Smith R J, Larson S, Stred S E, Durschlag R P
J Cell Physiol. 1984 Aug;120(2):197-203. doi: 10.1002/jcp.1041200213.
Glutamine is synthesized in skeletal muscle, released to the circulation, and transported to other tissues, where it may provide important substrate for gluconeogenesis, ammoniagenesis, and energy-yielding pathways. With the ultimate goal of delineating the factors that control glutamine production and release by skeletal muscle, we have studied the regulation of two key enzymes, glutamine synthetase and glutaminase, in the L6 line of rat skeletal muscle cells grown in monolayer culture. The cultured myotubes were found to have glutamine synthetase and phosphate-dependent glutaminase activities. Glutamine synthetase activity was increased following incubation (1) in glutamine-free medium (threefold); (2) in medium containing high glutamic acid concentrations (fourfold); and (3) in medium supplemented with dexamethasone (threefold). In each case the increase in glutamine synthetase activity required several hours to reach a maximum and was prevented by cycloheximide, suggesting that the change occurred through increased enzyme biosynthesis. No substances tested were found to affect glutaminase activity. We conclude that glutamine synthetase in cultured skeletal muscle is responsive to substrate, product, and hormonal regulation.
谷氨酰胺在骨骼肌中合成，释放进入循环系统，并转运至其他组织，在这些组织中它可能为糖异生、氨生成及产能途径提供重要底物。为了最终确定控制骨骼肌谷氨酰胺产生和释放的因素，我们研究了单层培养的大鼠骨骼肌L6细胞系中两种关键酶——谷氨酰胺合成酶和谷氨酰胺酶的调节机制。发现培养的肌管具有谷氨酰胺合成酶和磷酸依赖性谷氨酰胺酶活性。在以下培养条件下，谷氨酰胺合成酶活性增加：（1）在无谷氨酰胺培养基中（增加三倍）；（2）在含有高浓度谷氨酸的培养基中（增加四倍）；（3）在添加地塞米松的培养基中（增加三倍）。在每种情况下，谷氨酰胺合成酶活性的增加都需要数小时才能达到最大值，并且被环己酰亚胺抑制，这表明这种变化是通过增加酶的生物合成而发生的。未发现所测试的任何物质会影响谷氨酰胺酶活性。我们得出结论，培养的骨骼肌中的谷氨酰胺合成酶对底物、产物和激素调节有反应。
