Deacylation of Dipalmitoyllecithin by Phospholipases a in Alveolar Macrophages

Abstract

Optimal conditions in vitro were established for the assay of phospholipases A of Bacillus Calmette Guerin-induced alveolar macrophages that deacylated dipalmitoyllecithin in the alkaline pH range. Sodium deoxycholate and Ca⁺⁺ were found to stimulate both phospholipases A₁ and A₂, whereas sodium dodecylsulfate strongly inhibited both enzyme activities. Other detergents like Triton X-100, Triton WR-1339, and Tween-20 activated phospholipase A₁, whereas they had no effect on or slightly inhibited the phospholipase A₂ enzyme. These phospholipases preferentially removed palmitic acid regardless of the position of palmitic acid on the phospholipid molecule and were more active on phosphatidylcholines than phosphatidylethanolamines. This suggests a role for macrophage phospholipases A in the clearance of saturated lecithins in the pulmonary surfactant complex.