Partial Purification and Characterization of Nuclear Exopolyphosphatase from Saccharomyces cerevisiae Strain with Inactivated PPX1 Gene Encoding a Major Yeast Exopolyphosphatase

L. P. Lichko^*, T. V. Kulakovskaya, and I. S. Kulaev

Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino 142290, Moscow Region, Russia; fax: (7-095) 923-3602; E-mail: alla@ibpm.pushchino.ru

^* To whom correspondence should be addressed.

Received May 14, 2003; Revision received July 9, 2003

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Inactivation of PPX1 encoding the major cytosolic exopolyphosphatase PPX1 in Saccharomyces cerevisiae did not alter exopolyphosphatase activity of the isolated nuclei compared with that in the parent strain. The nuclear exopolyphosphatase of the S. cerevisiae strain deficient in the PPX1 gene was purified 10-fold. According to gel filtration on Superose 6, this enzyme has a molecular mass of ~200 kD, and it hydrolyzes polyphosphates with an average chain length of 15 and 208 phosphate residues to the same extent. Its activity is much lower with tripolyphosphate. In the presence of 2.5 mM Mg²⁺, K_m values are 133 and 25 µM in the hydrolysis of polyphosphates with chain lengths of 15 and 208 phosphate residues, respectively. The enzyme activity is stimulated by 2.5 mM Mg²⁺ and 0.1 mM Co²⁺ 15- and 31-fold, respectively. RNA does not alter the nuclear exopolyphosphatase activity, while polylysine increases it 2-fold.

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KEY WORDS: exopolyphosphatase, polyphosphate, nuclei, PPX1-deficient strain, Saccharomyces cerevisiae

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