical is a probable intermediate in the hydroxylation process.
D000818:Animals; D003510:Cyclohexanes; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006900:Hydroxylation; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D011817:Rabbits; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D003510:Cyclohexanes; D003577:Cytochrome P-450 Enzyme System; D009251:NADPH-Ferrihemoprotein Reductase; D010634:Phenobarbital