Phospholipase A Activity in the Hemolysis of Sheep and Human Erythrocytes by Rickettsia prowazeki

Abstract

Incubation of Rickettsia prowazeki with sheep or human erythrocytes resulted in lysis of the erythrocytes and formation of free fatty acids and lysophosphatides. Inhibitors of lysis were also invariably inhibitors of this phospholipase A activity. The target for this activity was the glycerophospholipids of the erythrocyte and not those of the rickettsia. Rickettsial phosphatidylethanolamine labeled with 32 PO 4 or [ 3 H]acetate remained intact during lysis, and the composition of the free fatty acids released resembled that of the erythrocyte species used and not the rickettsiae. The products of hydrolysis remained associated with the sedimentable material in the reaction mixture under the usual conditions but partitioned into the supernatant fluid when bovine serum albumin was present. Initially, the time course of phospholipase A activity and lysis was identical, but the release of free fatty acids continued for a short time after the release of hemoglobin was complete. Both the inner and outer leaflets of the erythrocyte membrane were accessible to this rickettsial phospholipase A activity since both phosphatidylcholine and phosphatidylethanolamine were substrates in human erythrocytes. The questions of whether rickettsiae possess their own phospholipase A or activate a latent erythrocyte enzyme and what the role of the energy requirement is in these processes remain unanswered.