NMR-Observed Phosphate Trafficking and Polyphosphate Dynamics in Wild-Type and vphl-l Mutant Saccharomyces cerevisae in Response to Stresses

The phosphagenic, osmotic, and metabolic roles of polyphosphate in chemostatcultivated yeast were investigated with a new NMR cultivator. Wild-type yeast and a vacuolar vph1-1 mutant, which lacks polyphosphate, were subjected to different stimuli. Starved wild-type yeast exclusively directed phosphate to vacuoles despite other competing sinks. After DNP or iodoacetate exposure, which significantly affected cytosolic pH or ATP metabolism, polyphosphate hydrolysis did not occur, which casts doubt on the phosphagen function of vacuolar polyphosphate. It took about 1 h for Mn^2+ to traffic to vacuoles, and some evidence was obtained for polyphosphate responding to osmotic challenges. Fast NMR scans show that rapid polyphosphate hydrolysis to small polymers follows alkalinization. The small polymers then degrade to orthophosphate, which coincides with sugar phosphates increasing and subsequent reacidification. In contrast, when vph1-1 mutants were subjected to alkalinization, the absence of a vacuolar source of phosphate slowed reacidification. Based on known yeast physiology and observed sugar phosphate dynamics, polyphosphate degradation may enable rapid glycogen mobilization to glycolysis for considerable acid and ATP production. Overall, maintaining both polyphosphate and carbohydrate reserves may endow yeast with the ability to rapidly manage the extracellular environment.