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Phosphatidate phosphatase is a key regulatory enzyme in lipid metabolism, catalyzing the conversion of phosphatidate to diacylglycerol. The two substrates of PAP are phosphatidate and H2O, and its two products are diacylglycerol and phosphate, as shown here.
The reverse reaction is catalyzed by the enzyme diacylglycerol kinase , which replaces the hydroxyl group on diacylgylcerol with a phosphate from ATP, generating ADP in the process. While ATP is used by DGK in mammalian cells, yeast cells tend to use CTP as the high-energy phosphate donor instead. Mechanistically speaking, this has no effect on the overall reaction.
In yeast, the forward direction is Mg 2 + {\displaystyle {\ce {Mg^2+}}} -dependent, while the reverse direction is Ca 2 + {\displaystyle {\ce {Ca^2+}}} -dependent. PAP1, a cytosolic phosphatidate phosphatase found in the lung, is also Mg 2 + {\displaystyle {\ce {Mg^2+}}} -dependent, but PAP2, a six-transmembrane-domain integral protein found in the plasma membrane, is not.