Oxidation of omega-oxo fatty acids by cytochrome P450BM-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 P450BM-3 (CYP102)-catalyzed oxidation of fatty acids with a terminal aldehyde group. P450BM-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 C16 > C18 approximately = C14 > C12. 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 P450BM-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.
Davis
S C
SC
Department of Pharmaceutical Chemistry, School of Pharmacy, and Liver Center, University of California, San Francisco 94143-0446, USA.
Sui
Z
Z
Peterson
J A
JA
Ortiz de Montellano
P R
PR
D000447:Aldehydes / Q000378:metabolism*; D000475:Alkenes / Q000378:metabolism; D001426:Bacterial Proteins; D002264:Carboxylic Acids / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003903:Deuterium; D005227:Fatty Acids / Q000737:chemistry*; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D008956:Models, Chemical; D009251:NADPH-Ferrihemoprotein Reductase; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D013379:Substrate Specificity
D000447:Aldehydes; D000475:Alkenes; D001426:Bacterial Proteins; D002264:Carboxylic Acids; D005227:Fatty Acids; D003577:Cytochrome P-450 Enzyme System; D003903:Deuterium; D006899:Mixed Function Oxygenases; D009251:NADPH-Ferrihemoprotein Reductase; C052423:flavocytochrome P450 BM3 monoxygenases