Camici M, DePaoli-Roach A A, Roach P J
J Biol Chem. 1982 Sep 10;257(17):9898-901.
Rabbit liver glycogen synthase have been purified close to apparent homogeneity in a form dependent on glucose-6-P for full activity. From analyses of the purified enzyme by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, some five polypeptides, apparent molecular weights in the range 79,000 to 90,000, correlated with enzyme activity. The relative abundance of the species varied in different preparations but enzyme could be prepared that was composed almost entirely of a 90,000-dalton polypeptide. Treatment of such enzyme with trypsin generated smaller polypeptides in the sequence 90,000 leads to 85,000 leads to 82,000 leads to 80,000; concomitantly, the enzyme was activated when assayed either in the presence or absence of glucose-6-P. Tryptic proteolysis caused as much as a 16-fold increase in Vmax and a 20-fold increase in the concentration of its substrate, UDP-glucose, necessary for half-maximal activity. The concentration of the activator, glucose-6-P, needed for half-maximal stimulation was decreased 3.5-fold. We propose that rabbit liver glycogen synthase in a glucose-6-P-dependent form has a subunit of apparent molecular weight approximately 90,000, larger than previously reported, and that the enzyme is sensitive to proteolytic degradation.
兔肝糖原合酶已被纯化至接近表观均一性，其完全活性依赖于6-磷酸葡萄糖。通过在十二烷基硫酸钠存在下进行聚丙烯酰胺凝胶电泳分析纯化的酶，发现约有五种多肽，表观分子量在79,000至90,000之间，与酶活性相关。不同制备物中这些多肽的相对丰度有所不同，但可以制备出几乎完全由90,000道尔顿多肽组成的酶。用胰蛋白酶处理这种酶会产生分子量依次为90,000、85,000、82,000和80,000的较小多肽；同时，无论在有无6-磷酸葡萄糖的情况下进行测定，该酶均被激活。胰蛋白酶解导致最大反应速度（Vmax）增加多达16倍，其底物尿苷二磷酸葡萄糖（UDP-葡萄糖）达到最大活性一半时所需的浓度增加20倍。达到最大刺激作用一半时所需的激活剂6-磷酸葡萄糖的浓度降低了3.5倍。我们提出，依赖于6-磷酸葡萄糖的兔肝糖原合酶具有一个表观分子量约为90,000的亚基，该分子量比先前报道的值大，并且该酶对蛋白水解降解敏感。
