Reactivity of Oxytyrosinase toward Substrates

An oxygenated tyrosinase (T'') is formed by addition of H2O2 to resting mushroom enzyme (Jolley, R. L., Jr., Evans, L. H. & Mason, H. S. (1971) The Second International Symposium on Oxidases and Redox Systems, Memphis, Tennessee, in press; (1972) Biochem. Biophys. Res. Commun. 46, 878). The reactivity of T'' toward monophenolic tyrosinase substrates was investigated by the stopped flow method. The first-order rate constants for T'' disappearance in the presence of p-hydroxybenzaldehyde and p-hydroxybenzoate were about 0.5 and 0.3 s-1, respectively. These rates were sufficiently large to support the over-all enzyme-catalyzed reactions and were not affected by H2O2 concentrations within the concentration ranges examined. T'' appears to be the first oxygenated intermediate detected with a copper oxidase.