Alpha-toxin binding to acetylcholine receptor alpha 179-191 peptides: intrinsic fluorescence studies

Interactions between two alpha-toxins and the synthetic peptides alpha 179-191 from both calf and human acetylcholine receptor alpha-subunit sequences have been studied by measurements of quenching of intrinsic fluorescence after toxin addition. Dissociation constants of approx. 5 x 10(-8) M for binding of calf peptide by both alpha-cobratoxin and erabutoxin a have been estimated. The binding of alpha-cobratoxin to calf peptide, which leads to marked quenching of fluorescence intensity, is inhibited by a 10(4) molar excess of acetylcholine. The human alpha 179-191 peptide binds to alpha-cobratoxin, but not, under comparable conditions, to erabutoxin a.