Mechanism of halide-stimulated activity of chloroperoxidase evidence for enzymatic formation of free hypohalous acid.

In acidic solutions, bromide stimulates H2O2 decomposition catalyzed by chloroperoxidase or horseradish peroxidase, altogether similar to stimulation, by chloride and bromide, of H2O2 oxidation by HOCl. Low levels of an ultra-pure NaCl inhibited chloroperoxidase catalatic activity whereas very high concentrations of this salt stimulated the reaction. The stimulation reflects low bromide contamination of the ultra-pure NaCl, which is considerably less than Br levels in most AR grade chloride salts. In all of these systems, bromide functions as a catalyst which is first oxidized to Br2 by HOX (added directly or generated enzymatically), and subsequently regenerated by H2O2 reduction of Br2. These results provide strong support for a dissociable species, most likely HOX, as the first product of chloroperoxidase catalyzed oxidation of Br- and Cl- by H2O2.