Binding of Cerebratulus cytolysin A-III to human erythrocyte membranes

Binding of Cerebratulus lacteus cytolysin A-III to intact human erythrocytes and erythrocyte membranes has been investigated. Binding to ghosts is essentially complete within 2.5 min of mixing which is slightly faster than the rate of hemolysis measured with intact cells. Approximately 4·10⁴ binding sites per cell, exhibiting a K_0.5 of 0.7 μM exist; this compares with 50% hematocrit of about 0.3 μM for A-III. Binding is absent in ghosts extracted with Nonidet P-40, but is unaffected by pretreatment of ghosts with either trypsin or elastase.