title: Conversion of 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine to 1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine. A novel pathway for the metabolism of ether-linked phosphoglycerides.
abstract: Madin Darby canine kidney (MDCK) cells convert 1-O-[3H]alkyl-2-acyl-sn-glycero-3-phosphocholine [( 3H]alkylacylGPC) to a product tentatively identified as an ethanolamine-containing phosphoglyceride (PE) (Daniel, L. W., Waite, B. M., and Wykle, R. L. (1986) J. Biol. Chem. 261, 9128-9132). In the present study, analysis of the radiolabeled phosphoglycerides as diradylglycerobenzoate derivatives indicated that [3H] alkylacylGPC was initially converted to 1-O-[3H]alkyl-2-acyl-sn-glycero-3-phosphoethanolamine [( 3H]alkylacylGPE) which was subsequently desaturated to 1-O-[3H]alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine [( 3H]alkenylacylGPE). The conversion of [3H]/[32P]alkyl-lysoGPC to [3H]alkenylacylGPE indicated that base exchange enzymes were not involved in this pathway. A phosphono analog of alkyl-lysoGPC, resistant to phospholipase D hydrolysis and radiolabeled in the 1-O-alkyl chain was readily incorporated, acylated, and subsequently metabolized to [3H]alkylacylGPC and [3H]alkenylacylGPE. Therefore, the involvement of phospholipase D in the conversion pathway was ruled out. The conversion of [3H]alkylacylGPC or its phosphono analog to [3H]alkenylacylGPE was significantly enhanced by the addition of 100 microM ethanolamine to the culture media, suggesting that [3H]alkylacylglycerol is an intermediate in the cytidine-dependent pathway of PE synthesis. MDCK cell cytosol and microsomes contained no detectable phospholipase C activity. However, incubation of microsomes with CMP resulted in the degradation of [3H]alkylacylGPC and accumulation of [3H]alkylacylglycerol. Furthermore, the addition of CDP-ethanolamine to microsomes following preincubation with CMP, resulted in a decrease in [3H]alkylacylglycerol with a concomitant increase in [3H]alkenylacylGPE. Overall, these results suggest that the reverse reaction of choline phosphotransferase may be responsible for the conversion of alkylacylGPC to alkylacylGPE.
authors.affiliation: Department of Biochemistry, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1016.
authors.forename: J C
authors.initials: JC
authors.lastname: Strum
authors.forename: A
authors.initials: A
authors.lastname: Emilsson
authors.forename: R L
authors.initials: RL
authors.lastname: Wykle
authors.forename: L W
authors.initials: LW
authors.lastname: Daniel
mesh_terms: D000818:Animals; D002460:Cell Line; D003600:Cytosol / Q000201:enzymology; D002798:Diacylglycerol Cholinephosphotransferase / Q000378:metabolism; D004285:Dogs; D004987:Ethers / Q000378:metabolism; D007202:Indicators and Reagents; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D010713:Phosphatidylcholines / Q000378:metabolism*; D010714:Phosphatidylethanolamines / Q000302:isolation & purification / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D014316:Tritium
chemical_list: D004987:Ethers; D007202:Indicators and Reagents; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010761:Phosphorus Radioisotopes; D014316:Tritium; D002798:Diacylglycerol Cholinephosphotransferase; D010740:Phospholipases