Exposure of human red blood cell membrane phospholipids to snake venom phospholipases. A—II. Hydrolysis of substrates in intact and resealed cells by phospholipase from Ringhals ( Hemachatus haemachates) venom: Effect of calcium ions

Abstract

Hydrolysis of substrates in intact and resealed cells by phospholipase from Ringhals ( Hemachatus haemachates) venom: Effect of calcium ions. Toxicon 16, 153–161, 1978. The accessability of glycerophospholipids in intact and in resealed human red cells to the action of Ringhals phospholipase A has been compared in isotonic and in hypotonic conditions, both with and without addition of Ca 2+. Normal red cells in hypotonic media exposed prior to hemolysis, up to 70% of the membrane phosphatidylcholine, 20% of the phosphatidylethanolamine and about 5% of the phosphatidylserine to the action of the enzyme. The rate of hydrolysis of individual substrates in red cells in non-hemolytic conditions differs from the characteristic substrate preference of the enzyme. It is concluded that, in the outer half of the intact membrane, phosphatidylcholine is more exposed than phosphatidylethanolamine. The limit of non-lytic phospholipid degradation varies with the extent of stress exerted on the membrane by osmotic swelling and is strongly influenced by the presence of Ca 2+ which acts both as an enzyme activator and a membrane stabilizer. Both in isotonic and in hypotonic media resealed cells differ from the normal ones by exhibiting an increased availability of the membrane glycerophospholipids, particularly phosphatidylserine and phosphatidylethanolamine, to the action of the enzyme. Moreover, while in isotonic media intact cells are not hemolyzed by the enzyme either in absence or in the presence of added Ca 2+, the resealed cells treated with enzyme and Ca 2+ undergo hemolysis.