Influence of Donor Substrate on Kinetic Parameters of Thiamine Diphosphate Binding to Transketolase

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R. V. Ospanov¹, G. A. Kochetov^2*, and B. I. Kurganov³

¹Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, 119992, Moscow, Russia; fax: (495) 939-3181; E-mail: ospanov@mail.genebee.msu.ru

²Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; fax: (495) 939-3181; E-mail: kochetov@mail.genebee.msu.ru

³Bach Institute of Biochemistry, Russian Academy of Sciences, Leninsky pr. 33, 119071 Moscow, Russia; fax: (495) 954-2732; E-mail: boris@kurganov.com

^* To whom correspondence should be addressed.

Received July 25, 2006; Revision received September 12, 2006

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The two-step mechanism of interaction of thiamine diphosphate (ThDP) with transketolase (TK) has been studied: TK + ThDP <--> TK···ThDP <--> TK*-ThDP. The scheme involves the formation of inactive intermediate complex TK···ThDP followed by its transformation into catalytically active holoenzyme, TK*-ThDP. The dissociation and kinetic constants for individual stages of this process have been determined. The values of forward and backward rate constants change in the presence of the donor substrate hydroxypyruvate. This finally leads to an increase in the overall affinity of the coenzyme to TK.

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KEY WORDS: transketolase, thiamine diphosphate, kinetic model

DOI: 10.1134/S0006297907010105

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