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 − > Br − > CI − > 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 p K A 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.
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