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  • enzyme reaction intermediate  (1)
  • 1
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 27 (1997), S. 9-25 
    ISSN: 0887-3585
    Schlagwort(e): CHARMM ; enzyme reaction intermediate ; strong hydrogen bonds ; Marcus formalism analysis ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Citrate synthase forms citrate by deprotonation of acetyl-CoA followed by nucleophilic attack of this substrate on oxaloacetate, and subsequent hydrolysis. The rapid reaction rate is puzzling because of the instability of the postulated nucleophilic intermediate, the enolate of acetyl-CoA. As alternatives, the enol of acetyl-CoA, or an enolic intermediate sharing a proton with His-274 in a “low-barrier” hydrogen bond have been suggested. Similar problems of intermediate instability have been noted in other enzymic carbon acid deprotonation reactions. Quantum mechanical/molecular mechanical calculations of the pathway of acetyl-CoA enolization within citrate synthase support the identification of Asp-375 as the catalytic base. His-274, the proposed general acid, is found to be neutral. The acetyl-CoA enolate is more stable at the active site than the enol, and is stabilized by hydrogen bonds from His-274 and a water molecule. The conditions for formation of a low-barrier hydrogen bond do not appear to be met, and the calculated hydrogen bond stabilization in the reaction is less than the gas-phase energy, due to interactions with Asp-375 at the active site. The enolate character of the intermediate is apparently necessary for the condensation reaction to proceed efficiently. Proteins 27:9-25 © 1997 Wiley-Liss, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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