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 Km values of the anionic phosphohydrolase for the lipid substrates was 3.5, 1.9, 0.4, and 4.0 microM, 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 x mg)-1, respectively. The hydrolysis of phosphatidate was inhibited competitively by ceramide 1-phosphate, lysophosphatidate, and sphingosine 1-phosphate. The Ki(app) values were 5.5, 5.9, and 4.0 microM, 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.
Waggoner
D W
DW
Signal Transduction Laboratories, Lipid and Lipoprotein Research Group, University of Alberta, 357 Heritage Medical Research Centre, Edmonton, Alberta T6G 2S2, Canada.
Gómez-Muñoz
A
A
Dewald
J
J
Brindley
D N
DN
D000818:Animals; D002384:Catalysis; D002518:Ceramides / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008246:Lysophospholipids / Q000378:metabolism*; D010711:Phosphatidate Phosphatase / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D015290:Second Messenger Systems; D015398:Signal Transduction; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism; D013379:Substrate Specificity
D002518:Ceramides; D008246:Lysophospholipids; C065576:ceramide 1-phosphate; C060506:sphingosine 1-phosphate; D010711:Phosphatidate Phosphatase; D013110:Sphingosine; D005033:Ethylmaleimide