The Isolation of Tyrosinase from Aspergillus nidulans, Its Kinetic and Molecular Properties and Some Consideration of Its Activity in vivo

Publisher Website
Google Scholar
Abstract
SUMMARY A single-step procedure was developed which enabled the phenol oxidase of Aspergillus nidulans 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. I. 10 .3, I) and had a variable ratio of o-hydroxylase to o-diphenol oxidase activity. The enzyme had a relatively low affinity for oxygen (K, of 125 ,UM) but, compared to other phenol oxidases, a high affinity for its phenolic substrate (K, DOPA of 250 p~). The Aspergillus tyrosinase was heterogeneous and appeared to exist in a monomer (mol. wt 1-3 x 105)-tetramer (5.2 x 105) equilibrium. The protein inhibitor was of similar size to the tyrosinase monomer and caused non-competitive inhibi- tion of the enzyme. Both of the tyrosinase activities and the inhibitor had a sub- stantial 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 A. nidulans under con- ditions where secondary metabolism does not occur.

This publication has 0 references indexed in Scilit: