31P NMR studies of intracellular pH and phosphate metabolism during cell division cycle of Saccharomyces cerevisiae.

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Abstract
Changes in intracellular pH and phosphate metabolism during the cell cycle of S. cerevisiae (NCYC 239) were analyzed by using high-resolution 31P NMR spectroscopy. High-density yeast cultures (2 .times. 108 cells/ml) were arrested prior to start by sequential glucose deprivation, after which they synchronously replicated DNA and divided after a final glucose feeding. Oxygenation of arrested cultures in the absence of glucose led to increased levels of sugar phosphates and ATP and an increase in intracellular pH. These conditions did not initiate cell cycle progression indicating that energization is not used as an intracelllular signal for initiation of the cell division cycle and that the cells need exogenous C sources for growth. Glucose refeeding initiated an alkaline intracellular pH transient only in the synchronous cultures; increased intracellular pH accompanies the traversal of start. Changes in phosphate flow and utilization were observed in the synchronous cultures. There was increased consumption of external phosphate during DNA synthesis. When external phosphate levels were low, the cells consumed their internal polyphosphate stores. Under these conditions polyphosphate apparently acts as a phosphate supply.