Regulation of the DPP1-encoded diacylglycerol pyrophosphate (DGPP) phosphatase by inositol and growth phase - Inhibition of DGPP phosphatase activityby CDP-diacylglycerol and activation of phosphatidylserine synthase activity by DGPP

The regulation of the Saccharomyces cerevisiae DPP1-encoded diacylglycerol pyrophosphate (DGPP) phosphatase by inositol supplementation and growth pha se was examined. Addition of inositol to the growth medium resulted in a do se-dependent increase in the level of DGPP phosphatase activity in both exp onential and stationary phase cells. Activity was greater in stationary pha se cells when compared with exponential phase cells, and the inositol- and growth phase-dependent regulations of DGPP phosphatase were additive. Analy ses of DG;PP phosphatase mRNA and protein levels, and expression of beta -g alactosidase activity driven by a P-DPP1-lacZ reporter gene, indicated that a transcriptional mechanism was responsible for this regulation. Regulatio n of DGPP phosphatase by inositol and growth phase occurred in a manner tha t was opposite that of many phospholipid biosynthetic enzymes. Regulation o f DGPP phosphatase expression by inositol supplementation, but not growth p hase, was altered in opi1 Delta, ino2 Delta, and ino4 Delta phospholipid sy nthesis regulatory mutants. CDP-diacylglycerol, a phospholipid pathway inte rmediate used for the synthesis of phosphatidylserine and phosphatidylinosi tol, inhibited DGPP phosphatase activity by a mixed mechanism that caused a n increase in K-m and a decrease in V-max. DGPP stimulated the activity of pure phosphatidylserine synthase by a mechanism that increased the affinity of the enzyme for its substrate CDP-diacylglycerol, Phospholipid compositi on analysis of a dpp1 Delta mutant showed that DGPP phosphatase played a ro le in the regulation of phospholipid metabolism by inositol, as well as reg ulating the cellular levels of phosphatidylinositol.