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

1. 我们在胚胎大鼠脑膜片段中鉴定出三种酪氨酸蛋白激酶（PTK），并分别进行了纯化。其中两种酶与活性血清发生交叉反应，对抗原癌基因src的编码产物pp60^<c-src>，而第三种酶则没有。前两种类型彼此的属性非常相似，都与pp60^<c-src>相同。然而，其中一种仅发生在胚胎和新生儿阶段，因此被命名为pp60^<nc-src>。第三个被发现磷酸化pp60^<c-src>的tyrl -527使其失活，证明它是pp60^<c-src>激酶。从pp60<@1nc-src<@D1和pp60<@D1c-src@>D1激酶在出生后一周内活性最大的发育变化来看，它们可能参与调控神经元细胞的生长和分化。从大鼠脑细胞质中分离到4种高纯度的磷酸酪氨酸蛋白磷酸酶（PTPpase）。其中两种酶仅在大脑中发现，并催化pp60^<c-src>的tyrl -527的去磷酸化，从而诱导转化活性。我们目前正在尝试制备针对PTKs和PTPPases的多克隆和单克隆抗体。有了这些抗体，我们将研究这些酶是如何实质上参与神经元细胞的分化和生长的。

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.