FIGURE 2.
The ΔΔβ-toxins do not compete with site-4 toxins. A, rat brain synaptosomes were incubated 60 min at 22 °C with 0.1 nm 125I-Css4 and increasing concentrations of Css4, Bj-xtrIT, ΔΔBj-xtrIT, and ΔΔCss4. Nonspecific binding, determined in the presence of 1 μm Css4 (comprising 10% of total binding), was subtracted. The calculated Ki values were: Css4, 0.98 ± 0.1 nm (n = 8); Bj-xtrIT, ΔΔBj-xtrIT, and ΔΔCss4, >>10,000 nm. B, locust neuronal membranes (160 μg) were incubated with 0.1 nm 125I-Bj-xtrIT 45 min at 22 °C. Nonspecific binding, measured in the presence of 1 μm unlabeled Bj-xtrIT (comprising 30% of total binding), was subtracted. The Ki value of Bj-xtrIT was 1.6 ± 0.3 nm (n = 3); Css4, ΔΔBj-xtrIT, and ΔΔCss4, >>10,000 nm.