title: Studies of diacylglycerol cholinephosphotransferase and diacylglycerol ethanolaminephosphotransferase activities in Tetrahymena microsomes.
abstract: Microsomes isolated from Tetrahymena pyriformis synthesized phosphatidylcholine and phosphatidylethanolamine by CDPcholine: 1,2-diacylglycerol cholinephosphotransferase (EC 2.7.8.2) and CDPethanolamine: 1,2-diacylglycerol ethanolaminephosphotransferase (EC 2.7.8.1), utilizing ethanol-dispersed dioleoglycerol. Cholinephosphotransferase and ethanolaminephosphotransferase activities have similar dependences on MgCl2 and MnCl2, but the latter was more effective than the former for both enzyme activities. The V values for 1,2-dioleoylglycerol obtained at optimal conditions were 1.8 nmol/min per mg microsomal protein for cholinephosphotransferase and 0.6 nmol/min per mg microsomal protein for ethanolaminephosphotransferase. Both enzymes could not utilize 1,3-dioleoylglycerol or 1-oleoylglycerol as substrates. Cholinephosphotransferase had an apparent Km for CDPcholine of 11.7 microM with 1,2-dioleoylglycerol and was inhibited by CDPethanolamine competitively. On the other hand, ethanolaminephosphotransferase has an apparent Km for CDPethanolamine of 8 microM and CDPcholine was a noncompetitive inhibitor of ethanolaminephosphotransferase activity. Furthermore, despite the marked alteration of phospholipid composition occurring during the temperature acclimation of Tetrahymena cells, both enzyme activities showed similar dependences on growth and incubation temperatures. This may imply that the final step of de novo synthesis of two major phospholipids does not participate in the thermally induced modification of the profile of phospholipid polar head group in membranes.
mesh_terms: D000818:Animals; D002798:Diacylglycerol Cholinephosphotransferase / Q000378:metabolism*; D004982:Ethanolaminephosphotransferase / Q000378:metabolism*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology*; D010770:Phosphotransferases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology; D013379:Substrate Specificity; D013696:Temperature; D013769:Tetrahymena pyriformis / Q000201:enzymology* / Q000254:growth & development; D013816:Thermodynamics
chemical_list: D010770:Phosphotransferases; D004982:Ethanolaminephosphotransferase; D002798:Diacylglycerol Cholinephosphotransferase