Phospholipase A and acid lipase activity during release of lysosomal hydrolases.

Hydrolysis of cardiac and hepatic lysosomal phospholipids by endogenous phospholipase A occurs during incubation at 37 degrees C at pH 5.0. Lysophospholipids and free fatty acids accumulate in association with release of hydrolases from the lysosomes into the supernatant. Acid-active neutral lipid lipases contribute to the release of free fatty acids. Albumin inhibits the production of these surface-active lipids as well as the release of hydrolases. The soluble phospholipase A is inhibited by albumin, soluble protein (cytoplasmic), heparin, and protamine sulfate. Thus, hydrolysis of lysosomal lipids, catalyzed by endogenous phospholipases, as well as acid-active neutral lipid lipases, may contribute significantly to the increased permeability, swelling, and subsequent lysis of lysosomes. Stabilization of the lysosomal membrane is associated with integrity of the structural lipids of the membrane.