Kinetic Study on Streptolysin O*

Abstract

Studies were done on kinetics of hemolysis of rabbit erythrocytes induced by partially purified streptolysin O (SLO).*** An examination of the kinetics of hemolysis of rabbit erythrocytes by semilogarithmic plots of percent erythrocytes remaining versus time revealed the existence of lag phase and constant rate phase. The hemolytic rates observed at the constant rate phase were proportional to square of SLO concentration and decreased as the initial concentration of erythrocyte became higher. Cholesterol inhibited hemolytic activity of SLO when added before the incubation of SLO with erythrocytes. However, when added after the initiation of hemolysis, neither cholesterol nor hemolysates prepared by SLO treatment inhibited hemolytic activity of SLO. Independent of previous reduction with L-cysteine, SLO bound to cholesterol suspended in phosphate buffer and also to erythrocytes, while affinities of the reduced form of SLO for cholesterol as well as for erythrocytes were found higher than those of the unreduced form. Binding of the reduced form of SLO to erythrocytes was reversible at 4°C and SLO was transferable from erythrocyte to erythrocyte. However, once SLO had been bound to erythrocytes and hemolyzed them at 37°C, its hemolytic activity could not be detected with further addition of erythrocytes. On the basis of these observations, mechanism of cytolytic activity of SLO was discussed.