substitution of negatively charged glu-180 with uncharged gln in the calf peptide did not significantly affect toxin binding , indicating glu-180 alone does not comprise the anionic subsite on the receptor to which the cationic quaternary ammonium groups of cholinergic agents bind . d-tubocurarine competed toxin binding to the modified calf 32-mer which lacks glu-180 and asp-195 present in torpedo .
C0017797
gln
C0061472
glu