KINETICS STUDY OF THE OXIDATION OF 4-TERT-BUTYLPHENOL BY TYROSINASE

The reaction between 4-tert-butylphenol (BuPhOH) and mushroom tyrosina se was investigated by following 4-tert-butyl-ortho-benzoquinone, whos e high stability permits the reaction to be used as a model for the st udy of the monophenolase activity of tyrosinase. The system evolves to a pseudo-steady state through an induction period (tau), the pseudo-s teady-state rate (V-ss) decreasing when the (BuPhOH) concentration inc reases. Increases in enzyme concentration result in a parabolic patter n with V-ss, while tau is shortened. The addition of increasing cataly tic amounts of 4-tert-butylcatechol at the start of the reaction reduc es tau until it is totally abolished, an initial burst being observed at high 6-t-butylatechol concentrations. Initial bursts are also obtai ned at pH 4.5 or lower, indicating a lower affinity of the met-tyrosin ase or oxidized form for the monophenol at low pH. These experimental results can be explained by the reaction mechanism of tyrosinase.