Kinetics of Tyrosine Oxidation by Crude Tyrosinase Preparations from Neurospora crassa. ∗

Summary

1. Oxidation of tyrosine by crude enzyme extracts of Neurospora mycelium, as measured by spectrophotometric determination of dopachrome formation, follows a course similar to that exhibited by purified tyrosinase. 2. The reaction exhibits conventional Michaelis-Menten kinetics with a pH optimum of 7.4. 3. Each mole of tyrosine utilized during the reaction is converted into a mole of dopachrome, thus demonstrating that no enzymatic systems utilizing tyrosine other than tyrosinase are present, and that the use of crude extracts and spectrophotometric methods is justified. 4. The induction period exhibited during the oxidation of tyrosine by the crude extracts results from both the production of catalytic amounts of dihydroxyphenols and conversion of protyrosinase to tyrosinase.