Purification and characterization of a soluble polyphosphatase from mitochondria of Saccharomyces cerevisiae

A polyphosphatase with the specific activity 2.2 U/mg was purified to apparent homogeneity from a soluble preparation of mitochondria of Saccharomyces cerevisiae. The polyphosphatase is a monomeric protein of approximately 41 kD. The purified enzyme hydrolyzes polyphosphates with an average chain length of 9 to 208 phosphate residues to the same extent, but its activity is approximately 2-fold higher with tripolyphosphate. ATP, PPi, and p-nitrophenyl phosphate are not substrates of this enzyme. The apparent Km values are 300, 18, and 0.25 microM obtained at hydrolysis of polyphosphates with a chain length of 3, 15, and 188 phosphate residues, respectively. Several divalent cations stimulated the enzyme activity 1.2-27-fold (Mg2+ = Co2+ = Mn2+ > Zn2+). Determination of the protein N-terminal sequence and its comparison with the EMBL data library indicates that the soluble polyphosphatase of mitochondria of S. cerevisiae is not encoded by the gene of the major yeast polyphosphatase PPX1.