Effect of pH on the Haemolysis of Rabbit Erythrocytes by Staphylococcus Alphatoxin

The effect of toxin concentration on the kinetics of haemolysis of rabbit erythrocytes has been studied at pH values differing by about 0.5 pH units over the range 5.5 to 8.5 for both crude and partially purified toxin at concentrations of 2.5, 5.0, 10, 20, 30, 40, 60 MHD per ml and at 80 and 120 MHD per ml for the partially purified toxin.

Increased concentration of toxin caused a decrease in the prelytic lag time (τ) of the sigmoid haemolysis curves, a decrease in the time to reach 50 per cent, haemolysis (t1/2), and an increase in the maximum rate of haemolysis (Rm)

Plateaux in Rm-toxin concentration, τ-toxin concentration and t1/2-toxin concentration curves were found at all pH values : these were displaced to higher concentrations in plots drawn for the partially purified toxin.

The effect of pH on haemolysis is very marked, and pH profiles for the maximum rate of haemolysis were constructed : for the crude toxin, the shape of the profile changed as the toxin concentration was increased, while for the partially purified toxin the shape was independent of toxin concentration.

The pattern of the profiles indicates that the crude toxin contains a small concentration of impurity that is strongly lytic at pH 5.5 and less markedly so at 8.5; the impurity has no significant effect at intermediate pH values.

The reaction is first order with respect to toxin over a very small range of concentrations only, and the maximum rate of haemolysis is independent of toxin concentration at concentrations greater than 120 MHD per ml.

The reaction is first order with respect to erythrocytes at all pH values, and over all measurable concentrations.