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| [[Image:1pb3.jpg|left|200px]] | | {{Seed}} |
| | [[Image:1pb3.png|left|200px]] |
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| {{STRUCTURE_1pb3| PDB=1pb3 | SCENE= }} | | {{STRUCTURE_1pb3| PDB=1pb3 | SCENE= }} |
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| '''Sites of binding and orientation in a four location model for protein stereospecificity.'''
| | ===Sites of binding and orientation in a four location model for protein stereospecificity.=== |
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| ==Overview==
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| The stereospecificity of the enzyme isocitrate dehydrogenase was examined by steady-state kinetics and x-ray crystallography. The enzyme has the intriguing property that the apoenzyme in the absence of divalent metal showed a selectivity for the inactive l-enantiomer of the substrate isocitrate, whereas the enzyme containing magnesium showed selectivity for the physiologically active d-enantiomer. The hydrogen atom on the C2 carbon that is transferred during the reaction was, in both the d- and l-isocitrate complexes, in an orientation very close to that expected for delivery of a hydride ion to the cosubstrate NADP+. The beta-carboxylate that is eliminated as a CO2 molecule during the reaction occupied the same site on the protein in both the d- and l-isocitrate complexes. In addition, the C3 carbon was in the same protein site in both the d- and l-enantiomers. Only the fourth group, the OH atom, was in a very different position in the apo enzyme and in the metal-containing complexes. A four-location model is necessary to explain the enantiomeric specificity of IDH in contrast to the conventional three-point attachment model. The thermodynamic and kinetic ramifications of this model are explored.
| | The line below this paragraph, {{ABSTRACT_PUBMED_10902579}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 10902579 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_10902579}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Isocitrate dehydrogense,idh]] | | [[Category: Isocitrate dehydrogense,idh]] |
| [[Category: Stereospecificity]] | | [[Category: Stereospecificity]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 04:53:46 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 29 06:29:33 2008'' |
