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Chemical transformation is not rate-limiting in the reaction catalyzed by Escherichia coli 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase

  1. Author:
    Li, Y.
    Gong, Y. C.
    Shi, G. B.
    Blaszczyk, J.
    Ji, X. H.
    Yan, H. G.

  2. Author Address

    Michigan State Univ, Dept Biochem & Mol Biol, E Lansing, MI 48824 USA Michigan State Univ, Dept Biochem & Mol Biol, E Lansing, MI 48824 USA Natl Canc Inst, Macromol Crystallog Lab, Ft Detrick, MD 21702 USA Yan HG Michigan State Univ, Dept Biochem & Mol Biol, E Lansing, MI 48824 USA
    1. Year: 2002
  2. Journal: Biochemistry
    1. 41
    2. 27
    3. Pages: 8777-8783
  4. Type of Article: Article
  1. Abstract:

    6-Hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) catalyzes the transfer of pyrophosphate from ATP to 6- hydroxymethyl-7,8-dihydropterin (HMDP). Because HPPK is essential for microorganisms but is absent from human and animals, the enzyme is an excellent target for developing antimicrobial agent. Thermodynamic analysis shows that Mg2+ is important not only for the binding of nucleotides but also for the binding of HMDP. Transient kinetic analysis shows that a step or steps after the chemical transformation are rate- limiting in the reaction catalyzed by HPPK. The pre-steady- state kinetics is composed of a burst phase and a steady-state phase. The rate constant for the burst phase is similar to50 times larger than that for the steady-state phase. The latter is very similar to the k(cat) value measured by steady-state kinetics. A set of rate constants for the individual steps of the HPPK-catalyzed reaction has been determined by a combination of stopped-flow and quench-flow analyses. These results form a thermodynamic and kinetic framework for dissecting the roles of active site residues in the substrate binding and catalysis by HPPK.

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