Neuropharmacological characterization of fragment B from XXXX toxin.

@entity137 @entity3208 @entity19 @entity8776 @entity2975 @entity5819 @entity2195 @entity116
@entity116 toxin and Fragment B from @entity116 toxin were assayed for activity on the @entity19 phrenic nerve-hemidiaphragm preparation. Both molecules produced blockade of neuromuscular transmission, but the parent molecule was at least two orders of magnitude more potent than the fragment. Experiments were done to determine whether the @entity137 attributed to Fragment B was authentic or due to contamination with the parent molecule. Analysis of the fragment by high-performance liquid chromatography and by @entity2975 gel electrophoresis in the presence of @entity3208 revealed trace contamination. Removal of the major contaminant (1-2%) did not abolish @entity137 of the material. However, in pharmacological experiments with native toxin and its fragment, the latter behaved indistinguishably from the former. At equiactive concentrations, both were antagonized by @entity2195 and both were antagonized by lysosomotropic agents ( @entity5819 and @entity8776 ). In addition, monoclonal antibodies directed against epitopes in @entity2195 neutralized both native toxin and the material presumed to be Fragment B. The studies with antagonists and antibodies suggest that the @entity137 apparently associated with Fragment B was in fact due to trace contamination with the parent molecule. In experiments on planar lipid bilayers, Fragment B formed pH-dependent channels. This activity was not abolished by monoclonal antibodies directed against epitopes in @entity2195 . The data indicate that Fragment B retains the ability to form channels in membranes, but in the absence of @entity2195 it retains little ability to paralyze neuromuscular transmission.
