國家衛生研究院 NHRI:Item 3990099045/3289
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    Please use this identifier to cite or link to this item: http://ir.nhri.org.tw/handle/3990099045/3289


    Title: The roles of Tyr91 and Lys162 in general acid-base catalysis in the pigeon NADP+-dependent malic enzyme
    Other Titles: The roles of Tyr(91) and LyS(162) in general acid-base catalysis in the pigeon NADP(+)-dependent malic enzyme
    Authors: Kuo, CC;Lin, KY;Hsu, YJ;Lin, SY;Lin, YT;Chang, GG;Chou, WY
    Contributors: Institute of Cellular and Systems Medicine
    Abstract: The role of general acid-base catalysis in the enzymatic mechanism of NADP+-dependent malic enzyme was examined by detailed steady-state kinetic studies through site-directed mutagenesis of the Tyr91 and Lys162 residues in the putative catalytic site of the enzyme. Y91F and K162A mutants showed approx. 200- and 27 000-fold decreases in k cat values respectively, which could be partially recovered with ammonium chloride. Neither mutant had an effect on the partial dehydrogenase activity of the enzyme. However, both Y91F and K162A mutants caused decreases in the kcat values of the partial decarboxylase activity of the enzyme by approx. 14- and 3250-fold respectively. The pH-log(kcat) profile of K162A was found to be different from the bell-shaped profile pattern of wild-type enzyme as it lacked a basic pKa value. Oxaloacetate, in the presence of NADPH, can be converted by malic enzyme into L-malate by reduction and into enolpyruvate by decarboxylation activities. Compared with wild-type, the K162A mutant preferred oxaloacetate reduction to decarboxylation. These results are consistent with the function of Lys162 as a general acid that protonates the C-3 of enolpyruvate to form pyruvate. The Tyr91 residue could form a hydrogen bond with Lys162 to act as a catalytic dyad that contributes a proton to complete the enol-keto tautomerization. ? The Authors.
    Date: 2008-05-01
    Relation: Biochemical Journal. 2008 May 1;411(3):467-473.
    Link to: http://dx.doi.org/10.1042/bj20071278
    JIF/Ranking 2023: http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=NHRI&SrcApp=NHRI_IR&KeyISSN=0264-6021&DestApp=IC2JCR
    Cited Times(WOS): https://www.webofscience.com/wos/woscc/full-record/WOS:000255702000001
    Cited Times(Scopus): http://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=42449100760
    Appears in Collections:[Cheng-Chin Kuo] Periodical Articles

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