Phosphorylation of MP26, a lens junction protein, is enhanced by activators of protein kinase C.
Phosphorylation of MP26, a lens junction protein, is enhanced by activators of protein kinase C.
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MP26（一种晶状体连接蛋白）的磷酸化可通过蛋白激酶 C 激活剂增强。
DOI：
10.1007/bf01871720
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发表时间：
1989
期刊：
影响因子：
--
通讯作者：
Johnson,RG
中科院分区：
文献类型：
--
作者：
Lampe,PD;Johnson,RG
在激活蛋白激酶C的条件下，被认为在透镜中形成间隙连接通道的蛋白质MP26和其他透镜蛋白被磷酸化。在透镜纤维细胞碎片中用32 P-磷酸盐进行“体内”标记，在细胞匀浆中用32 P-ATP进行标记。在这些实验中，钙和12-O-十四烷酰基佛波醇13-乙酸酯（TPA）都是MP26最大磷酸化所必需的。钙刺激MP26的磷酸化约4倍，TPA与钙导致7倍的增加。如果存在TPA，则1 μ m钙足以进行最大标记。磷酸化氨基酸分析表明，当在TPA和钙存在下在透镜匀浆中磷酸化MP26，然后进行电泳纯化时，约85%磷酸丝氨酸，15%磷酸苏氨酸，没有磷酸酪氨酸。磷酸化发生在MP26的C-末端的细胞质附近。还检查了其他激酶的可能参与。影响cAMP依赖性蛋白激酶的沃尔什抑制剂对TPA介导的磷酸化增加没有影响。在分离膜和添加激酶的研究中，还发现MP26不是钙/钙调素非依赖性蛋白激酶II的底物。因此，蛋白激酶C可以直接磷酸化MP26。
MP26, a protein thought to form gap junctional channels in the lens, and other lens proteins were phosphorylated under conditions that activate protein kinase C. Phosphorylation was detected both in lens fiber cell fragments in an “in vivo” labeling procedure with32P-phosphate and in cell homogenates with32P-ATP. In these experiments, both calcium and 12-O-tetradecanoylphorbol 13-acetate (TPA) were necessary for maximal phosphorylation of MP26. Calcium stimulated the phosphorylation of MP26 approximately fourfold and TPA with calcium led to a sevenfold increase. If TPA was present, 1 μmcalcium was sufficient for maximal labeling. Phosphoamino acid analysis demonstrated approximately 85% phosphoserine, 15% phosphothreonine, and no phosphotyrosine when MP26 was phosphorylated in lens homogenates in the presence of TPA and calcium and then electrophoretically purified. Phosphorylation occurred near the cytoplasmic, C-terminal of MP26. The possible involvement of other kinases was also examined. The Walsh inhibitor, which affects cAMP-dependent protein kinases, had no influence on the TPA-mediated increase in phosphorylation. In studies with isolated membranes and added kinases, MP26 was also found to not be a substrate for calcium/calmodulindependent protein kinase II. Thus, protein kinase C may have phosphorylated MP26 in a direct manner.