ALTERATION OF HUMAN-ERYTHROCYTE PLASMA-MEMBRANES BY PERFRINGOLYSIN-O AS REVEALED BY FREEZE-FRACTURE ELECTRON-MICROSCOPY - STUDIES ON CLOSTRIDIUM-PERFRINGENS EXOTOXINS-V

When human erythrocyte membranes were treated with perfringolysin O (C. perfringens .theta.-toxin) and examined by EM after freeze-fracture, 2 ultrastructural alterations were observed in fracture faces of membrane. A random aggregation of intramembranous particles was seen in the fracture face of the protoplasmic half (PF face) of all membranes treated with the toxin, even if at a low concentration (40 hemolytic units/ml). The aggregation in the fracture face of the exoplasmic half (EF face) was observed only in membranes treated with a high concentration (3300 hemolytic units/ml) for 2 h. Round protrusions and ''cavities'' with 30 nm in diameter were visible in EF and PF faces of membranes treated with a high concentration, respectively. These structures were always protruded toward the cytoplasmic side but did not appear to form holes through the membrane. Ring and arc shaped structures with a dark center of 26 nm and a distinct border of 5 nm in width were observed when the toxin alone are negatively stained at a very high concentration (170,000 hemolytic units/ml). These structures were produced in the presence of cholesterol even if the toxin concentration was low.