Relative suitability of 1-palmitoyl and 1-stearoyl homologues of 1-acyl-sn-glycerylphosphorylcholine and different acyl donors for phosphatidylcholine synthesis via acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase in rat lung microsomes.

The relative suitability of the 1-palmitoyl and 1-stearoyl homologues of 1-acyl-sn-glyceryl-phosphorylcholine and different acyl donors were tested as substrates for phosphatidylcholine synthesis via the acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase in rat lung microsomes. The acyl acceptor was an almost equi-molar mixture of the [3H]palmitoyl plus [14C]stearoyl species of 1-acyl-sn-glycero-3-phosphorylcholine with palmitoyl-, stearoyl-, oleoyl-, linoleoyl-, or arachidonoyl-CoA serving as the acyl donor. At all concentrations of acyl acceptor, reaction velocities with 20:4-CoA greater than or equal to 18:2-CoA > 18:1-CoA > 16:0-CoA >18:0-CoA. Furthermore, the acyltransferase selectively utilized the 1-palmitoyl over the 1-stearoyl species of 1-acylglycerylphosphorylcholine by 4.2- to 5.7-fold under optimal assay conditions with the various acyl-CoA thiolesters. However, the degree of preference exhibited for the 1-palmitoyl-sn-glycero-3-phosphorylcholine, as acyl acceptor, versus the 1-stearoyl homologue with palmitoyl-CoA as the acyl donor was not significantly different from that obtained with the other acyl-CoA derivatives. Thus, the specificity of the acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase indicates an ability of this enzyme to produce dipalmitoyl phosphatidylcholine but it cannot independently explain the predominance of dipalmitoyl phosphatidylcholine in lung or the tendency of stearate at the 1-position to associate with fatty acids of increasing unsaturation at the 2-position.