Positional specificity of lysosomal phospholipase A2

Akira Abe, Miki Hiraoka, and James A. Shayman

Internal Medicine, University of Michigan, Ann Arbor, MI 48109-0676

Corresponding Author: jshayman{at}umich.edu

Lysosomal phospholipase A2 (Lpla2) is highly expressed in alveolar macrophages and may mediate the phospholipid metabolism of surfactant. Studies on the properties of this phospholipase are consistent with the presence of both phospholipase A1 and phospholipase A2 activities. These activities were studied through the production of O-acyl-compounds, produced by the transacylase activity of Lpla2. Liposomes containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and N-acetylsphingosine (NAS) were incubated with the soluble fraction obtained from MDCK cells stably transfected with the mouse Lpla2 gene. Two 1-O-acyl-NASs, 1-O-palmitoyl-NAS and 1-O-oleoyl-NAS, were produced by Lpla2. The formation of 1-O-oleoyl-NAS was 2.5 fold that of 1-O-palmitoyl-NAS. When 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) was used, the formation of 1-O-oleoyl-NAS was five-fold higher than that of 1-O-palmitoyl-NAS. Thus Lpla2 can act on acyl groups at both sn-1 and sn-2 positions of POPC and OPPC. When 1-palmitoyl-2-unsaturated acyl-sn-glycero-3-phosphocholines were used as acyl donors, the transacylation of the acyl group from the sn-2 position to NAS was preferred to that of the palmitoyl group from the sn-1 position. An exception was observed for 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC) where the formation of 1-O-palmitoyl-NAS from PAPC was 4-fold greater than that of 1-O-arachidonoyl-NAS. Thus Lpla2 has broad positional specificity for the sn-1 and sn-2 acyl groups in phosphatidylcholine and phosphatidylethanolamine.

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