Interrelationship of carbohydrate and the alpha-toxin binding site on the acetylcholine receptor from Torpedo marmorata

The relationship of the carbohydrate components of purified acetylcholine receptor (AChR) to its acetylcholine binding site was investigated by two approaches. In the first, the effect of periodate or glycosidase treatment of AChR on its ability to bind α-bungarotoxin was assessed. Although loss of binding capacity was observed, this could be attributed to increased temperature, acid pH or high salt concentrations of the incubation conditions rather than to the specific action of periodate or glycosidases, indicating that the α-toxin binding site does not directly involve carbohydrate.The second approach involved the use of concanavalin A to block the binding of α-toxin to AChR, when a maximum inhibition of approximately 40% was obtained. The results are interpreted in terms of heterogeneity of AChR molecules, of which some 40% have sterically interacting sites binding concanavalin A and α-toxin respectively.