Multiple forms of protyrosinase from Aspergillus oryzae and their mode of activation at pH 3.0

This paper describes the isolation of three molecular forms (I-III) of protyrosinase and catalytically active tyrosinase ( monophenol ,dihydroxyphenylalanine: oxygen oxidoreductase, E.C. 1.14.18.1) from fresh mycelia of Aspergillus oryzae BIR 128 by (NH4)2SO4 fractionation, successive chromatographies and disc-gel electrophoresis. Experimental evidence is presented that purified protyrosinase is contaminated with firmly attached proteinases, and that this contamination may account for both the multiple molecular forms of protyrosinase /tyrosinase and the activation of the proenzyme at acidic pH (2.5-3.0). The activation process of protyrosinase seems to be the result of a cleavage of the polypeptide chain by aspartic proteinase from Aspergillus (EC 3.4.23.6) in the purified protyrosinase preparation. Protyrosinase and tyrosinase have different conformation, different stabilities and some different properties.