Jiao Y, Shashkin P, Katz A
Department of Surgical Sciences, Karolinska Institutet, Karolinska Hospital, Stockholm, Sweden.
Life Sci. 2001 Jul 13;69(8):891-900. doi: 10.1016/s0024-3205(01)01177-8.
It was recently reported that MnSO4 stimulates glycogen synthase-dependent glucose transfer from UDPglucose into trichloroacetic acid precipitable endogenous glycoproteins (GSMn(T)) in human muscle extracts. To determine the physiologic significance of this reaction, we compared a new GS activity ratio, GSMn(T)/GSH(E) (where GSH(E) represents the usual glucose transfer to ethanol precipitable exogenous glycogen by GS at 7.2 mM glucose 6-phosphate), with the generally used GSL(E)/GSH(E) ratio (where GSL(E) represents glucose transfer at 0.17 mM glucose 6-P concentration). Biopsies were obtained from the quadriceps femoris muscle of healthy subjects at rest, after 40 min of bicycle exercise at approximately 65% of maximal oxygen uptake and after isometric contraction at 2/3 maximal force to fatigue (approximately 1 min). GSMn(T)/GSH(E) increased from 0.012+/-0.002 at rest to 0.054+/-0.008 (P<0.01) after 40 min of bicycle exercise and the increase in GSMn(T) activity was strongly related to the decrease in endogenous glycogen (i.e.. increase in short-chain endogenous glycoproteins) (r=0.90; P<0.05). On the other hand, GSL(E)/GSH(E) did not change significantly after bicycle exercise (rest = 0.49+/-0.04; exercise = 0.58+/-0.08, P>0.05). GSMn(T)/GSH(E) increased from 0.010+/-0.001 at rest to 0.016+/-0.002 (P<0.05) after isometric exercise, whereas GSL(E)/GSH(E) decreased from 0.27+/-0.04 to 0.20+/-0.02 (P<0.05) under corresponding conditions. Last, insulin, which stimulates glycogen synthesis, also increased GSMn(T)/GSH(E) (1.8-fold, P<0.05), as well as GSL(E)/GSH(E) (1.4-fold, P<0.05), in isolated rat soleus muscle. These data indicate that GSMn(T)/GSH(E) is influenced by endogenous substrate availability and covalent modification. Therefore, GSMn(T)/GSH(E) ratio may prove to be a useful alternative to other GS activity ratios that only reflect changes in the phosphorylation state of GS.
最近有报道称，硫酸锰可刺激人肌肉提取物中糖原合酶依赖性的葡萄糖从尿苷二磷酸葡萄糖转移至三氯乙酸可沉淀的内源性糖蛋白（GSMn(T)）中。为确定该反应的生理意义，我们比较了一种新的糖原合酶（GS）活性比值，即GSMn(T)/GSH(E)（其中GSH(E)表示在6 - 磷酸葡萄糖浓度为7.2 mM时，GS将葡萄糖转移至乙醇可沉淀的外源性糖原的常规情况），与常用的GSL(E)/GSH(E)比值（其中GSL(E)表示在6 - 磷酸葡萄糖浓度为0.17 mM时的葡萄糖转移情况）。从健康受试者的股四头肌获取活检样本，分别在静息状态、以约最大摄氧量的65%进行40分钟自行车运动后以及以2/3最大力量进行等长收缩直至疲劳（约1分钟）后采集。GSMn(T)/GSH(E)在静息时为0.012±0.002，自行车运动40分钟后升至0.054±0.008（P<0.01），且GSMn(T)活性的增加与内源性糖原的减少（即短链内源性糖蛋白的增加）密切相关（r = 0.90；P<0.05）。另一方面，自行车运动后GSL(E)/GSH(E)无显著变化（静息时 = 0.49±0.04；运动后 = 0.58±0.08，P>0.05）。等长运动后，GSMn(T)/GSH(E)从静息时的0.010±0.001升至0.016±0.002（P<0.05），而在相应条件下GSL(E)/GSH(E)从0.27±0.04降至0.20±0.02（P<0.05）。最后，刺激糖原合成的胰岛素在离体大鼠比目鱼肌中也使GSMn(T)/GSH(E)增加了1.8倍（P<0.05），同时GSL(E)/GSH(E)增加了1.4倍（P<0.05）。这些数据表明，GSMn(T)/GSH(E)受内源性底物可用性和共价修饰的影响。因此，GSMn(T)/GSH(E)比值可能被证明是其他仅反映GS磷酸化状态变化的GS活性比值的有用替代指标。
