Endopolyphosphatases for long chain inorganic polyphosphate in yeast and mammals

Whereas exopolyphosphatases have been purified from yeast and a variety of bacteria, this is the first report characterizing endopolyphosphatases that act on long chain inorganic polyphosphate (polyP). The activity from Saccharomyces cerevisiae, localized in vacuoles, has been purified to homogeneity from a strain that possesses vacuolar proteases. The endopolyphosphatase is a dimer of 35-kDa subunits. Distributive action on polyP750 produces shorter chains to a limit of about polyP60, as well as the more abundant release of polyP3; the Km for polyP750 is 185 nM. Endopolyphosphatases have been identified in a wide variety of sources, except for most eubacteria tested. The activity has been partially purified from rat and bovine brain where its abundance is about 10 times higher than in other tissues but less than 1/10 that of yeast; the limit product of digestion of the partially purified brain enzyme is polyP3.