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Type: Journal article
Title: Hydrolysis of (1,4)-beta-D-mannans in barley (Hordeum vulgare L.) is mediated by the concerted action of (1,4)-beta-D-mannan endohydrolase and beta-D-mannosidase
Author: Hrmova, M.
Burton, R.
Biely, P.
Lahnstein, J.
Fincher, G.
Citation: Biochemical Journal, 2006; 399 Part 1(1):77-90
Publisher: Portland Press
Issue Date: 2006
ISSN: 0264-6021
Statement of
Maria Hrmova, Rachel A. Burton, Peter Biely, Jelle Lahnstein and Geoffrey B. Fincher
Abstract: A family GH5 (family 5 glycoside hydrolase) (1,4)-beta-D-mannan endohydrolase or beta-D-mannanase (EC, designated HvMAN1, has been purified 300-fold from extracts of 10-day-old barley (Hordeum vulgare L.) seedlings using ammonium sulfate fractional precipitation, followed by ion exchange, hydrophobic interaction and size-exclusion chromatography. The purified HvMAN1 is a relatively unstable enzyme with an apparent molecular mass of 43 kDa, a pI of 7.8 and a pH optimum of 4.75. The HvMAN1 releases Man (mannose or D-mannopyranose)-containing oligosaccharides of degree of polymerization 2-6 from mannans, galactomannans and glucomannans. With locust-bean galactomannan and mannopentaitol as substrates, the enzyme has K(m) constants of 0.16 mg x ml(-1) and 5.3 mM and kcat constants of 12.9 and 3.9 s(-1) respectively. Product analyses indicate that transglycosylation reactions occur during hydrolysis of (1,4)-beta-D-manno-oligosaccharides. The complete sequence of 374 amino acid residues of the mature enzyme has been deduced from the nucleotide sequence of a near full-length cDNA, and has allowed a three-dimensional model of the HvMAN1 to be constructed. The barley HvMAN1 gene is a member of a small (1,4)-beta-D-mannan endohydrolase family of at least six genes, and is transcribed at low levels in a number of organs, including the developing endosperm, but also in the basal region of young roots and in leaf tips. A second barley enzyme that participates in mannan depolymerization through its ability to hydrolyse (1,4)-beta-D-manno-oligosaccharides to Man is a family GH1 beta-D-mannosidase, now designated HvbetaMANNOS1, but previously identified as a beta-D-glucosidase [Hrmova, MacGregor, Biely, Stewart and Fincher (1998) J. Biol. Chem. 273, 11134-11143], which hydrolyses 4NP (4-nitrophenyl) beta-D-mannoside three times faster than 4NP beta-D-glucoside, and has an action pattern typical of a (1,4)-beta-D-mannan exohydrolase.
Keywords: Catalytic amine acid; (1; 4)-beta-D-mannan endohydrolase; beta-D-mannosidase; family GH1 and GH5 glycoside hydrolases; Hordeum vulgare; transglycosylation
RMID: 0020061437
DOI: 10.1042/BJ20060170
Appears in Collections:Agriculture, Food and Wine publications

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