Studies on the Physiological Significance of Phosphorylation and Dephosphorylationin the Tyrosine Residues of Brain Proteins

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1. We identified three types of protein tyrosine kinase (PTK) in the membrane fraction of embryonal rat brain, and purified them separately. Two of these enzymes cross-reacted with the actiserum against pp60^<c-src>, an encoding product of protooncogene, src, whereas the third did not. The former two types were quite similar in their properties each other, identical to pp60^<c-src>. However, one of them occurred only in embryonic and neonatal stages, and thus it was named pp60^<nc-src>. The third one was found to phosphorylate Tyr-527 of pp60^<c-src> to inactivate it, demonstrating that it is pp60^<c-src> kinase. From the developmental changes that pp60<@1nc-src<@D1 and pp60<@D1c-src@>D1 kinase showed their maximal activities within a week after birth, it is suggested that they could be involved in the requlation of growth and differentiation of neuronal cells.2. Four types of phosphotyrosine protein phosphatase (PTPpase) were isolated from the cytosolic fraction of rat brain, and highly purified respectively. Two of these enzymes are found only in the brain, and catalyzed the dephosphorylation of Tyr-527 of pp60^<c-src>, which induces the transforming activity.3. We are now attempting preparation of poly- and monoclonal antibodies against PTKs and PTPPases. With these antibodies, we are going to examine how these enzymes are substantially involved in the differentiation and growth of neuronal cells.