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

The ability of hot pepper peroxidase to oxidize the phenolic precursors of capsaicin biosynthesis [p-coumaric acid (3), caffeic acid (4), ferulic acid (5), vanillin (6), and vanillylamine (7)] was studied. The results showed that hot pepper peroxidase, and especially hot pepper peroxidase 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 peroxidase isoenzyme B-6 is located in cell walls, it seems plausible that this isoenzyme may be involved in the insolubilization of phenylpropanoid precursors in muro. These results lend weight to the biochemical evidence for supporting the existence of an oxidative competitive sink for phenylpropanoid intermediates of capsaicin biosynthesis, and which probably competes with capsaicin itself to yield lignin-like substances, in the cell wall of Capsicum annuum var. Annuum.