Protease-activated protein kinase C in rat liver.

E Hashimoto, H Yamamura
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Abstract

In regenerating rat liver, an elevated protein kinase activity was detected which phosphorylated ribosomal protein S6 and histones. The properties of this enzyme were closely similar with those of protease-activated protein kinase C with Mr 45,000. During the study of the mechanism of proteolytic activation, type III protein kinase C (encoding alpha-sequence) was shown to be subjected to limited proteolysis by trypsin-like protease and converted to protein kinase M in ionic strength- and pH-dependent manner. This reaction was stimulated in the presence of Ca2+ and phospholipid under slightly higher ionic strength condition than physiological level (greater than 140 mM NaCl) and alkaline pH (7.5-8.0). These results suggest that activation of Na+/H+ exchanger in plasma membrane may trigger this type of proteolytic activation of protein kinase C. In addition to protein kinase M, another type of protease-activated kinase with Mr 80,000 was detected when limited proteolysis of protein kinase C was performed on inactive form of this enzyme (in the absence of either Ca2+ or phospholipid or both activators) under lower ionic strength condition. The molecular mass of this active enzyme was slightly smaller (approximately 200) than that of native protein kinase C. However, it is not clear at this time whether this small fragment was released from amino-terminal or carboxy-terminal domain to make protein kinase C partially active in the absence of Ca2+ and phospholipid. Although it has been proposed that proteolytic degradation of protein kinase C is involved in down regulation of this enzyme, the physiological significance of these two types of protease-activated forms of protein kinases in liver has remained obscure.

大鼠肝脏蛋白酶活化蛋白激酶C。
在再生大鼠肝脏中,检测到磷酸化核糖体蛋白S6和组蛋白的蛋白激酶活性升高。该酶的性质与蛋白酶活化蛋白激酶C的性质非常相似,Mr为45000。在蛋白水解激活机制的研究中,III型蛋白激酶C(编码α -序列)被胰蛋白酶样蛋白酶有限地水解,并以离子强度和ph依赖的方式转化为蛋白激酶M。在离子强度略高于生理水平(大于140 mM NaCl)和碱性pH(7.5 ~ 8.0)的条件下,Ca2+和磷脂的存在刺激了该反应。这些结果表明,质膜上Na+/H+交换器的激活可能会触发蛋白激酶C的这种蛋白水解激活。除了蛋白激酶M外,在低离子强度条件下,当对蛋白激酶C的失活形式(在没有Ca2+或磷脂或两种活化剂的情况下)进行有限的蛋白水解时,检测到另一种类型的蛋白酶活化激酶,其Mr为80,000。该活性酶的分子质量比天然蛋白激酶C略小(约200)。然而,目前尚不清楚这个小片段是从氨基端还是羧基端释放的,从而使蛋白激酶C在缺乏Ca2+和磷脂的情况下具有部分活性。虽然已经提出蛋白激酶C的蛋白水解降解参与了该酶的下调,但这两种类型的蛋白酶激活形式的蛋白激酶在肝脏中的生理意义仍然不清楚。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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