SUMMARY: A single-step procedure was developed which enabled the phenol oxidase of to be recovered in a state of high purity. Ion-exchange chromatography was used to separate the phenol oxidase from an inhibitory protein. Kinetic analysis of the enzyme revealed that it was a tyrosinase (EC. and had a variable ratio of -hydroxylase to -diphenol oxidase activity. The enzyme had a relatively low affinity for oxygen ( of 125 μM) but, compared to other phenol oxidases, a high affinity for its phenolic substrate ( DOPA of 250 μM). The Aspergillus tyrosinase was heterogeneous and appeared to exist in a monomer (mol. wt 1.3 × 10)-tetramer (5.2 × 10) equilibrium. The protein inhibitor was of similar size to the tyrosinase monomer and caused non-competitive inhibition of the enzyme. Both of the tyrosinase activities and the inhibitor had a substantial component of ribonucleic acid. The RNA was not removed from the enzymes or the inhibitor during purification; non-specific complexes may be formed between these proteins and RNA or true ribonucleoproteins may exist. A model is proposed for the physiological function of tyrosinase in under conditions where secondary metabolism does not occur.


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