Effect of cytochrome c on the linoleic acid–degrading activity of porcine leukocyte 12-lipoxygenase

Hemoproteins are known to have quasilipoxygenase activity that converts linoleic acid (LA) to its hydroperoxides. However, it is not still clear whether, like lipoxygenases, hemoproteins can produce LA hydroperoxides when the LA is part of a mixture containing many different saturated and unsaturated fatty acids. In this study, we found that such hemoprotein as cytochrome c (Cyt c) did not produce LA hydroperoxides from the phospholipase A2 (PL-A2) hydrolysis products of egg yolk phosphatidylcholine (PC). We also found that traces of hydroperoxides and a high concentration of the target unsaturated fatty acid (LA) needs to be present in a fatty acid mixture before the quasi-lipoxygenase activity of Cyt c becomes apparent. We also attempted to elucidate how Cyt c interact with porcine leukocyte 12-lipoxygenase (12-LOX). Hemoproteins are known to possess pseudo-lipohydroperoxidase activity, and can remove the hydroperoxides of unsaturated fatty acids from a reaction mixture. However, we found that Cyt c catalyzed the reaction by which hydroperoxides degrade LA, and thus enhanced the LA-degrading activity of 12-LOX. This hemoprotein-induced promotion of the ability of 12-LOX to degrade LA was observed even when the reaction mixture contained many different saturated and unsaturated fatty acids.