The Multiple Forms of Mushroom Tyrosinase

Abstract

Abstract The β-isozyme of mushroom tyrosinase is composed of an equilibrium mixture of polymeric forms with the tetramer predominating. What appears to be a similar equilibrium mixture is also present in fresh mushroom juice. In the purified β-isozyme, under moderate conditions of ionic strength, temperature, and protein concentration, the interconversion among the forms is slow. The equilibrium is shifted toward association to the higher polymers by increasing protein concentration. Dissociation is facilitated by elevated temperature (50°), increased ionic strength (0.2), and the presence of sodium dodecyl sulfate (0.25%). Dissociation of the tetramer is also brought about by 1 mm EDTA and is completely reversed by the presence of 1 mm Ca++. Certain chemical modifications of the enzyme such as succinylation, acetylation, or iodination are accompanied by dissociation. Band III of gel electrophoresis is identified with the tetramer, and the other prominent bands, I-Ia, II, and V, are tentatively identified as monomer, dimer, and octamer, respectively.