Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/13424
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Type: Journal article
Title: Substrate binding and catalytic mechanism of a barley b-D-glucosidase (1,4)-b-D-glucan exohydrolase
Author: Hrmova, M.
MacGregor, E.
Biely, P.
Stewart, R.
Fincher, G.
Citation: Journal of Biological Chemistry, 1998; 273(18):11134-11143
Publisher: AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
Issue Date: 1998
ISSN: 0021-9258
1083-351X
Abstract: A beta-glucosidase, designated isoenzyme betaII, from germinated barley (Hordeum vulgare L.) hydrolyzes aryl-beta-glucosides and shares a high level of amino acid sequence similarity with beta-glucosidases of diverse origin. It releases glucose from the non-reducing termini of cellodextrins with catalytic efficiency factors, kcat/Km, that increase approximately 9-fold as the degree of polymerization of these substrates increases from 2 to 6. Thus, the enzyme has a specificity and action pattern characteristic of both beta-glucosidases (EC 3.2.1.21) and the polysaccharide exohydrolase, (1,4)-beta-glucan glucohydrolase (EC 3.2.1.74). At high concentrations (100 mM) of 4-nitrophenyl beta-glucoside, beta-glucosidase isoenzyme betaII catalyzes glycosyl transfer reactions, which generate 4-nitrophenyl-beta-laminaribioside, -cellobioside, and -gentiobioside. Subsite mapping with cellooligosaccharides indicates that the barley beta-glucosidase isoenzyme betaII has six substrate-binding subsites, each of which binds an individual beta-glucosyl residue. Amino acid residues Glu181 and Glu391 are identified as the probable catalytic acid and catalytic nucleophile, respectively. The enzyme is a family 1 glycoside hydrolase that is likely to adopt a (beta/alpha)8 barrel fold and in which the catalytic amino acid residues appear to be located at the bottom of a funnel-shaped pocket in the enzyme.
Keywords: Hordeum; beta-Glucosidase; Glucan 1,4-beta-Glucosidase; Peptide Mapping; Crystallography, X-Ray; Amino Acid Sequence; Substrate Specificity; Kinetics; Catalysis; Models, Chemical; Molecular Sequence Data
RMID: 0030003711
DOI: 10.1074/jbc.273.18.11134
Appears in Collections:Agriculture, Food and Wine publications

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