MAMMALIAN MG2-INDEPENDENT PHOSPHATIDATE PHOSPHATASE (PAP2) DISPLAYS DIACYLGLYCEROL PYROPHOSPHATE PHOSPHATASE-ACTIVITY()

Recent studies indicate that the metabolism of diacylglycerol pyrophos phate (DGPP) is involved in a novel lipid signaling pathway. DGPP phos phatases (DGPP phosphohydrolase) from Saccharomyces cerevisiae and Esc herichia coli catalyze the dephosphorylation of DGPP to yield phosphat idate (PA) and then catalyze the dephosphorylation of PA to yield diac ylglycerol. We demonstrated that the Mg2+-independent form of PA phosp hatase (PA phosphohydrolase, PAPS) purified from rat liver catalyzed t he dephosphorylation of DGPP. This reaction was Mg2+-independent, inse nsitive to inhibition by N-ethylmaleimide and bromoenol lactone, and i nhibited by Mn2+ ions. PAP2 exhibited a high affinity for DGPP (K-m = 0.04 mol %). The specificity constant (V-max/K-m) for DGPP was 1.3-fol d higher than that of Pk DGPP inhibited the ability of PAPS to dephosp horylate PA, and PA inhibited the dephosphorylation of DGPP. Like rat liver PAP2, the Mg2+-independent PA phosphatase activity of DGPP phosp hatase purified hom S. cerevisiae was inhibited by lyse-PA, sphingosin e l-phosphate, and ceramide l-phosphate. Mouse PAP2 showed homology to DGPP phosphatases from S. cerevisiae and E. coli, especially in local ized regions that constitute a novel phosphatase sequence motif. Colle ctively, our work indicated that rat liver PAP2 is a member of a phosp hatase family that includes DGPP phosphatases from S. cerevisiae and E . coli. We propose a model in which the phosphatase activities of rat liver PAP2 and the DGPP phosphatase of S. cerevisiae regulate the cell ular levels of DGPP, PA, and diacylglycerol.