The influence of dexamethasone disodium phosphate on the regeneration of corneal endothelium in vitro

Abstract

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 pH 7 to 5:2 for pentachlorophenol at pH 4. The initial velocity (ν0) was only slightly influenced by changes in [H2O2] ⩾ 5 μM. ν0 responded to [chlorophenol] according to the empirical expression ν0 = [lactoperoxidase]·(k1[chlorphenol] + k2[chlorophenol]2). The constant k1 was found to be 5.8 · 105, 1.8 · 106, 1.9 · 106 M−1 · s−1 for the protonated forms of penta-, tetra- and 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 μM for H2O2 and pentachlorophenol in man, the metabolic rate becomes 30 ng/h per g peroxidase-containing tissue, possibly with deposition of the products.