CROSS-LINKING OF MEMBRANE PROTEINS AND PROTOPORPHYRIN-SENSITIZED PHOTOHEMOLYSIS*

Abstract— Irradiation of protoporphyrin-sensitized red cells with blue light in the presence of oxygen alters many components of their membranes and eventually leads to hemolysis. Extensive cross-linking of membrane proteins can be observed before hemolysis occurs (Girotti, 1976).
Facile oxidative hemolysis can be achieved without observable cross-linking of membrane proteins upon incubation (37°C) of red cells containing membrane-bound 3ß-hydroxy-5α-hydroperoxy-△⁶-cholcstene. Thus, protein cross-linking is not obligatory for oxidative lysis. Deoxygenation by Ar bubbling strongly retards the light-induced increase in osmotic fragility and strongly inhibits eventual hemolysis of protoporphyrin-sensitized erythrocytes. However, similar reduction in oxygen concentration only partially inhibits cross-linking of membrane proteins. These results suggest that membrane protein cross-linking and photohemolysis are not coupled processes.