Inhibition of enzyme activities by 12-keto oleic acid.

The effect of the long chain keto acid, which is one of the secondary products from oxidative deteriolation of lipids, on the enzyme activity was investigated in vitro. Cholinesterase and succinate dehydrogenase were inhibited more effectively by 12-keto oleic acid than by linoleic acid, whereas the inhibition of trypsin by linoleic acid was greater than that caused by 12-keto oleic acid. This fact may show that the enzyme inhibition by 12-keto oleic acid is not merely due to nonspecific denaturation. The inhibitory effect of 12-keto oleic acid on acêtylcholinesterase was not protected by the presence of a-tocopherol, while the inhibition by linoleic acid was completely restored when a-tocopherol was added simultaneously. When both linoleic and 12-keto oleic acids were added at the same time, the synergistic inhibition was observed, which was partially protected by a-tocopherol. Thus the inhibition caused by 12-keto oleic acid is not only the reflection of the stimulation of lipid peroxidation induced by 12-keto oleic acid, but the specific irreversible interaction with enzyme protein.