The process for the activation of frog epidermis pro-tyrosinase

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Abstract
Purified pro-tyrosinase from epidermis of the frog Rana esculenta ridibunda can be activated in vitro by several proteinases (trypsin, .alpha.-chymotrypsin, Pronase) and by light. Both pro-tyrosinase and tyrosinase are composed of a single type of subunit having pI [isoelectric point] 7.2 and .apprx. MW 68,000 and 62,000, respectively. A peptide of low MW is released as a consequence of the proteolytic activation. Pro-tyrosinase and tyrosinase have different quaternary structures, the proenzyme being a dimer of MW .apprx. 115,000 and the enzyme a tetramer of MW .apprx. 210,000. The activation process was affected by several agents (L-3,4-dihydroxyphenylalanine, urea, formamide) that prevented, partially or totally, the activation of pro-tyrosinase. The activation of pro-tyrosinase seems to be the result of a cleavage of the polypeptide chain that determines changes in tertiary or quaternary structure.