EXPOXIDATION OF C-18 UNSATURATED FATTY-ACIDS BY CYTOCHROMES P4502C2 AND AND P4502CAA

The regioselective epoxidation of oleic, linoleic, alpha-linolenic, an d gamma-linolenic acid by cytochromes P4502CAA and P4502C2 was charact erized. Epoxide metabolites for all fatty acids were resolved by norma l phase HPLC and identified by gas chromatography and mass spectrometr y, Both isoforms epoxidized the single double bond in oleic acid and b oth double bonds in linoleic acid. The ratio of the two epoxides produ ced with linoleic acid (1.6:1 for the 12,13- and 9,10-epoxides) was si milar for both enzymes. When a-linolenic acid was the substrate, all t hree epoxides were produced in about equal ratios with both enzymes. I n contrast for the omega-6 fatty acid, gamma-linolenic acid, both enzy mes produced only the 9,10- and 12,13-epoxides. Furthermore, the ratio of the metabolites produced by each enzyme was significantly differen t. The ratios of 12,13-epoxide to 9,10-epoxide for gamma-linolenic wer e 11.0 +/- 0.19 and 5.8 +/- 1.2 for P4502CAA and P4502C2, respectively . These results suggest that there may be subtle differences in the st ructure of 2C2 and 2CAA and also indicate that P450 may be important i n the generation of potentially active epoxide metabolites of unsatura ted fatty acids other than arachidonic acid.