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首页> 外文期刊>Biochemistry >Effects of oligosaccharide binding on glycogen debranching enzyme activity and conformation.
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Effects of oligosaccharide binding on glycogen debranching enzyme activity and conformation.

机译：寡糖结合对糖原脱支酶活性和构象的影响。

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摘要

Glycogen debranching enzyme contains two catalytic activities (4-alpha-glucanotransferase and amylo-1,6-glucosidase) on its single polypeptide chain, and they are affected differently by the binding of oligosaccharides. Glucose, maltose, and maltotriose are competitive inhibitors of the amylo-1,6-glucosidase activity measured by the hydrolysis of alpha-glucosyl fluoride, whereas saccharides with four or more glucose units are activators of the same activity, showing apparent "uncompetitive" kinetics. This suggests that they do not bind until the alpha-glucosyl fluoride is bound. In either case the potency of the effect increases with the length of the oligosaccharide chain. On the other hand, all oligosaccharides tested (maltose to maltohexaose, alpha-cyclodextrin, and beta-cyclodextrin) are competitive inhibitors of the transferase activity and also cause a decrease in the intrinsic fluorescence, both functions again increased by chain length, thus indicating that these saccharides do bind to the freeenzyme. These interesting results can be reconciled if the extended main chain resulting from the transferase reaction has to be reoriented into a different binding mode in order to position the alpha-1,6-linked side-chain glucose into the correct position for the glucosidase reaction. Therefore, activating oligosaccharides behave kinetically as if they had not been previously bound. It is concluded that the main chain of the natural limit dextrin substrate has a different mode of binding for the two catalytic reactions in order to position properly first the maltotetraosyl side chain in the transferase catalytic site and then the glucosyl side chain in the glucosidase catalytic site.(ABSTRACT TRUNCATED AT 250 WORDS)
机译：糖原解支酶在其单条多肽链上具有两个催化活性（4-α-葡糖基转移酶和1,6-淀粉葡萄糖苷酶），寡糖的结合对它们的影响不同。葡萄糖，麦芽糖和麦芽三糖是通过α-葡萄糖基氟化物的水解测定的淀粉1,6-葡萄糖苷酶活性的竞争性抑制剂，而具有四个或更多葡萄糖单元的糖是相同活性的活化剂，显示出明显的“非竞争性”动力学。这表明它们直到结合了α-葡糖基氟化物才结合。在这两种情况下，其效果均随着寡糖链长度的增加而增加。另一方面，所有测试的低聚糖（麦芽糖到麦芽六糖，α-环糊精和β-环糊精）都是转移酶活性的竞争性抑制剂，并且还导致固有荧光的降低，两种功能都随着链长的增加而增加，从而表明这些糖确实与自由酶结合。如果必须将由转移酶反应产生的延伸的主链重新定向为不同的结合模式，以便将α-1,6-连接的侧链葡萄糖定位到葡萄糖苷酶反应的正确位置，则可以使这些有趣的结果一致。因此，活化的寡糖在动力学上表现得好像它们以前没有被结合。结论是，天然极限糊精底物的主链对于两种催化反应具有不同的结合模式，以便首先将麦芽四糖基侧链正确地定位在转移酶催化位点中，然后将葡糖基侧链正确地定位在葡糖苷酶催化位点中。 （摘要以250字截断）

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