Phosphatidate phosphohydrolase catalyzes the hydrolysis of ceramide 1- phosphate, lysophosphatidate, and sphingosine 1-phosphate

A Mg2+-independent phosphatidate phosphohydrolase was purified from rat liver plasma membranes in two distinct forms, an anionic protein and a cationic protein. Both forms of the enzyme dephosphorylated phosphatidate, ceramide 1-phosphate, lysophosphatidate, and sphingosine 1-phosphate. When assayed at a constant molar ratio of lipid to Triton X-100 of 1:500, the apparent K(m) values of the anionic phosphohydrolase for the lipid substrates was 3.5, 1.9, 0.4, and 4.0 μM, respectively. The relative catalytic efficiency of the enzyme for phosphatidate, ceramide 1-phosphate, lysophosphatidate, and sphingosine 1-phosphate was 0.16, 0.14, 0.48, and 0.04 liter (min · mg)-1, respectively. The hydrolysis of phosphatidate was inhibited competitively by ceramide 1-phosphate, lysophosphatidate, and sphingosine 1-phosphate. The K((i)(app)) values were 5.5, 5.9, and 4.0 μM, respectively. The hydrolysis of phosphatidate by the phosphohydrolase conformed to a surface dilution kinetic model. It is concluded that the enzyme is a lipid phosphomonoesterase that could modify the balance of phosphatidate, ceramide 1-phosphate, lysophosphatidate, and sphingosine 1- phosphate relative to diacylglycerol, ceramide, monoacylglycerol, and sphingosine, respectively. The enzyme could thus play an important role in regulating cell activation and signal transduction.This work was supported in part by Grant MT 10504 from the Canadian Medical Research Council.Peer Reviewe