Binding to and hemolysis of human erythrocytes by pyrularia thionin and Naja naja kaouthia cardiotoxin: inhibition by prothrombin.

Pyrularia thionin and snake venom cardiotoxin are strongly basic proteins which bind to and induce hemolysis of erythrocytes, cause depolarization of muscle cells, and influence the order and properties of phospholipids in cellular membranes. Earlier studies showed a competition between the thionin and cardiotoxin for a common binding site on erythrocytes, and the present study extends these studies to show a similar competition between prothrombin and both basic proteins. The competition between the thionin and prothrombin for binding sites on erythrocytes was shown by direct binding experiments using radiolabeled thionin. Whereas binding of thionin or cardiotoxin induces hemolysis as a consequence of membrane perturbation, prothrombin does not induce hemolysis. Although it binds to the same site, there is no penetration into and perturbation of the membrane. The competition between prothrombin and pyrularia thionin is not influenced by added Ca++. This indicates that membrane PS interacts in a specific and Ca++-independent manner with at least one site on prothrombin, as proposed earlier (Tendian and Lentz, 1990). The competition between thionin and prothrombin was also demonstrated for the release of radiolabeled chromate from loaded P388 cells. The competition observed with the P388 cells shows that the competition is not a unique phenomenon with erythrocytes, but occurs with other cell membranes.