Determination of peroxidative halogenation in mixtures of chloride and bromide

A method for the differentiation of chlorinated and brominated products from peroxidative oxidation of mixtures of the halides is presented. Chlorination or bromination of monochlorodimedone (MCD) by fungal chloroperoxidase (CPO) was measured by loss of MCD absorbance. Although the Vmax was similar for both halides [approximately 0.08 mM (2 min)-1], the apparent Km for chlorination was 10 times greater than that for bromination (5.88 vs 0.67 mM). Chlorination was also quantitated as I3- produced from N-chlorotaurine and I-. The Vmax [0.076 mM (2 min)-1] and apparent Km (6.31 mM) determined by this method agreed with those determined with MCD. Selective reduction by H2O2 of the I-oxidizing potential of N-bromotaurine allowed determination of the brominated product from the difference between the amounts of halogenated MCD and N-chlorotaurine. The brominated product predominated at saturating and at physiologic halide levels. Hence, it is suggested that Br- plays a significant role in halogenation even though in vivo levels of Cl- are equal to or greater than 1000 times those Br-.