Polyphosphatase PPN1 of Saccharomyces cerevisiae Is a Deoxyadenosine Triphosphate Phosphohydrolase

The Saccharomyces cerevisiae polyphosphatase PPN1 (uniprot/Q04119) degrades inorganic polyphosphates both by cleaving Pi from the chain end and by fragmenting long-chain polymers into shorter ones. In this study, we have found a new activity of this protein: it releases phosphate from dATP. The dATP phosphohydrolase activity of pure PPN1 was ~7-fold lower compared to the exopolyphosphatase activity. This activity was strongly stimulated by Co2+ ions, as well as by ammonium ions, and inhibited by heparin and pyrophosphate similar to the exopolyphosphatase activity of PPN1. The Km value for dATP was 0.88 ± 0.14 mM. The dATP phosphohydrolase activity in the cells of PPN1-overexpressing yeast strain was several-fold higher than that in the parent strain. The other exopolyphosphatase of S. cerevisiae, PPX1, did not split Pi from dATP.