Acid lipase and phospholipase activity in homogenates of rabbit polymorphonuclear leukocytes

In homogenates of rabbit polymorphonuclear leukocytes from peritoneal exudates, three different lipid splitting activities have been found by measuring the release of fatty acids using the following lipid substrates: 1) a commercial coconut oil suspension indicating lipase activity, 2) synthetic dipalmitoyllecithin or purified brain phospholipid demonstrating phospholipase activity, and 3) lysolecithin prepared from egg lecithin indicating lysophospholipase activity. Both lipase and phospholipase activity manifested a sharp pH optimum at pH 6.0. The lysophospholipase activity exhibited a distinctly alkaline pH optimum. Most activity was found in the 8,200 x g supernatant fraction of the homogenate, but considerable lipase and phospholipase activity was also associated with the granules of the leukocytes. However, little lysophospholipase activity was present in the granule fraction. Freezing and thawing increased lipase activity of the whole homogenate and the granules, but destroyed phospholipase activity. Since phagocytosis is accompanied by a fall in intracellular pH, the possibility exists that the lipid splitting activities with acid pH optima play a role in the events that occur during phagocytosis.