Inhibition of the Tyrosinase Oxidation of One Substrate by Another

The catalytic oxidation of catechol by crude preparations of mushroom tyrosinase was studied by a method yielding data on initial reaction velocities. Graphical analysis of the results suggests that an excess of catechol inhibits its own oxidation by a competitive process, thus accounting for the observed optimum in the substrate concentration. However, added phenol, though itself a substrate, inhibits the enzymatic oxidation of catechol by a process that is neither competitive nor non-competitive, but a mixture of the two types. Mechanisms of this inhibition of the enzyme by a second substrate are discussed in exploring the problem of substrate-substrate inhibition.