Hiraga A, Kikuchi K, Tamura S, Tsuiki S
Eur J Biochem. 1981 Oct;119(3):503-10. doi: 10.1111/j.1432-1033.1981.tb05636.x.
Phosphoprotein phosphatase IA, which represents the major glycogen synthase phosphatase activity in rat liver cytosol, has been purified to apparent homogeneity by chromatography on DEAE-cellulose, histone - Sepharose-4B and Sephadex G-100. The molecular weight of the purified enzyme was 40 000 by gel filtration and 48 000 by sodium dodecyl sulfate gel electrophoresis, Phosphatase IA is therefore a monomeric protein. When treated with 80% ethanol at room temperature, phosphatase IA underwent an inactivation which was totally prevented by 2 mM MgCl2. Catalytically, phosphatase IA has a preference for glycogen synthase D compared with phosphatases IB and II and obligatorily requires Mg2+ or Mn2+ for activity. Maximum activity was attained at 5 mM MgCl2. Since Mg2+ does not activate other phosphoprotein phosphatases in rat liver cytosol, we propose the term 'Mg2+-dependent glycogen synthase phosphatase' for phosphatase IA.
磷蛋白磷酸酶IA是大鼠肝细胞溶胶中主要的糖原合酶磷酸酶活性成分，通过在DEAE - 纤维素、组蛋白 - 琼脂糖 - 4B和葡聚糖凝胶G - 100上进行层析，已纯化至表观均一。通过凝胶过滤法测得纯化酶的分子量为40000，通过十二烷基硫酸钠凝胶电泳法测得为48000，因此磷酸酶IA是一种单体蛋白。在室温下用80%乙醇处理时，磷酸酶IA会失活，而2 mM氯化镁可完全防止这种失活。在催化方面，与磷酸酶IB和II相比，磷酸酶IA对糖原合酶D具有偏好性，并且其活性必然需要镁离子或锰离子。在5 mM氯化镁时达到最大活性。由于镁离子不会激活大鼠肝细胞溶胶中的其他磷蛋白磷酸酶，我们建议将磷酸酶IA称为“镁离子依赖性糖原合酶磷酸酶”。
