出版社：American Society for Biochemistry and Molecular Biology
摘要：We assessed the ability of endothelial lipase (EL) to hydrolyze the sn -1 and sn -2 fatty acids (FAs) from HDL phosphatidylcholine. For this purpose, reconstituted discoidal HDLs (rHDLs) that contained free cholesterol, apolipoprotein A-I, and either 1-palmitoyl-2-oleoylphosphatidylcholine, 1-palmitoyl-2-linoleoylphosphatidylcholine, or 1-palmitoyl-2-arachidonylphosphatidylcholine were incubated with EL- and control (LacZ)-conditioned media. Gas chromatography analysis of the reaction mixtures revealed that both the sn- 1 (16:0) and sn- 2 (18:1, 18:2, and 20:4) FAs were liberated by EL. The higher rate of sn- 1 FA cleavage compared with sn- 2 FA release generated corresponding sn- 2 acyl lyso-species as determined by MS analysis. EL failed to release sn- 2 FA from rHDLs containing 1- O -1′-hexadecenyl-2-arachidonoylphosphatidylcholine, whose sn- 1 position contained a nonhydrolyzable alkyl ether linkage. The lack of phospholipase A2 activity of EL and its ability to liberate [14C]FA from [14C]lysophosphatidylcholine (lyso-PC) led us to conclude that EL-mediated deacylation of phosphatidylcholine (PC) is initiated at the sn- 1 position, followed by the release of the remaining FA from the lyso-PC intermediate. Thin-layer chromatography analysis of cellular lipids obtained from EL-overexpressing cells revealed a pronounced accumulation of [14C]phospholipid and [14C]triglyceride upon incubation with 1-palmitoyl-2-[1-14C]linoleoyl-PC-labeled HDL3, indicating the ability of EL to supply cells with unsaturated FAs.
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