α‐Toxin binding to acetylcholine receptor α179–191 peptides: Intrinsic fluorescence studies

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Abstract
Interactions between two α‐toxins and the synthetic peptides α179–191 from both calf and human acetylcholine receptor α‐subunit sequences have been studied by measurements of quenching of intrinsic fluorescence after toxin addition. Dissociation constants of approx. 5 × 10−8 M for binding of calf peptide by both α‐cobratoxin and erabutoxin a have been estimated. The binding of α‐cobratoxin to calf peptide, which leads to marked quenching of fluorescence intensity, is inhibited by a 104 molar excess of acetylcholine. The human α179–191 peptide binds to α‐cobratoxin, but not, under comparable conditions, to erabutoxin a.