Mehrani H, Storey K B
Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada.
Arch Biochem Biophys. 1993 Oct;306(1):188-94. doi: 10.1006/abbi.1993.1499.
Three forms of alpha-glucosidase were separable in trout liver by DE-52 chromatography, isoelectrofocusing, and gel filtration. Two forms showed acid pH optima, hydrolyzed glycogen, maltose, and 4-methylumbelliferyl alpha-glucoside, and were associated with the lysosomes. The third enzyme form was largely associated with microsomes and was present in the highest activity; it showed a neutral pH optimum and did not hydrolyze glycogen. Molecular weights were 181 +/- 2, 130 +/- 1.5, and 365 +/- 3 kDa for the acid types I and II and the neutral enzyme, respectively. Maximal activities and kinetic and physical properties of the three enzymes were compared in liver samples from control, resting fish versus fish that underwent exhaustive swimming exercise. The properties of liver acid alpha-glucosidase type I changed significantly in response to exercise; maximal activity increased by 80% and Km values for both glycogen and maltose dropped by 50% in exercised, versus control, fish. Under the same exercise condition, liver glycogen phosphorylase a activity also increased 4.4-fold. These changes in alpha-glucosidase type I are consistent with an activation of the enzyme, in parallel with phosphorylase activation, under physiological stress conditions that promote glycogenolysis and glucose export from liver. These results are, we believe, the first demonstration of the activation of the glucosidic route of glycogenolysis in response to a physiological stress and suggest that the glucosidic route has a significant role to play in complementing the phosphorolytic pathway in the metabolic response by liver to the fuel demands of working muscle.
通过DE-52柱层析、等电聚焦和凝胶过滤法，可将鳟鱼肝脏中的三种α-葡萄糖苷酶形式分离出来。其中两种形式的酶在酸性pH条件下具有最佳活性，能水解糖原、麦芽糖和4-甲基伞形酮基α-葡萄糖苷，且与溶酶体相关。第三种酶形式主要与微粒体相关，活性最高；其在中性pH条件下具有最佳活性，不能水解糖原。酸性I型和II型酶以及中性酶的分子量分别为181±2 kDa、130±1.5 kDa和365±3 kDa。比较了来自对照静止鱼和进行了极限游泳运动的鱼的肝脏样本中这三种酶的最大活性、动力学和物理性质。I型肝脏酸性α-葡萄糖苷酶的性质在运动后发生了显著变化；与对照鱼相比，运动鱼的最大活性增加了80%，糖原和麦芽糖的Km值均下降了50%。在相同运动条件下，肝脏糖原磷酸化酶a的活性也增加了4.4倍。I型α-葡萄糖苷酶的这些变化与该酶的激活相一致，与磷酸化酶的激活同时发生，处于促进糖原分解和肝脏葡萄糖输出的生理应激条件下。我们认为，这些结果首次证明了糖原分解的糖苷途径在生理应激下被激活，并表明糖苷途径在补充肝脏代谢反应中磷酸解途径以满足工作肌肉对燃料的需求方面具有重要作用。
