title: Kinetic and topographical studies of the phosphatidylcholine: ceramide choline phosphotransferase in plasma membrane particles from mouse ascites cells.
abstract: The content of endogenous phospholipids in plasma membrane preparations from Ehrlich ascites cells was depleted by exposure to phospholipase C. The enzyme catalyzing the phosphatidylcholine: ceramide choline phosphotransferase reaction was inactivated by this treatment. However, the activity could be restored with exogenous phosphatidylcholines, demonstrating the dependence of the reaction upon the presence of this substrate. Phosphatidylcholines containing unsaturated fatty acids were 10-fold more effective substrates than the saturated molecular species. The activation energy of the reaction was determined to be 17.2 kcal/mol. Selective trypsin treatment of the plasma membranes suggests that the cholinephosphotransferase may have an asymmetric orientation. The reaction kinetics followed a rate equation similar to that of the ping-pong reaction mechanism, which suggests the formation of an enzyme-bound intermediate of the phosphocholine group being transferred. These results are discussed in terms of possible biological functions of the enzyme.
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000201:enzymology*; D002462:Cell Membrane / Q000032:analysis / Q000187:drug effects; D004075:Diglycerides / Q000494:pharmacology; D007700:Kinetics; D008081:Liposomes; D008563:Membrane Lipids / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000378:metabolism*; D010739:Phospholipase D / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism; D010770:Phosphotransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013109:Sphingomyelins / Q000096:biosynthesis; D013379:Substrate Specificity; D013696:Temperature; D017855:Transferases (Other Substituted Phosphate Groups); D014357:Trypsin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000494:pharmacology
chemical_list: D004075:Diglycerides; D008081:Liposomes; D008563:Membrane Lipids; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D010743:Phospholipids; D013109:Sphingomyelins; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); C019863:ceramide cholinephosphotransferase; D010738:Type C Phospholipases; D010739:Phospholipase D; D014357:Trypsin