Exposure of human red blood cell membrane phospholipids to snake venom phospholipases A—I. Hydrolysis of substrates by Vipera palaestinae phospholipase from within resealed red cells

Hydrolysis of substrates by Vipera palaestinae phospholipase from within resealed red cells. Toxicon16, 145–152, 1978. In the absence of Ca²⁺ the phospholipase A of Vipera palaestinae venom is unable to degrade glycerophospholipids in intact and resealed human red cells, or in red cell ghosts. However, the substrates become available to the enzyme when the membrane structure is fully disorganized by treatment with detergents and sonication. Inside-out membrane vesicles and ghosts depleted of spectrin and actin are equally resistant to the action of the enzyme indicating that the phospholipids located at the cytoplasmic side are unavailable when directly exposed to the enzyme, even after removal of the protective protein layer. Partial hydrolysis of glycerophospholipids, mainly phosphatidylserine, occurs when the enzyme, present at the moment of hemolysis, becomes trapped within the membrane by restoration of isotonicity.