Regulation of the DPP1-encoded Diacylglycerol Pyrophosphate (DGPP) Phosphatase by Inositol and Growth Phase INHIBITION OF DGPP PHOSPHATASE ACTIVITY BY CDP-DIACYLGLYCEROL AND ACTIVATION OF PHOSPHATIDYLSERINE SYNTHASE ACTIVITY BY DGPP*

The regulation of the Saccharomyces cerevisiae DPP1encoded diacylglycerol pyrophosphate (DGPP) phosphatase by inositol supplementation and growth phase was examined. Addition of inositol to the growth medium resulted in a dose-dependent increase in the level of DGPP phosphatase activity in both exponential and stationary phase cells. Activity was greater in stationary phase cells when compared with exponential phase cells, and the inositoland growth phase-dependent regulations of DGPP phosphatase were additive. Analyses of DGPP phosphatase mRNA and protein levels, and expression of b-galactosidase activity driven by a PDPP1lacZ reporter gene, indicated that a transcriptional mechanism was responsible for this regulation. Regulation of DGPP phosphatase by inositol and growth phase occurred in a manner that was opposite that of many phospholipid biosynthetic enzymes. Regulation of DGPP phosphatase expression by inositol supplementation, but not growth phase, was altered in opi1D, ino2D, and ino4D phospholipid synthesis regulatory mutants. CDP-diacylglycerol, a phospholipid pathway intermediate used for the synthesis of phosphatidylserine and phosphatidylinositol, inhibited DGPP phosphatase activity by a mixed mechanism that caused an increase in Km and a decrease in Vmax. DGPP stimulated the activity of pure phosphatidylserine synthase by a mechanism that increased the affinity of the enzyme for its substrate CDP-diacylglycerol. Phospholipid composition analysis of a dpp1D mutant showed that DGPP phosphatase played a role in the regulation of phospholipid metabolism by inositol, as well as regulating the cellular levels of phosphatidylinositol.