Hemolysis and splitting of human erythrocyte phospholipids by snake venoms

Abstract

1. 1. Lysis of washed human erythrocytes induced by Cobra snake venoms ( Naja naja, Hemachatus haemachate) was accompanied by splitting of the red-cell phospholipids to lysophosphatides. 2. 2. Phospholipase A fractions (phosphatide acyl-hydrolase, EC 3.1.1.4) isolated from the Cobra venoms were devoid of hemolytic activity and caused no significant breakdown of phospholipids in the intact erythrocytes. Another protein component derived from the same venoms (the direct lytic factor) was weakly hemolytic but showed no phospholipase activity. The two fractions, when combined, produced strong hemolysis and concomitant hydrolysis of erythrocyte phospholipids to lysophosphatides. 3. 3. Heparin or dextran sulfate, which were found to precipitate the direct lytic factor, abolished both the hemolytic activity of the Cobra venoms and their capacity for hydrolyzing the phospholipid constituents of the intact red blood cells. 4. 4. Viper venoms ( Vipera palestinae and Vipera russellii) containing phospholipase A but no direct lytic factor induced neither lysis nor substantial phospholipid splitting of washed erythrocytes unless fortified with the direct lytic factor fraction derived from Cobra venom. 5. 5. Treatment of the red blood cells with surface-active agents or sonic vibrations imitated the effect of the direct lytic factor in rendering the erythrocyte phospholipids susceptible to hydrolysis by phospholipase A. 6. 6. The various phospholipase A fractions studied could be differentiated into two types according to their abiltiy of hydrolyzing phospholipids in osmotic hemolyzates: the Cobra phospholipases which were active per se and the V. palestinae enzyme which required for its activity the addition of either the direct lytic factor or detergents or pretreatment of the osmotic ghosts by sonication. The Russell's viper venom was found to contain phospholipases of either type 7. 7. Some aspects, bearing on the mode of action of the various factors instrumental in rendering the membrane-bound phospholipids available to splitting by snake venom phospholipases A, are discussed. The role of these factors in the mechanism underlying the hemolytic activity and cell toxicity of the snake venoms is considered.