FIG. 9.

Titration of ADP-ribosyltransferase-inhibiting antibodies. Anti-ETA and antipeptide 6 (Anti-pep6) antibodies (2 mg/ml) were serially diluted and incubated with ETA (20 ng per reaction mixture) for 1 h at 37°C. ETA was then activated, and the reaction mixture was incubated for 15 min at 25°C. The reaction was stopped with 10% TCA, and the samples were counted with a beta scintillation counter. Inhibition of activity was expressed as the percentage of activity measured in the absence of antibody. Spontaneous ADP-ribosylation of eEF-2 in the absence of ETA was deducted from the actual values obtained. Results represent the mean ± standard error of two independent experiments, with each experiment performed in duplicate.