The transformation of chlorophenols by lactoperoxidase

The lactoperoxidase-catalyzed transformations of penta-,2,3,4,6-tetra-, 2,4,6-tri-, 2,4-di- and 4-monochlorophenol were followed spectrophotometrically. Apparent stoichiometries of chlorophenol:H2O2 ranged from 1:1 for the tri- and tetrachlorophenol at pH7 to 5:2 for pentachlorophenol at pH 4. The initial velocity (v0) was only slightly influenced by changes in [H2O2] greater then 5 microns. v0 responded to [chlorophenol] according to the empirical expression v0=[lactoperoxidase] . (k1[chlorophenol] + k2[chlorophenol]2). The constant k1 was trichlorophenol, respectively, at pH 7. With the di- and monochlorophenol the solution soon became opaque, and the reaction ceased. The results show that more than one reaction occurs. Some comparisons were also made with horseradish peroxidase A and C. Cetyltrimethylammonium bromide prevented opaqueness, but was shown to be a substrate for lactoperoxidase. Assuming an average concentration of 0.1 microns for H2O2 and pentachlorophenol in man, the metabolic rate becomes 30 ng/h per g of peroxidase-containing tissue, possibly with deposition of the products.