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In molecular biology, Glycoside hydrolase family 14 is a family of glycoside hydrolases. Glycoside hydrolases are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families.〔(Bairoch, A. "Classification of glycosyl hydrolase families and index of glycosyl hydrolase entries in SWISS-PROT". 1999. )〕 This classification is available on the CAZy(http://www.cazy.org/GH1.html) web site,〔(Henrissat, B. and Coutinho P.M. "Carbohydrate-Active Enzymes server". 1999. )〕 and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.〔(CAZypedia, an online encyclopedia of carbohydrate-active enzymes. )〕 Glycoside hydrolase family 14 (CAZY GH_14 ) comprises enzymes with only one known activity; beta-amylase (). A Glu residue has been proposed as a catalytic residue, but it is not known if it is the nucleophile or the proton donor. Beta-amylase is an enzyme that hydrolyzes 1,4-alpha-glucosidic linkages in starch-type polysaccharide substrates so as to remove successive maltose units from the non-reducing ends of the chains. Beta-amylase is present in certain bacteria as well as in plants. Three highly conserved sequence regions are found in all known beta-amylases. The first of these regions is located in the N-terminal section of the enzymes and contains an aspartate which is known to be involved in the catalytic mechanism. The second, located in a more central location, is centred on a glutamate which is also involved in the catalytic mechanism. The 3D structure of a complex of soybean beta-amylase with an inhibitor (alpha-cyclodextrin) has been determined to 3.0A resolution by X-ray diffraction. The enzyme folds into large and small domains: the large domain has a (beta alpha)8 super-secondary structural core, while the smaller is formed from two long loops extending from the beta-3 and beta-4 strands of the (beta alpha)8 fold.〔 The interface of the two domains, together with shorter loops from the (beta alpha)8 core, form a deep cleft, in which the inhibitor binds.〔 Two maltose molecules also bind in the cleft, one sharing a binding site with alpha-cyclodextrin, and the other sitting more deeply in the cleft.〔 ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Glycoside hydrolase family 14」の詳細全文を読む スポンサード リンク
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