酸化脂質

Hydrolysis of lecithin with phospholipase A (EC. 3. 1. 1. 4) was markedly inhibited when the lecithin had been oxidized, and preliminary trials showed that the autoxidized lecithin was not only hydrolyzed with the enzyme as a substrate but inactivated the enzyme directly. Therefore the inhibition of phospholipase A by autoxidized lipid was studied was observed in linolenate which was oxidized at 40℃ for four days. By method-A in which the phospholipase A activity was determined after preincubation of the enzyme with the autoxidized linolenate at 25℃ for 30min, 0.8μg of phospholipase A was brought to 30% loss of the activity by 1.2μg of the autoxidized linolenate, while by method-B in which the activity was determined in the presence of the autoxidized linolenate without the preincubation, the same loss rate of the enzyme activity (0.8μg) required 800 μg of the autoxidized linolenate. In order to identify the active compopunds to inhibit the enzyme, the autoxidized linolenate was fractionated by gel chromatography on Bio-Beads S-X3 column. The inhibitory action of each fraction on the enzyme was determined by method-A and -B, and the following results were obtained: by method-A, polymer > dimer > degradation product; by method-B, degradation product > polymer dimer. Then the decomposition product fraction was analyzed by GLC after conversions of carbonyl into dimethylhydrazone, of hydroxy group into trimethylsilyl ether and of carboxyl group into methoyl ester, and the compounds that decreased after reaction with the enzyme were identified by GC-MS. The active compounds to inhibit phospholipase A were 9-formyl-8-nonenoate, 10-formyl-9-decenoate, 11-formyl-9-hydroxy-10-undecenoate, 9-hydroxy-10-undecenoate and 11-hydroxy-9-undecenoate. These were conjugated carbonyl or conjugated hydroxy compound.