Inhibition of cytolysin activity in large granular lymphocyte granules by lipids: Evidence for a membrane insertion mechanism of lysis

Abstract

The ability of various compounds to inhibit the lytic activity of purified cytoplasmic granules from LGL tumors was tested. The lytic activity of granule cytolysin was modestly inhibited by inorganic phosphate, and various monophosphoesters, with I 50 values in the range of 8–20 m M. Among monophosphoesters, choline phosphate was exceptionally potent, with an I 50 of 1.4m M. In contrast to the inhibition by phosphate esters, the parent compounds such as neutral sugars, glycerol, and choline, showed no detectable inhibition at 50 m M. A lysolipid bearing a short aliphatic chain and some detergents were inhibitory with I 50 values in the range of 1 m M. Lysolipids with longer aliphatic chains, phospholipids as liposomes, and related lipid compounds were found to display potent inhibition of the hemolytic activity of LGL granule cytolysin, with I 50 values in the range of 0.2–30 μ M. Soluble globular proteins inhibited LGL granule cytolysin hemolytic activity with I 50 of 0.07–0.4 mg/ml. However, lipoproteins were 2–3 orders of magnitude more potent inhibitors, with L 50 values of less than 1 μg/ml. The observed potent inhibition by lipid compounds lends support to a model of the lytic action of granule cytolysin in which soluble cytolysin molecules insert into the membrane lipid bilayer during the course of the lytic event.