title: Kinetic study of the interaction between frog epidermis tyrosinase and chloride.
abstract: The effect of halide ions on frog epidermis tyrosinase has been characterized with the trypsin-activated enzyme. At pH 7, the order of inhibition is I- greater than Br- greater than Cl- greater than F-. Chloride, the most extensively studied halide, shows a competitive pattern with respect to the substrate, L-DOPA. Inhibition is strongly pH-dependent, with a pKa of 6.12 for the responsible protonatable group. Other kinetic constants are also calculated using a novel approach. The mechanism of interaction between chloride and the enzyme is discussed, and a model is proposed in which chloride interferes the tyrosinase activity by displacing a catalytically important ligand, probably a histidine residue of the side-chain, from the copper at the enzyme-active site.
mesh_terms: D000818:Animals; D001965:Bromides / Q000494:pharmacology; D004156:Catechol Oxidase / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004817:Epidermis / Q000201:enzymology; D005459:Fluorides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007454:Iodides / Q000494:pharmacology; D007700:Kinetics; D007980:Levodopa / Q000494:pharmacology; D008433:Mathematics; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D011893:Rana esculenta; D012867:Skin / Q000201:enzymology*
chemical_list: D001965:Bromides; D002712:Chlorides; D007454:Iodides; D007980:Levodopa; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; D005459:Fluorides