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 appar ent homogeneity from a soluble preparation of mitochondria of Saccharomyces cerevisiae. The polyphosphatase is a monomeric protein of similar to 41 kD . The purified enzyme hydrolyzes polyphosphates with an average chain lengt h of 9 to 208 phosphate residues to the same extent, but its activity is si milar to 2-fold higher with tripolyphosphate. ATP, PPi, and p-nitrophenyl p hosphate are not substrates of this enzyme. The apparent K-m values are 300 , 18, and 0.25 mu M obtained at hydrolysis of polyphosphates with a chain l ength of 3, 15, and 188 phosphate residues, respectively. Several divalent cations stimulated the enzyme activity 1.2-27-fold (Mg2+ = Co2+ = Mn2+ > Zn 2+). Determination of the protein N-terminal sequence and its comparison wi th the EMBL data library indicates that the soluble polyphosphatase of mito chondria of S, cerevisiae is not encoded by the gene of the major yeast pol yphosphatase PPX1.