Pereira M E, Wilk S
Mount Sinai School of Medicine of CUNY, New York 10029.
Arch Biochem Biophys. 1990 Nov 15;283(1):68-74. doi: 10.1016/0003-9861(90)90613-4.
The multicatalytic proteinase complex (MPC) constitutes a major nonlysosomal proteolytic system that may play an important role in the processing of biologically active peptides and enzymes, as well as in intracellular metabolism. We report that at least two of its subunits of MW 28,800 (S2) and 27,000 (S3) are phosphorylated by a cAMP-dependent protein kinase (PK-A) that copurifies with the complex isolated from bovine pituitaries. The cAMP-induced phosphorylation was time dependent and inhibited by a PK-A inhibitor. Although not an integral part of the complex, PK-A activity was still present even in 1700-fold-purified and apparently homogeneous preparations by criteria of nondissociating polyacrylamide gel electrophoresis. Furthermore, we present evidence that the copurification of the two enzymes is not species or tissue specific, or dependent on a single method of purification. The copurifying kinase was stimulated 10-fold by cAMP (10 microM) and 2- to 3-fold by a peptide substrate of the MPC, but was unaffected by protein kinase C activators (calcium and a phospholipid mixture). These findings suggest that protein phosphorylation may represent a mechanism for regulating the activity of the multicatalytic proteinase complex.
多催化蛋白酶复合体（MPC）构成了一个主要的非溶酶体蛋白水解系统，该系统可能在生物活性肽和酶的加工以及细胞内代谢过程中发挥重要作用。我们报告称，其分子量为28,800（S2）和27,000（S3）的至少两个亚基被一种与从牛垂体中分离出的复合体共纯化的cAMP依赖性蛋白激酶（PK-A）磷酸化。cAMP诱导的磷酸化是时间依赖性的，并被PK-A抑制剂抑制。尽管不是复合体的组成部分，但即使在通过非解离聚丙烯酰胺凝胶电泳标准纯化了1700倍且明显均一的制剂中，PK-A活性仍然存在。此外，我们提供的证据表明，这两种酶的共纯化不是物种或组织特异性的，也不依赖于单一的纯化方法。共纯化的激酶被cAMP（10 microM）刺激了10倍，被MPC的一种肽底物刺激了2至3倍，但不受蛋白激酶C激活剂（钙和磷脂混合物）的影响。这些发现表明，蛋白质磷酸化可能代表了一种调节多催化蛋白酶复合体活性的机制。
