NMR-observed phosphate trafficking and polyphosphate dynamics in wild-typeand vph1-1 mutant Saccharomyces cerevisiae in response to stresses

The phosphagenic, osmotic, and metabolic roles of polyphosphate in chemosta t-cultivated yeast were investigated with a new NMR cultivator. Wild-type y east and a vacuolar vph1-1 mutant, which lacks polyphosphate, were subjecte d to different stimuli. Starved wild-type yeast exclusively directed phosph ate to vacuoles despite other competing sinks. After DNP or iodoacetate exp osure, which significantly affected cytosolic pH or ATP metabolism, polypho sphate hydrolysis did not occur, which casts doubt on the phosphagen functi on of vacuolar polyphosphate. It took about 1 h for Mn2+ to traffic to vacu oles, and some evidence was obtained for polyphosphate responding to osmoti c challenges. Fast NMR scans show that rapid polyphosphate hydrolysis to sm all polymers follows alkalinization. The small polymers then degrade to ort hophosphate, which coincides with sugar phosphates increasing and subsequen t reacidification. In contrast, when vph1-1 mutants were subjected to alkal inization, the absence of a vacuolar source of phosphate slowed reacidifica tion. Based on known yeast physiology and observed sugar phosphate dynamics , polyphosphate degradation may enable rapid glycogen mobilization to glyco lysis for considerable acid and ATP production. Overall, maintaining both p olyphosphate and carbohydrate reserves may endow yeast with the ability to rapidly manage the extracellular environment.