title: Radical rebound mechanism in cytochrome P-450-catalyzed hydroxylation of the multifaceted radical clocks alpha- and beta-thujone.
abstract: Alpha-thujone (1alpha) and beta-thujone (1beta) were used to investigate the mechanism of hydrocarbon hydroxylation by cytochromes P-450(cam) (CYP101) and P-450(BM3) (CYP102). The thujones are hydroxylated by these enzymes at various positions, but oxidation at C-4 gives rise to both rearranged and unrearranged hydroxylation products. Rearranged products result from the formation of a radical intermediate that can undergo either inversion of stereochemistry or ring opening of the adjacent cyclopropane ring. Both of these rearrangements, as well as a C-4 desaturation reaction, are observed. The ring opening clock gives oxygen rebound rates that range from 0.2 x 10(10) to 2.8 x 10(10) s(-1) for the different substrate and enzyme combinations. The C-4 inversion reaction provides independent confirmation of a radical intermediate. The phenol product expected if a C-4 cationic rather than radical intermediate is formed is not detected. The results are consistent with a two-state process and provide support for a radical rebound but not a hydroperoxide insertion mechanism for cytochrome P-450 hydroxylation.
authors.affiliation: Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143-2280, USA.
authors.forename: Xiang
authors.initials: X
authors.lastname: He
authors.forename: Paul R Ortiz
authors.initials: PR
authors.lastname: de Montellano
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D000081008:Bicyclic Monoterpenes; D019475:Camphor 5-Monooxygenase / Q000378:metabolism*; D002384:Catalysis; D000081007:Cymenes; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006900:Hydroxylation; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D039821:Monoterpenes / Q000737:chemistry* / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase; D010084:Oxidation-Reduction; D011485:Protein Binding
chemical_list: D001426:Bacterial Proteins; D000081008:Bicyclic Monoterpenes; D000081007:Cymenes; D005609:Free Radicals; D039821:Monoterpenes; C005790:beta-thujone; D003577:Cytochrome P-450 Enzyme System; C073316:carvacrol; D006899:Mixed Function Oxygenases; D019475:Camphor 5-Monooxygenase; D009251:NADPH-Ferrihemoprotein Reductase; C052423:flavocytochrome P450 BM3 monoxygenases