Hiraga A, Tamura S, Kikuchi K, Tsuiki S
Biochemistry Laboratory, Tohoku University, Miyagi.
J Biochem. 1987 May;101(5):1161-8. doi: 10.1093/oxfordjournals.jbchem.a121980.
To gain more insight into the nature of the substrate specificity of protein phosphatases, four forms of glycogen synthase D were used as substrates for previously characterized protein phosphatases, IA, IB, and II, from rat liver cytosol. The phosphatase activity was measured as the conversion of glycogen synthase D to synthase I. While glycogen synthase isolated from rat liver as the D-form was activated mainly by phosphatase IA, rabbit skeletal muscle glycogen synthase previously phosphorylated in vitro by cyclic AMP-dependent protein kinase or phosphorylase kinase was activated efficiently by phosphatases IA, IB, and II. Glycogen synthase isolated from rabbit skeletal muscle as the D-form, however, was a poor substrate for all three phosphatases. These results suggest that the phosphorylation state as well as the primary structure of synthase D markedly affects the rate of its activation by individual protein phosphatases. A protein phosphatase released from rat liver particulate glycogen, on the other hand, activated all forms of synthase D used here readily and at about the same rate.
为了更深入了解蛋白质磷酸酶底物特异性的本质，使用四种形式的糖原合酶D作为大鼠肝细胞溶质中先前已鉴定的蛋白质磷酸酶IA、IB和II的底物。磷酸酶活性通过糖原合酶D向合酶I的转化来测定。从大鼠肝脏分离得到的D型糖原合酶主要被磷酸酶IA激活，而先前在体外被环磷酸腺苷依赖性蛋白激酶或磷酸化酶激酶磷酸化的兔骨骼肌糖原合酶则被磷酸酶IA、IB和II有效激活。然而，从兔骨骼肌分离得到的D型糖原合酶对所有这三种磷酸酶来说都是较差的底物。这些结果表明，合酶D的磷酸化状态以及一级结构显著影响其被各个蛋白质磷酸酶激活的速率。另一方面，从大鼠肝脏颗粒糖原中释放的一种蛋白质磷酸酶能轻易且以大致相同的速率激活此处使用的所有形式的合酶D。
