Source:http://linkedlifedata.com/resource/pubmed/id/17625266
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| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
1
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| pubmed:dateCreated |
2007-7-12
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| pubmed:abstractText |
Beta-D-Xylosidase from Selenomonas ruminantium is revealed as the best catalyst known (kcat, kcat/Km) for promoting hydrolysis of 1,4-beta-D-xylooligosaccharides. 1H nuclear magnetic resonance experiments indicate the family 43 glycoside hydrolase acts through an inversion mechanism on substrates 4-nitrophenyl- beta-D-xylopyranoside (4NPX) and 1,4-beta-D-xylobiose (X2). Progress curves of 4-nitrophenyl-beta-D-xylobioside, xylotetraose and xylohexaose reactions indicate that one residue from the nonreducing end of substrate is cleaved per catalytic cycle without processivity. Values of kcat and kcat/Km decrease for xylooligosaccharides longer than X2, illustrating the importance to catalysis of subsites -1 and +1 and the lack there of subsite +2. Homology models of the enzyme active site with docked substrates show that subsites beyond -1 are blocked by protein and subsites beyond +1 are not formed; they suggest that D14 and E186 serve catalysis as general base and general acid, respectively. Individual mutations, D14A and E186A, erode kcat and kcat/Km by <103 and to a similar extent for substrates 4NPX and 4-nitrophenyl-alpha-L-arabinofuranoside (4NPA), indicating that the two substrates share the same active site. With 4NPX and 4NPA, pH governs kcat/Km with pKa values of 5.0 and 7.0 assigned to D14 and E186, respectively. kcat(4NPX) has a pKa value of 7.0 and kcat(4NPA) is pH independent above pH 4.0, suggesting that the catalytically inactive, "dianionic" enzyme form (D14-E187-) binds 4NPX but not 4NPA.
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| pubmed:language |
eng
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| pubmed:journal | |
| pubmed:citationSubset |
IM
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| pubmed:chemical | |
| pubmed:status |
MEDLINE
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| pubmed:month |
Apr
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| pubmed:issn |
1559-0291
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| pubmed:author | |
| pubmed:issnType |
Electronic
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| pubmed:volume |
141
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| pubmed:owner |
NLM
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| pubmed:authorsComplete |
Y
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| pubmed:pagination |
51-76
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| pubmed:meshHeading |
pubmed-meshheading:17625266-Catalysis,
pubmed-meshheading:17625266-Enzyme Activation,
pubmed-meshheading:17625266-Enzyme Stability,
pubmed-meshheading:17625266-Selenomonas,
pubmed-meshheading:17625266-Structure-Activity Relationship,
pubmed-meshheading:17625266-Substrate Specificity,
pubmed-meshheading:17625266-Xylosidases
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| pubmed:year |
2007
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| pubmed:articleTitle |
Structure-function relationships of a catalytically efficient beta-D-xylosidase.
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| pubmed:affiliation |
US Department of Agriculture, Fermentation Biotechnology Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, Peoria, IL 61604, USA. jordand@ncaur.usda.gov
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| pubmed:publicationType |
Journal Article
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