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Abstract
Heme‐containing haloperoxidases (heme haloperoxidases) catalyze peroxide‐dependent oxidation of halide ions to hypohalite ions. Nonheme haloperoxidases catalyze peroxidation of alkyl acids to peroxyacids that subsequently oxidize halide ions to hypohalite ions. Hypohalite ions react with kojic acid spontaneously with concomitant production of fluorescence. This reaction was examined for suitability in assaying heme and nonheme haloperoxidase activities spectrofluorometrically. Heme haloperoxidases were assayed directly from hypohalite generation whereas nonheme enzymes were assayed by coupling peroxyacid formation to bromide ion oxidation. Peroxidation of kojic acid by chloroperoxidase and myeloperoxidase did not require halide ions and was not increased upon their addition, demonstrating that haloperoxidase activity was not distinguished from the classical peroxidase‐like activity of these enzymes. Addition of bromide ions to specimens of nonheme haloperoxidase, however, resulted in increased rates of fluorescence generation, indicative of the presence of distinct peroxidase and haloperoxidase enzymes. The heme poison sodium azide inhibited chloroperoxidase, myeloperoxidase, and horseradish peroxidase activities totally but inhibited only a portion of nonheme haloperoxidase activity, verifying that the last specimen was contaminated with heme‐containing peroxidase. Results show the utility of kojic acid for fluorometrically measuring haloperoxidase activity, particularly that of the nonheme enzyme.