ENDOPOLYPHOSPHATASES FOR LONG-CHAIN INORGANIC POLYPHOSPHATE IN YEAST AND MAMMALS

Whereas exopolyphosphatases have been purified from yeast and a variet y of bacteria, this is the first report characterizing endopolyphospha tases that act on long chain inorganic polyphosphate (polyP). The acti vity from Saccharomyces cerevisiae, localized in vacuoles, has been pu rified to homogeneity from a strain that possesses vacuolar proteases. The endopolyphosphatase is a dimer of 35-kDa subunits. Distributive a ction on polyP(750) produces shorter chains to a limit of about polyP( 60), as well as the more abundant release of polyP(3); the K-m for pol yP(750) is 185 nM. Endopolyphosphatases have been identified in a wide variety of sources, except for most eubacteria tested. The activity h as been partially purified from rat and bovine brain where its abundan ce is about 10 times higher than in other tissues but less than 1/10 t hat of yeast; the limit product of digestion of the partially purified brain enzyme is polyP(3).