ABSTRACT
Divalent cations and polysaccharides such as inulin and dextran reversibly inhibited hemolysis of rabbit erythrocytes caused by Vibrio metschnikovii cytolysin. On the basis of the 50% inhibitory doses, the cations were divided into two groups, group I (Cd2+, Cu2+, Ni2+, Sn2+, and Zn2+) and group II (Ba2+, Ca2+, Co2+, Mg2+, Mn2+, and Sr2+). Neither divalent cations nor polysaccharides interfered with the binding of toxins to the erythrocyte membrane. Group I cations disturbed tetramer formation of cytolysin on the cytolysin-lysed erythrocyte membrane, although group II cations and dextran did not affect the process. Erythrocytes treated with cytolysin in the presence of group II cations or dextran lysed after transfer to toxin- and inhibitor (group II cations or dextran)-free buffer at both 37 and 4 degrees C. However, erythrocytes treated in the presence of group I cations lysed at 37 degrees C but not at 4 degrees C, indicating that group I cations block the temperature-dependent lesion (tetramer)-forming step subsequent to the binding of cytolysin to the erythrocytes. The cytolysin-treated erythrocytes swelled in a colloid osmotic manner, and the swelling was preceded by the binding and the lesion-forming steps. It is also suggested that the lysis of the erythrocytes proceeds in a temperature-independent manner and that the cytolysin does not bind to the erythrocytes at 4 degrees C. These findings suggest that the sequence of V. metschnikovii cytolysin-induced hemolysis is defined by three steps: (i) a temperature-dependent binding step, (ii) a temperature-dependent lesion-forming step, and (iii) a temperature-independent lysis step.
