Inhibition of liver lysosomal acid phospholipase A1 by blood serum proteins.

Pathophysiological conditions may lead to a release of lysosomal acid phospholipase A1 like that of other lysosomal enzymes into the blood stream. As shown here, various serum protein fractions, obtained by dye-ligand affinity chromatography, inhibit phosphoglyceride hydrolysis by lysosomal acid phospholipase A1 in vitro. Their inhibitory potencies vary considerably, and the degree of inhibition depends on the substrate concentration. A delayed phospholipid flotation rate in sucrose gradients in the presence of one of the more potent inhibitory serum proteins, serum albumin, suggests that the inhibition is due to inhibitor-substrate interactions. Although lysosomal phospholipase A1 activity at blood pH is extremely low, serum proteins may contribute to protect biomembranes which are exposed to the vascular lumen against uncontrolled destruction by this enzyme.