Oxidation of omega-oxo fatty acids by cytochrome P450(BM-3) (CYP102)

Cytochrome P450 enzymes oxidize aldehydes either to the corresponding acid or, via a decarboxylation mechanism, to an olefin one carbon shorter than the parent substrate, To explore the factors that control partitioning between these two pathways, we have examined the cytochrome P450(BM-3) (CYP102)-catalyzed oxidation of fatty acids with a terminal aldehyde group. P450(BM-3) oxidizes 18-oxooctadecanoic, 16-oxohexadecanoic, 14-oxotetradecanoic, and 12-oxododecanoic acids exclusively to the corresponding alpha,omega-diacids, The rates of these oxidations decrease in the order C-16 > C-18 similar or equal to C-14 > C-12. NO kinetic isotope effect is observed nor is the catalytic outcome altered when the aldehyde hydrogen is replaced by a deuterium in 16-oxohexadecanoic acid, The only product observed with 16-oxohexadecanoic acid is the diacid even when a 13,14-double bond or 15-methyl groups, substitutions that should stabilize the proposed radical intermediate generated by decarboxylation, are present. The oxidation of 16-oxohexadecanoic acid is not supported by H2O2. The results demonstrate that aldehyde oxidation by cytochrome P450(BM-3) is insensitive to changes in substrate structure expected to stabilize the transition state for decarboxylation. Decarboxylation, in contrast to the oxidation of aldehydes to acids, depends on specific substrate-protein interactions and is enzyme-specific. (C) 1996 Academic Press, Inc.