1. 1.|Pancreatic phospholipase A2 (phosphatide acyl-hydrolase, EC 126.96.36.199) and phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 188.8.131.52) from Bacillus cereus appeared not to be lytic for human erythrocytes, either before or after treatment of the cells with trypsin, pronase or neuraminidase. No significant breakdown of phospholipids could be observed.\ud \ud 2. 2.|Both phospholipases were found to evoke hemolysis in the presence of sublytic concentrations of sodium deoxycholate, whereas sublytic concentrations of Triton X-100 were effective only in combination with phospholipase C.\ud \ud 3. 3.|Treatment of human red cell ghosts with either phospholipase A2 or phospholipase C resulted in a complete hydrolysis of lecithin, phosphatidylethanolamine and phosphatidylserine, whereas sphingomyelin was not attacked. Similar results were obtained with liposomes derived from human erythrocytes, indicating that the degree of hydrolysis depends only upon the chemical nature of the phospholipids involved.\ud \ud 4. 4.|In the native human erythrocyte membrane the fatty acid-ester linkage at C2 and the phosphoryl-glycerol linkage at C3 of the phosphoglyceride molecules apparently are not accessible to phospholipase A and C attack. Removal of the sialic acid residues from the membrane surface does not promote the action of these lipolytic enzymes. Changes in membrane architecture occurring during membrane isolation or as induced by nonlytic concentrations of detergents lead to exposure of membrane phosphoglycerides to phospholipases A and C
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