Action and Classification of α-Glucosidase

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  • CHIBA Seiya
    Department of' Agricultural Chemistry, Faculty of Agricultrire, Hokkaido University

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  • α‐グルコシダーゼの作用と分類
  • アルファ グルコシダーゼ ノ サヨウ ト ブンルイ

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Description

The difference in the substrate specificities of α-glucosidases [EC 3 .2.1.20] which are classified into three groups is discussed on the basis of the kinetic parameters, Km, k0(= V/e0; e0, enzyme concentration) and k0/Km. The substrate specificities of various α-glucosidases are considered to be distinguishable from one another by examining the action on at least the following five kinds of substrate: p-nitrophenyl- or phenyl-α-glucoside, sucrose, maltose, isomaltose and soluble starch. It is important that the hydrolytic activities toward substrates are compared with the maximum velocity (V) for the cleavage of α-glucosidic bond of nonreducing end. In the "Enzyme Nomenclature, " the distinction between glucoamylase [EC 3.2.1.3] and a group of α-glucosidases capable of attacking α-glucan is not always clear, but glucoamylase and α-glucosidase are definitely different from each other. In the case of glucoamylase, there is a large difference between the ko (or V) values of maltose and those of other maltooligosaccharides. The product is β-glucose. On the other hand, in the case of α-glucosidase, these values are little dependent on the degree of polymerization of glucosyl residues in a series of maltooligosaccharides. The product is α-glucose. Moreover, two kinds of α-glucosidase, isomaltase [EC 3.2.1.10] and sucrase [EC 3.2.1.48], are described in the same "Enzyme Nomenclature." However, α-glucosidase which correspondsexactly to these entries has not yet been reported.

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