title: Binding of Clostridium botulinum type C neurotoxin to rat brain synaptosomes.
abstract: The binding of Clostridium botulinum type C neurotoxin to rat brain synaptosomes was determined by the use of 125I-neurotoxin. The binding was independent of the incubation temperature (0 degrees C and 37 degrees C) and was equilibrated in 10 min. The dose dependent of 125I-toxin binding to synaptosomes at 0 degrees C showed that there were two kinds of toxin receptors on the synaptosomal membrane; the association constants and maximum binding values were 1.05 x 10(10 M-1, 5.25 x 10(-13) mol/mg of synaptosomal protein and 5.00 x 10(6) M-1, 5.00 x 10(-12) mol/mg of synaptosomal protein, respectively. When the incubation of toxin with synaptosomes was continued at 37 degrees C after 125I-toxin had been pre-incubated with synaptosomes at 0 degrees C for 10 min, the displacement of labeled toxin by the addition of excess amounts of unlabeled toxin decreased slightly with increasing incubation time, and finally 0.4% of the bound 125I-toxin was not displaced from synaptosomes. The binding of 125I-toxin to synaptosomes was inhibited by anti-heavy chain IgG and a monoclonal antibody which neutralized toxin and recognized heavy chain. These results suggest that the binding sites of toxin to synaptosomes are localized on heavy chain and a small amount of the bound toxin is incorporated into the synaptosomal membrane or synaptosomes.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D001665:Binding Sites; D001905:Botulinum Toxins / Q000276:immunology / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D007074:Immunoglobulin G; D051379:Mice; D009498:Neurotoxins / Q000276:immunology / Q000378:metabolism*; D051381:Rats; D013570:Synaptic Membranes / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D007074:Immunoglobulin G; D009498:Neurotoxins; D001905:Botulinum Toxins