Protoporphyrin IX acts as a sensitizer in the photohemolysis of bovine erythrocytes by binding to a limited number of membrane sites. The cholesterol-specific antibiotic lucensomycin competes with protoporphyrin in binding to the membranes. The possibility of cholesterol peroxidation as a primary event in photohemolysis is supported by the repairing effect of exogenous cholesterol and by the increased susceptibility of the photosensitized erythrocytes to lucensomycin. Glutathione, if present within the erythrocyte, postpones the onset of lysis; if added after irradiation, it may repair the membrane damage and prevent hemolysis. This effect appears to be related to a redox reaction (possibly involving glutathione peroxidase) between reduced glutathione and the cholesterol peroxide molecules.
