OXIDATION OF CAPSAICIN AND CAPSAICIN PHENOLIC PRECURSORS BY THE BASICPEROXIDASE ISOENZYME B-6 FROM HOT PEPPER

The ability of hot pepper peroxidase to oxidize the phenolic precursor s of capsaicin biosynthesis [p-coumaric acid (3), caffeic acid (4), fe rulic acid (5), vanillin (6), and vanillylamine (7)] was studied. The results showed that hot pepper peroxidase, and especially hot pepper p eroxidase isoenzyme B-6 (Prx B-6) is capable of oxidizing the phenolic precursors of capsaicin (8), caffeic acid and ferulic acid being the best substrates. Vanillylamine was the only precursor that did not act as substrate for peroxidase-catalyzed oxidations. Since the basic per oxidase isoenzyme B-6 is located in cell walls, it seems plausible tha t this isoenzyme may be involved in the insolubilization of phenylprop anoid precursors in muro. These results lend weight to the biochemical evidence for supporting the existence of an oxidative competitive sin k for phenylpropanoid intermediates of capsaicin biosynthesis, and whi ch probably competes with capsaicin itself to yield lignin-like substa nces, in the cell wall of Capsicum annuum var. Annuum.