Isolation and Characterization of Polyphosphates from the Yeast Cell Surface

When cells of Saccharomyces fragilis are subjected to osmotic shock, they release a limited amount of inorganic polyphosphate into the medium, which represents about 10% of the total cellular content. The osmotic shock procedure causes no substantial membrane damage, as judged from the unimpaired cell viability, limited K+ leakage and low percentage of stained cells. It is therefore suggested that this polyphosphate fraction is localized outside the plasma membrane. The released polyphosphate fraction differs from the remaining cellular polyphosphates in two respects: the mean chain length of the shock-sensitive fraction is significantly higher than that of the total cellular polyphosphates and its metabolic turnover rate, subsequent to pulsing with [32P]orthophosphate is much lower compared to the rest of the cellular polyphosphate. Incubation of intact cells with the anion exchange resin Dowex AG 1-X4 results in the release of high molecular weight polyphosphates. These results suggest that the osmotic shock-sensitive polyphosphate fraction has specific characteristics in both its cellular localization and metabolism.