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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 24, Number 5
BKCSDE 24(5)
May 20, 2003 

The pH Studies of Recombinant Acetohydroxy Acid Synthase from Tobacco
Jung-Do Choi, Bok-Hwan Kim, Moon-Young Yoon
Acetohydroxy acid synthase, pH study, Tobacco
The pH dependence of the kinetic parameters of recombinant acetohydroxy acid synthase catalyzed reaction was determined in order to obtain information about the chemical mechanism, particularly acid-base chemistry. The maximum velocity and V/K for pyruvate were bell-shaped with estimated pK values of 6.5-6.7 and 8.6- 8.9, respectively. The maximum velocity and V/K for 2-ketobutyrate were also bell-shaped with estimated pK values of 6.6-7.0 and 8.4-8.6. The pH dependence of 1/Ki for 3-bromopyruvate, a competitive inhibitor of pyruvate, was also bell-shaped, giving pK values almost identical with those obtained for pyruvate. Since the same pK values were observed in the pKi 3-bromopyruvate, V/K pH profiles and Vmax profiles, both enzyme groups must be in their optimum protonation state for efficient binding of reactants. These results reflect that two enzyme groups are necessary for binding of substrate and/or catalysis.
627 - 632
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