Stereochemical studies of D-glucal hydration by alpha-glucosidases and exo-alpha-glucanases: indications of plastic and conserved phases in catalysis by glycosylases.
Stereochemical studies of D-glucal hydration by alpha-glucosidases and exo-alpha-glucanases: indications of plastic and conserved phases in catalysis by glycosylases.
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α-葡萄糖苷酶和外切-α-葡聚糖酶对 D-葡萄糖水合的立体化学研究：糖基酶催化中可塑相和保守相的迹象。
DOI：
10.1021/bi00405a025
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发表时间：
1988
期刊：
影响因子：
2.9
通讯作者：
Hehre,EJ
中科院分区：
文献类型：
--
作者：
Chiba,S;Brewer,CF;Okada,G;Matsui,H;Hehre,EJ
Seiya千叶，1 Curtis F. Brewer，Gentaro Okada，§ Hirokazu Matsui，11和Edward J. Hehre** 微生物学和免疫学系以及分子药理学系，Albert Einstein医学院，1300 Morris Park Avenue，布朗克斯，纽约？0461接收日期：1987年9月16日;修订版手册接收日期：1987年11月19日摘要：发现来自尼日尔曲霉、猪血清、未发芽的大米、荞麦和甜菜种子（但不来自啤酒酵母或蜜蜂）的葡糖苷酶催化D-葡糖醛的水合。每种反应性葡糖苷酶，与D-葡糖醛在D2 G中孵育，显示从其表面上方质子化（氘化）该前手性底物，即从与质子化α D-糖苷底物所假设的方向相反的方向。与此同时，发现由在D2 G中足够快速地起作用以确定产物构型的三种-葡糖苷酶催化的D-葡糖醛水合产生与从-D-糖苷底物产生的D-葡萄糖相同的特定（a-）构型的2-脱氧-D-葡萄糖。这些发现实质上扩展了早期报道的由一种（热带假丝酵母）α-葡萄糖苷酶制剂水合D-葡萄糖的结果。与其他最近的结果一起，他们表明，α-葡糖苷酶（以及可能一般的糖基化酶）的催化过程可能包括两个单独的和单独控制的部分，即，与底物质子化有关的“塑性”相和与产物构型的产生有关的与底物无关的“保守”相。与葡糖苷酶相反，发现三种“转化”外切-α-葡聚糖酶（球形节杆菌葡糖葡聚糖酶;雪根霉和多变拟青霉葡糖淀粉酶）从其Si面以下质子化D-葡糖醛。此外，而D-葡糖醛水合酶的催化作用被过量底物强烈抑制，而外切葡聚糖酶的促进作用没有表现出可检测到的底物抑制。
Seiya Chiba, 1 Curtis F. Brewer, Gentaro Okada, § Hirokazu Matsui, 11 and Edward J. Hehre** Department of Microbiology and Immunology and Department of Molecular Pharmacology, Albert EinsteinCollege of Medicine, 1300 Morris Park Avenue, Bronx, New York¡ 0461 Received September 16, 1987; Revised Manuscript Received November 19, 1987 abstract:-Glucosidases from Aspergillus niger, pigserum, ungerminated rice, buckwheat, and sugar beet seeds (but not from brewers’ yeast or honeybee) were found to catalyze the hydration of D-glucal. Each reactive-glucosidase, incubated with D-glucal in D2G, was shown to protonate (deuteriate) this prochiral substrate from above its re face, ie, from a direction opposite that assumed for protonating aD-glucosidic substrates. At the same time, D-glucal hydration catalyzed by three of the-glucosidases that acted rapidly enough in D2G to determine product configuration was found to yield 2-deoxy-D-glucose of the same specific (a-) configuration as the D-glucose produced from-D-glucosidic substrates. These findings substantially extend those reported earlierfor the hydration of D-glucalby one (Candida tropicalis) a-glucosidase preparation. Together with other recent results, they suggest that the process of catalysis by a-glucosidases (and perhaps glycosylases in general) may comprise two separate and separately controlled parts, namely, a “plastic” phase concerned with substrate protonation and a substrate-unrelated “conserved” phase concerned with the creation of product configuration. In contrast to the-glucosidases, three “inverting" exo-a-glucanases (Arthrobacter globiformis glucodextranase; Rhizopus niveus and Paecilomyces varioti glucoamylase) were found to protonate D-glucal from below its si face. Further, whereas the catalysis of D-glucal hydration by the-glucosidases was intensively inhibited by excess substrate, that promotedby the exo-glucanases showed no detectable substrate inhibition.