Acylchain Specificity and Kinetic Properties of Phospholipase Ax and A2 of Bone Marrow-Derived Macrophages

Phospholipase A 1/A2, Macrophages, Arachidonic Acid, Acylchain Specificity The fatty acyl specificity of phospholipase A[ and A2 in homogenates of mouse bone marrowderived macrophages was determined using phosphatidylcholine and phosphatidylethanolamine of different acylchain composition. Phosphatidylcholine with arachidonoyl at position 2 was cleaved preferentially by an alkaline phospholipase A2 (pH-optimum 9.0) leading to selective liberation of arachidonic acid. In contrast, phosphatidylcholines with oleoyl or linoleoyl at posi­ tion 2 were degraded mainly by an acid phospholipase A! (pH-optimum 4 -5 ) resulting in a conservation of these fatty acids esterified in lysophosphatides. Substrate kinetics of the alkaline phospholipase A2 revealed a 30 fold higher affinity (Km = 3.8 x 10"7 m ) for l-acyl-2-arachidonoylglycerophosphocholine compared to l-acyl-2-oleoyl-glycerophosphocholine. The kinetic data were not influenced by endogenous lipids indicating that exogenous substrates do not equilibrate with cellular lipids. These results are suitable to explain a selective liberation of arachidonic acid from a mixture of phospholipids.