Abstract
Factors influencing the inhibition by oxalic acid and its salts(oxalates)of a copper-containing enzyme, tyrosinase, were studied by varying the pH of the reaction mixtures and preincubating the enzyme with the inhibitors under different conditions of the time, pH and temperature. The alleviative effects by long-chain fatty acids, which are known as endogenous activators of the normally-latent enzyme in some organisms, were also examined. The inhibition rate for the tyrosinase activity by oxalates of the same concentration was elevated along with a reduction in the pH values from neutral to mildly acidic. The preincubation treatments time-dependently inactivated the enzyme, and the inhibition was further enhanced by freezing the reaction mixtures at -20°Cat nearly neutral pH. The addition to the reaction mixtures of long-chain fatty acids and their salts significantly alleviated the inhibition, and the more hydrophilic compounds, which can be applied to aqueous media at higher concentrations, exhibited more remarkable effects. These results suggest that the inhibition of tyrosinase by oxalates is influenced by various factors, which may stabilize or remove the chelate linkage between the inhibitors and the functional copper ions in the enzyme molecule.
