Biosynthesis of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet activating factor and a hypotensive lipid) by cholinephosphotransferase in various rat tissues.
The unique alkyl phospholipid, 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine, has been reported to exhibit powerful antihypertensive activity (Blank, M.L., Snyder, F., Byers, L.W., Brooks, B. and Muirhead, E.E. (1979) Biochem. Biophys. Res. Commun. 90, 1194-1200) and appears to be an extremely potent platelet-activating factor (Demopoulos, C.A., Pinckard, R.N. and Hanahan, D.J. (1979) J. Biol. Chem. 254, 9355-9358). In the present study, microsomal preparations from several rat tissues were found to catalyze the synthesis of 1-alkyl-1-acetyl-sn-glycero-3-phosphocholine by 1-alkyl-2-acetyl-sn-glycerol:CDPcholine cholinephosphotransferase reaction. Optimal conditions to measure enzyme activity were established. A subcellular survey of this cholinephosphotransferase activity showed that the enzyme was of microsomal origin. Enzyme activity was found in microsomes from several tissues; however, spleen has the highest activity of the tissues examined. Three different species of 1-alkyl-2-acetyl-sn-glycerol were all found to be substrates. The 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine synthesized in the microsomes could be hydrolyzed by adding the 100,000 x g supernatant fraction to the incubation medium. The optimum pH for formation of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine was 8.0, which was different from the pH optimum of 8.5 observed for the long-chain diacylglycerol cholinephosphotransferases. Activity of cholinephosphotransferase towards 1-alkyl-2-acetyl-sn-glycerol was slightly enhanced and stabilized by dithiothreitol, whereas the activity towards a diacylglycerol was inhibited by dithiothreitol. The possible involvement of two different enzymes in the conversion of 1-alkyl-2-acetyl-sn-glycerol and diacylglycerol to their respective phospholipid products is discussed.
D000818:Animals; D000959:Antihypertensive Agents / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects; D003600:Cytosol / Q000378:metabolism; D002798:Diacylglycerol Cholinephosphotransferase / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism; D008244:Lysophosphatidylcholines / Q000096:biosynthesis*; D008297:Male; D008861:Microsomes / Q000201:enzymology; D008862:Microsomes, Liver / Q000201:enzymology*; D010770:Phosphotransferases / Q000378:metabolism*; D010972:Platelet Activating Factor; D051381:Rats; D013154:Spleen / Q000201:enzymology*; D013379:Substrate Specificity
D000959:Antihypertensive Agents; D004075:Diglycerides; D008244:Lysophosphatidylcholines; D010972:Platelet Activating Factor; D010770:Phosphotransferases; D002798:Diacylglycerol Cholinephosphotransferase