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

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+, Km 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.