Department of Food Science, Whistler Center for Carbohydrate Research, Purdue University, West Lafayette, Indiana 47907, USA.
J Biol Chem. 2012 Sep 14;287(38):31929-38. doi: 10.1074/jbc.M112.351858. Epub 2012 Jul 31.
Starch digestion involves the breakdown by α-amylase to small linear and branched malto-oligosaccharides, which are in turn hydrolyzed to glucose by the mucosal α-glucosidases, maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI). MGAM and SI are anchored to the small intestinal brush-border epithelial cells, and each contains a catalytic N- and C-terminal subunit. All four subunits have α-1,4-exohydrolytic glucosidase activity, and the SI N-terminal subunit has an additional exo-debranching activity on the α-1,6-linkage. Inhibition of α-amylase and/or α-glucosidases is a strategy for treatment of type 2 diabetes. We illustrate here the concept of "toggling": differential inhibition of subunits to examine more refined control of glucogenesis of the α-amylolyzed starch malto-oligosaccharides with the aim of slow glucose delivery. Recombinant MGAM and SI subunits were individually assayed with α-amylolyzed waxy corn starch, consisting mainly of maltose, maltotriose, and branched α-limit dextrins, as substrate in the presence of four different inhibitors: acarbose and three sulfonium ion compounds. The IC(50) values show that the four α-glucosidase subunits could be differentially inhibited. The results support the prospect of controlling starch digestion rates to induce slow glucose release through the toggling of activities of the mucosal α-glucosidases by selective enzyme inhibition. This approach could also be used to probe associated metabolic diseases.
淀粉消化涉及α-淀粉酶将其分解成小的线性和支链麦芽低聚糖，这些麦芽低聚糖随后被黏膜α-葡萄糖苷酶进一步水解为葡萄糖，黏膜α-葡萄糖苷酶包括麦芽糖酶-葡糖苷酶（MGAM）和蔗糖酶-异麦芽糖酶（SI）。MGAM 和 SI 都锚定在小肠刷状缘上皮细胞上，每个酶都包含一个催化的 N-和 C-末端亚基。这四个亚基都具有α-1,4-外切水解葡萄糖苷酶活性，而 SI 的 N-末端亚基在α-1,6 键上具有额外的外切分支活性。抑制α-淀粉酶和/或α-葡萄糖苷酶是治疗 2 型糖尿病的一种策略。我们在这里举例说明了“切换”的概念：对亚基进行差异抑制，以检查对 α-淀粉酶水解淀粉麦芽低聚糖的糖生成的更精细控制，目的是缓慢释放葡萄糖。用四种不同的抑制剂（阿卡波糖和三种硫鎓离子化合物），分别用α-淀粉酶水解的蜡质玉米淀粉（主要由麦芽糖、麦芽三糖和支链α-极限糊精组成）作为底物，对重组 MGAM 和 SI 亚基进行了单独检测。IC50 值表明，这四个α-葡萄糖苷酶亚基可以进行差异抑制。这些结果支持通过选择性酶抑制来调节黏膜α-葡萄糖苷酶的活性来控制淀粉消化速率，从而诱导缓慢释放葡萄糖的前景。这种方法也可用于研究相关的代谢疾病。
