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Predicate | Object |
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rdf:type | |
lifeskim:mentions | |
pubmed:issue |
10
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pubmed:dateCreated |
1991-5-1
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pubmed:abstractText |
In aspartate aminotransferase (AspAT), His143 is located within a hydrogen-bonding distance to Asp222 that forms a strong ion pair with the ring nitrogen of the coenzyme, pyridoxal 5'-phosphate (PLP) or pyridoxamine 5'-phosphate (PMP). His143 of Escherichia coli AspAT was replaced by Ala or Asn. The mutant enzyme H143A showed a slight increase in the maximum velocity of the overall transamination reaction between aspartate and 2-oxoglutarate, while H143N AspAT showed a decrease to 60% in the maximum rate of the overall reactions in both directions. In all of the half-transamination reactions with four substrates, aspartate, glutamate, oxalacetate, and 2-oxoglutarate, the catalytic competence as defined by kmax/Kd decreased by 3-18-fold upon replacing His143 by either Ala or Asn. The extent of the decrease varied from one substrate to another; it was largely contributed to by the decrease in affinities for all substrates. The equilibrium constants, [PMP-form] [keto acid]/[( PLP-form] [amino acid]), decreased by over 10-fold upon the mutations at position 143. Both H143A and H143N AspATs exhibited a considerably decreased affinity for 2-methylaspartate, an external-aldimine-forming substrate analogue, yet without appreciable alteration in the affinity for succinate and glutarate, which are non-aldimine-forming analogues. All these findings suggest that, although His143 is not essential for catalysis, it might assist the formation of enzyme-substrate complex.
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pubmed:language |
eng
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pubmed:journal | |
pubmed:citationSubset |
IM
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pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/Aspartate Aminotransferases,
http://linkedlifedata.com/resource/pubmed/chemical/Histidine,
http://linkedlifedata.com/resource/pubmed/chemical/Pyridoxal Phosphate,
http://linkedlifedata.com/resource/pubmed/chemical/Pyridoxamine,
http://linkedlifedata.com/resource/pubmed/chemical/pyridoxamine phosphate
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pubmed:status |
MEDLINE
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pubmed:month |
Apr
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pubmed:issn |
0021-9258
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:day |
5
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pubmed:volume |
266
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
6079-85
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pubmed:dateRevised |
2006-11-15
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pubmed:meshHeading |
pubmed-meshheading:2007566-Aspartate Aminotransferases,
pubmed-meshheading:2007566-Base Sequence,
pubmed-meshheading:2007566-Binding Sites,
pubmed-meshheading:2007566-Catalysis,
pubmed-meshheading:2007566-Circular Dichroism,
pubmed-meshheading:2007566-Escherichia coli,
pubmed-meshheading:2007566-Histidine,
pubmed-meshheading:2007566-Hydrogen-Ion Concentration,
pubmed-meshheading:2007566-Kinetics,
pubmed-meshheading:2007566-Molecular Sequence Data,
pubmed-meshheading:2007566-Mutagenesis, Site-Directed,
pubmed-meshheading:2007566-Pyridoxal Phosphate,
pubmed-meshheading:2007566-Pyridoxamine,
pubmed-meshheading:2007566-Spectrophotometry, Ultraviolet
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pubmed:year |
1991
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pubmed:articleTitle |
The role of His143 in the catalytic mechanism of Escherichia coli aspartate aminotransferase.
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pubmed:affiliation |
Department of Medical Chemistry, Osaka Medical College, Japan.
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pubmed:publicationType |
Journal Article,
Research Support, Non-U.S. Gov't
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