Evidence that hydrolysis of ethanolamine plasmalogens triggers synthesis of platelet-activating factor via a transacylation reaction.
Addition of 1-O-alk-1'-enyl-2-lyso-sn-glycero-3-phosphoethanolamine (alkenyl-lyso-GPE) to human neutrophil membrane preparations containing 1-O-[3H]hexadecyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (1-O-[3H]alkyl-2-arachidonoyl-GPC) resulted in rapid deacylation of the 1-O-[3H]alkyl-2-arachidonoyl-GPC to 1-O-[3H]alkyl-2-lyso-GPC (lyso-platelet-activating factor, lyso-PAF). When acetyl-CoA was included in the incubation mixture, the [3H]lyso-PAF was converted to [3H]PAF. Studies of [3H]arachidonate-labeled neutrophils permeabilized with Staphlococcus aureus alpha-toxin revealed a major shift of labeled [3H]arachidonate from the choline to the ethanolamine-containing phosphoglycerides upon addition of alkenyl-lyso-GPE. The studies indicated that lyso-PAF is formed in the system by the transfer of arachidonate from 1-O-alkyl-2-arachidonoyl-GPC to the alkenyl-lyso-GPE by a CoA-independent transacylase reaction. Mass measurements revealed a rapid loss of arachidonate from 1-radyl-2-acyl-GPE and a concomitant increase in alkenyl-lyso-GPE upon stimulation of the neutrophils by ionophore A23187. Based on these and other findings, a pathway is proposed that may play a significant, if not obligatory, role in the synthesis of PAF in intact stimulated neutrophils. It has been widely accepted that phospholipase A2 acts directly on 1-O-alkyl-2-arachidonoyl-GPC as the first step in the synthesis of PAF via formation of lyso-PAF. In the proposed scheme, phospholipase A2, upon stimulation, acts rapidly on ethanolamine plasmalogen selectively releasing arachidonic acid and generating alkenyl-lyso-GPE. The CoA-independent transacylase then selectively transfers arachidonate from 1-radyl-2-arachidonoyl-GPC to the alkenyl-lyso-GPE generating lyso-PAF, which is then acetylated to form PAF. The interactions outlined can account for the synthesis of 1-acyl-2-acetyl-GPC, 1-O-alk-1'-enyl-2-acetyl-GPE, and eicosanoids, in parallel with PAF.
Department of Biochemistry, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27103.
M L
ML
Nieto
M E
ME
Venable
S A
SA
Bauldry
D G
DG
Greene
M
M
Kennedy
D A
DA
Bass
R L
RL
Wykle
D000215:Acylation; D000217:Acyltransferases / Q000378:metabolism; D001095:Arachidonic Acids / Q000378:metabolism; D002474:Cell-Free System; D004983:Ethanolamines / Q000378:metabolism*; D005997:Glycerylphosphorylcholine / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D009504:Neutrophils / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D010955:Plasmalogens / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000096:biosynthesis*; D013379:Substrate Specificity
D001095:Arachidonic Acids; D004983:Ethanolamines; D010743:Phospholipids; D010955:Plasmalogens; D010972:Platelet Activating Factor; D005997:Glycerylphosphorylcholine; D000217:Acyltransferases