Comparison of acceptor and donor substrates in the CoA-independent transacylase reaction in human neutrophils.
In human neutrophils (PMN) the ethanolamine-containing phosphoglyceride fraction (PE), principally plasmalogen-linked PE (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine), is the major store of arachidonic acid (AA). Exogenous AA is initially incorporated into 1-acyl-linked phosphoglycerides and is believed to be transferred into the 1-ether-linked phosphoglycerides via the action of a CoA-independent transacylase (CoA-IT). We have investigated the selectivity for both the "acceptor' lysophospholipids and "donor' AA-containing phospholipid substrates in the CoA-IT reaction. Evidence suggests CoA-IT may also participate in the synthesis of platelet activating factor. The transfer of [3H]AA from endogenously labeled choline-containing phosphoglycerides (PC) to exogenously added alkenyl-lyso-PE (0-50 microM) was examined in saponin-permeabilized PMN. In these "donor' studies, we observed that [3H]AA was transferred from both alkyl- and diacyl-linked PC in a proportional manner. More detailed molecular species analysis showed that [3H]AA was deacylated from all the major AA-containing molecular species in both the alkyl and diacyl subclasses with no selectivity for either subclass. To investigate the "acceptor' selectivity, membrane fractions prelabeled with either [3H]alkyl-arachidonoyl-PE or -PC were utilized as donor substrates. Various unlabeled lysophospholipids (10 microM) were added and the generation of [3H]lyso-PE or -PC was monitored as a measure of CoA-IT activity. Significant subclass preference was observed upon addition of lyso-PE species (1-alkenyl > 1-alkyl > 1-acyl) however, little selectivity was seen with the corresponding lyso-PC species. On the other hand, lysophosphatidylserine, lysophosphatidylinositol, and lysophosphatidic acid all served as poor acceptor substrates in the reaction. These data from PMN are consistent with other evidence that the CoA-IT plays a pivotal role in the enrichment of AA into plasmalogen-linked PE.
Nixon
A B
AB
Department of Biochemistry, Bowman Gray School of Medicine, Winston-Salem, NC 27157-1016, USA.
Greene
D G
DG
Wykle
R L
RL
D000215:Acylation; D000217:Acyltransferases / Q000378:metabolism*; D016718:Arachidonic Acid / Q000378:metabolism*; D002463:Cell Membrane Permeability; D005994:Glycerophosphates / Q000378:metabolism*; D006801:Humans; D008246:Lysophospholipids / Q000378:metabolism*; D008563:Membrane Lipids / Q000378:metabolism; D009504:Neutrophils / Q000201:enzymology*; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010972:Platelet Activating Factor / Q000378:metabolism; D013379:Substrate Specificity
D005994:Glycerophosphates; D008246:Lysophospholipids; D008563:Membrane Lipids; D010714:Phosphatidylethanolamines; D010972:Platelet Activating Factor; C002449:glycerophosphoethanolamine; D016718:Arachidonic Acid; D000217:Acyltransferases; C039766:arachidonyl transacylase