Sheorain V S, Ramakrishna S, Benjamin W B, Soderling T R
J Biol Chem. 1985 Oct 5;260(22):12287-92.
A multifunctional protein kinase, purified from rat liver as ATP-citrate lyase kinase, has been identified as a glycogen synthase kinase. This kinase catalyzed incorporation of up to 1.5 mol of 32PO4/mol of synthase subunit associated with a decrease in the glycogen synthase activity ratio from 0.85 to a value of 0.15. Approximately 65-70% of the 32PO4 was incorporated into site 3 and 30-35% into site 2 as determined by reverse phase high performance liquid chromatography. Release of 32PO4 from the phosphopeptides during automated Edman degradation confirmed the site 3 and 2 assignment. Thermal stability studies established that the phosphorylations of sites 3 and 2 were catalyzed by the same kinase. This multifunctional kinase was distinguished from glycogen synthase kinase-3 on the basis of nucleotide (ATP versus GTP) and protein substrate (glycogen synthase, ATP-citrate lyase, and acetyl-CoA carboxylase) specificities. Since the phosphate contents in glycogen synthase of sites 3 and 2 are altered in diabetes and by insulin administration, the possible involvement of the multifunctional kinase was explored. Glycogen synthase purified from diabetic rabbits was phosphorylated in vitro by this multifunctional kinase at only 10% of the rate compared to synthase purified from control rabbits. Treatment of the diabetics with insulin restored the synthase to a form that was readily phosphorylated in vitro.
一种从大鼠肝脏中纯化出来的多功能蛋白激酶，最初被鉴定为ATP-柠檬酸裂解酶激酶，现已被确定为糖原合酶激酶。这种激酶催化每摩尔合酶亚基掺入多达1.5摩尔的32P，同时糖原合酶活性比从0.85降至0.15。通过反相高效液相色谱法测定，约65%-70%的32P掺入位点3，30%-35%掺入位点2。在自动Edman降解过程中，磷酸肽释放出32P，证实了位点3和位点2的归属。热稳定性研究表明，位点3和位点2的磷酸化是由同一种激酶催化的。这种多功能激酶在核苷酸（ATP与GTP）和蛋白质底物（糖原合酶、ATP-柠檬酸裂解酶和乙酰辅酶A羧化酶）特异性方面与糖原合酶激酶-3不同。由于糖尿病和胰岛素给药会改变糖原合酶中位点3和位点2的磷酸含量，因此对这种多功能激酶的可能作用进行了探索。与从对照兔中纯化的合酶相比，从糖尿病兔中纯化的糖原合酶在体外被这种多功能激酶磷酸化的速率仅为10%。用胰岛素治疗糖尿病患者可使合酶恢复到在体外易于磷酸化的形式。
