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Predicate | Object |
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rdf:type | |
lifeskim:mentions | |
pubmed:issue |
1
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pubmed:dateCreated |
1976-8-23
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pubmed:abstractText |
The binding of indole and indolepropanol phosphate, an analogue of the substrate indoleglycerol phosphate, to the individual alpha and beta2-subunits and to the alpha2beta2-complex of tryptophan synthase was studied by equilibrium dialysis. The use of [14C]indole and indolepropanol [32P]phosphate permitted simultaneous binding studies to be carried out. Competition between indole and indolepropanol phosphate in binding to a particular site was taken as evidence for that site being part of the active site of the alpha-subunit. The binding of indole to the active site of the alpha-subunit is weak (Kd = 18mM). A second distinct site binds indole more strongly (Kd = 1.5 mM) and interacts with the active site indirectly. It is therefore designated an effector site. Furthermore, the binding of indole and/or indolepropanol phosphate appears to stabilize different conformations of the alpha-subunit. The beta2-subunit binds indole only weakly (Kd = 12 mM) to many (n = 10) sites per polypeptide chain. The alpha2beta2-complex retains one or two sites per alphabeta-equivalent of relatively high affinity (Kd = 1.2 mM). The active sites of the component alpha and beta-subunits probably belong to the second class of many (n = 40) sites of low (Kd = 30 mM) affinity for indole. These findings support conclusions from the literature that both bi-substrate reactions involving indole catalyzed by tryptophan synthase and its subunits must follow strictly ordered addition mechanisms with the respective other substrate adding first.
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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 |
0014-2956
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:day |
15
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pubmed:volume |
64
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
313-20
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pubmed:dateRevised |
2007-7-23
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pubmed:meshHeading |
pubmed-meshheading:776615-Binding Sites,
pubmed-meshheading:776615-Escherichia coli,
pubmed-meshheading:776615-Indoles,
pubmed-meshheading:776615-Kinetics,
pubmed-meshheading:776615-Ligands,
pubmed-meshheading:776615-Macromolecular Substances,
pubmed-meshheading:776615-Mathematics,
pubmed-meshheading:776615-Protein Binding,
pubmed-meshheading:776615-Tryptophan Synthase
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pubmed:year |
1976
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pubmed:articleTitle |
The binding of indole to the alpha-subunit and beta2-subunit and to the alpha2beta2-complex of tryptophan synthase from Escherichia coli. Identification of a second indole-binding site on the alpha-subunit.
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pubmed:publicationType |
Journal Article
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