FIG. 2.

Effect of pH on the killer activity (○) or on the stability (●) of the purified killer protein from S. occidentalis. The change of pH values was adjusted with 0.1 M citrate phosphate buffer. The 100% killer activity is 500 aU, under conditions containing 0.4 μg of killer protein. To determine the optimal pH, the killer protein solution was adjusted to various pH values, and the killer activity of samples was then determined with the assay plate that had identical pH values. For pH stability, after incubation in different pH values at 24°C for 8 h, the pH value of samples was adjusted to a final pH of 4.4, and the residual killer activity was determined. Error bars represent the mean ± the standard deviation of the mean for duplicate samples.