The synthesis and activity of tyrosinase during development of the frog Rana pipiens

We have established by radioimmunoprecipitation that tyrosine-DOPA oxidase (TDO, tyrosinase) EC 1.14.18.1] is first synthesized by frog embryos at the early neurula stage soon after embryonic induction of the neural plate by the underlying chordamesoderm. The DOPA moiety of the enzyme, at the time of its first appearance, is almost inactive enzymatically and can be activated by mild proteolysis (with trypsin). A very large increase in the amount of active DOPA oxidizing enzyme (without trypsinization) is observed at hatching (stage 21), and this is accompanied by melanin deposition in pigment cells. The tyrosine moiety of the enzyme is also partially inactive at the time of first synthesis, but the ratio of active to inactive enzyme remains approximately constant throughout early development. DOPA decarboxylase enzymatic activity is first detected at neurula stage, and this activity is accompanied by the first appearance of catechol amines.