Coupled oxidation of carotene by lipoxygenase requires two isoenzymes.

Abstract The coupled bleaching of carotene observed during the lipoxygenase-catalyzed hydroperoxidation of polyunsaturated fats had previously been shown in our laboratory to be very poorly catalyzed by pure lipoxygenase-1 of soybean. It has now been shown that the other two major isoenzymes in soybean, lipoxygenase-2 and -3, are also individually poor catalysts for the bleaching. However, a combination of lipoxygenase-1 plus lipoxygenase-3, or lipoxygenase-2 plus lipoxygenase-3 are effective in promoting the concomitant oxidation of carotene. Preformed 13-hydroperoxy-9- cis -11- trans octadecadienoate obtained by the action of lipoxygenase-1 on linoleic acid or its ester can replace lipoxygenase-1, when lipoxygenase-3 is present. However, the 9-hydroperoxy-10- trans -12- cis -isomer produced enzymatically with potato lipoxygenase is relatively ineffective.