Olefin oxidation by cytochrome P-450: evidence for group migration in catalytic intermediates formed with vinylidene chloride and trans-1-phenyl-1-butene.

Oxidation of the carcinogen vinylidene chloride (VDC) by rat liver cytochrome P-450 (P-450) in microsomal and purified enzyme systems produced both ClCH2CO2H and Cl2CHCHO with concomitant suicide inactivation of three of the eight P-450 isozymes examined. The proposed intermediary role of VDC oxide in ClCH2CO2H and Cl2CHCHO production was evaluated by using chemical and kinetic studies. Aqueous decomposition of authentic VDC oxide, prepared by m-chloroperoxybenzoic acid oxidation of VDC and characterized by nuclear magnetic resonance (NMR) and mass spectrometry, failed to produce Cl2CHCHO and yielded ClCH2CO2H only at pH less than 2. Moreover, kinetic studies of VDC oxide production in the iodosobenzene-supported oxidation of VDC by P-450 did not support its proposed role as an obligate intermediate in the formation of ClCH2CO2H and Cl2CHCHO. [2,2-2H2]VDC was synthesized and found to be oxidized to Cl2C2HCO2H by microsomes supplemented with aldehyde dehydrogenase and NAD+, indicating transfer of deuterium in the formation of the precursor Cl2C2HC2HO. To test the hypothesis that the heme Fe(III) of P-450 acts as a Lewis acid in catalyzing the rearrangement of a transient epoxide intermediate to Cl2CHCHO, the decomposition of VDC oxide in the presence of Fe(III) was studied. While FeBr3-saturated CHCl3 effected approximately 50% rearrangement of epoxide to Cl2CHCHO, neither an equivalent concentration of (meso-tetraphenylporphyrinato)iron(III) chloride in CHCl3 nor highly purified cytochrome P-450 in aqueous buffer produced Cl2CHCHO from VDC oxide. Parallel studies using trans-1-phenylbutene 1,2-oxide, a stable model epoxide, indicated that, although binding of epoxide to P-450 did occur, ferric P-450 did not catalyze epoxide degradation.(ABSTRACT TRUNCATED AT 250 WORDS)