4-Substituted Resorcinols (Sulfite Alternatives) as Slow-Binding Inhibitors of Tyrosinase Catecholase Activity

A kinetic study of the inhibition of mushroom tyrosinase catecholase activity by 4-substituted resorcinols has been made. The results obtained show that 4-substituted resorcinols inhibit tyrosinase in a nonclassical manner and that the inhibition is characterized by a long transient phase. Progress curves of enzymatic reaction in the presence of inhibitor show a progressive decrease in initial velocity followed by a constant steady-state rate. Both the initial and the constant rates decreased with increasing concentrations of inhibitor. Kinetic data obtained correspond to those for a postulated mechanism involving rapid formation of an enzyme−inhibitor complex that subsequently undergoes a relatively slow reversible reaction. The kinetic parameters characterizing this time-dependent inhibition were evaluated by means of nonlinear regression of the product accumulation curves.