Hydrolysis of Tripolyphosphate by Purified Exopolyphosphatase from Saccharomyces cerevisiae Cytosol: Kinetic Model

T. V. Kulakovskaya^*, N. A. Andreeva, A. V. Karpov, I. A. Sidorov, and I. S. Kulaev

Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (7-095) 923-3602; E-mail: alla@ibpm.serpukhov.su

^* To whom correspondence should be addressed.

Received November 16, 1998; Revision received April 6, 1999

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The kinetics of hydrolysis of tripolyphosphate by purified exopolyphosphatase from Saccharomyces cerevisiae cytosol has been studied in the presence of Mg²⁺. Two kinetic models suggesting the formation of complexes of tripolyphosphate and the enzyme with Mg²⁺ are compared. Both models suggest that only enzyme--substrate complexes containing Mg²⁺ and tripolyphosphate simultaneously are able to hydrolyze the tripolyphosphate. The first model suggests that the enzyme is able to bind to Mg²⁺ independently from substrate binding. The second model does not consider this possibility, but suggests that both complexes containing tripolyphosphate and Mg²⁺ in proportion 1:1 and 1:2 can serve as the reaction substrates. The description of the experimental data by both models is essentially the same. The complex containing tripolyphosphate and Mg²⁺ in proportion 1:1 is optimal for the enzyme activity, the complex containing tripolyphosphate and Mg²⁺ in proportion 1:2 being hydrolyzed at a lower rate.

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KEY WORDS: exopolyphosphatase, tripolyphosphate, Mg²⁺, cytosol, yeast, Saccharomyces cerevisiae, kinetic model

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