Lai Yu-Chiang, Stuenaes Jorid Thrane, Kuo Chia-Hua, Jensen Jørgen
Dept. of Physiology, National Institute of Occupational Health, P. O. Box 8149, Dep. N-0033, Oslo, Norway.
Am J Physiol Endocrinol Metab. 2007 Dec;293(6):E1622-9. doi: 10.1152/ajpendo.00113.2007. Epub 2007 Sep 18.
Glycogen content and contraction strongly regulate glycogen synthase (GS) activity, and the aim of the present study was to explore their effects and interaction on GS phosphorylation and kinetic properties. Glycogen content in rat epitrochlearis muscles was manipulated in vivo. After manipulation, incubated muscles with normal glycogen [NG; 210.9 +/- 7.1 mmol/kg dry weight (dw)], low glycogen (LG; 108.1 +/- 4.5 mmol/ kg dw), and high glycogen (HG; 482.7 +/- 42.1 mmol/kg dw) were contracted or rested before the studies of GS kinetic properties and GS phosphorylation (using phospho-specific antibodies). LG decreased and HG increased GS K(m) for UDP-glucose (LG: 0.27 +/- 0.02 < NG: 0.71 +/- 0.06 < HG: 1.11 +/- 0.12 mM; P < 0.001). In addition, GS fractional activity inversely correlated with glycogen content (R = -0.70; P < 0.001; n = 44). Contraction decreased K(m) for UDP-glucose (LG: 0.14 +/- 0.01 = NG: 0.16 +/- 0.01 < HG: 0.33 +/- 0.03 mM; P < 0.001) and increased GS fractional activity, and these effects were observed independently of glycogen content. In rested muscles, GS Ser(641) and Ser(7) phosphorylation was decreased in LG and increased in HG compared with NG. GSK-3beta Ser(9) and AMPKalpha Thr(172) phosphorylation was not modulated by glycogen content in rested muscles. Contraction decreased phosphorylation of GS Ser(641) at all glycogen contents. However, contraction increased GS Ser(7) phosphorylation even though GS was strongly activated. In conclusion, glycogen content regulates GS affinity for UDP-glucose and low affinity for UDP-glucose in muscles with high glycogen content may reduce glycogen accumulation. Contraction increases GS affinity for UDP-glucose independently of glycogen content and creates a unique phosphorylation pattern.
糖原含量和收缩强烈调节糖原合酶（GS）的活性，本研究的目的是探讨它们对GS磷酸化和动力学特性的影响及相互作用。在体内对大鼠肱三头肌的糖原含量进行调控。调控后，在研究GS动力学特性和GS磷酸化（使用磷酸化特异性抗体）之前，将具有正常糖原[NG；210.9±7.1 mmol/kg干重（dw）]、低糖原（LG；108.1±4.5 mmol/kg dw）和高糖原（HG；482.7±42.1 mmol/kg dw）的孵育肌肉进行收缩或静息处理。LG降低而HG增加了GS对UDP-葡萄糖的K(m)值（LG：0.27±0.02＜NG：0.71±0.06＜HG：1.11±0.12 mM；P＜0.001）。此外，GS的分数活性与糖原含量呈负相关（R = -0.70；P＜0.001；n = 44）。收缩降低了UDP-葡萄糖的K(m)值（LG：0.14±0.01 = NG：0.16±0.01＜HG：0.33±0.03 mM；P＜0.001）并增加了GS的分数活性，且这些效应在不考虑糖原含量的情况下均可观察到。在静息肌肉中，与NG相比，LG中GS的Ser(641)和Ser(7)磷酸化降低，HG中则增加。静息肌肉中GSK-3β的Ser(9)和AMPKα的Thr(172)磷酸化不受糖原含量的调节。收缩降低了所有糖原含量下GS的Ser(641)磷酸化。然而，尽管GS被强烈激活，收缩仍增加了GS的Ser(7)磷酸化。总之，糖原含量调节GS对UDP-葡萄糖的亲和力，高糖原含量肌肉中对UDP-葡萄糖的低亲和力可能会减少糖原积累。收缩独立于糖原含量增加GS对UDP-葡萄糖的亲和力并产生独特的磷酸化模式。
