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

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Abstract
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.