Fig. 5. A rapid filtration method through DE-81 filters was used to measure the binding of ¹²⁵I--bungarotoxin (-Bgt) to affinity-purified acetylcholine receptors from electric rays at equilibrium. The data presented are from a typical experiment where the specific binding is plotted against increasing -Bgt concentrations. The dissociation constants calculated from the equation for a single binding site were not significantly different in the four electric rays tested, ranging between 21 and 53 nmol l^–1. Error bars represent S.E.M.