Inorganic pyrophosphate metabolism in Saccharomyces cerevisiae

Inorganic pyrophosphate (PPi) in microorganisms has been shown to reach quite high levels, with profound implications for many aspects of cellular metabolism. It is shown that the level of PPi in the growing cells of Saccharomyces cerevisiae shows a remarkable variation along the growth curve, ranging from 2 to 35 mM. In contrast inorganic pyrophosphate (PPase) (for which PPi is a substrate) levels accompanying growth showed minimal variation. In seeking to understand the variation of PPi levels on the basis of yeast morphology and cell cycle, PPi levels were measured in: (1) cellular populations fractionated by Renografin density gradient separation; (2) cells grown synchronously following alpha factor arrest; and (3) cdc mutants grown at permissive and restrictive temperatures. The rise in PPi concentration was found to correlate with the fraction of small budded cells and coincided with the S phase of the cell cycle, during which DNA synthesis is occurring. Subcellular localization studies of PPi indicated that the vacuole is a major storage compartment, in which there was virtually no PPase present