CHOLINERGIC SITES IN SKELETAL MUSCLE: INTERACTION WITH CONCANAVALIN A

The interaction of normal and denervated skeletal muscle cholinergic sites with the lectin concanavalin A and concanavalin A Sepharose are detailed. Concanavalin A blocks the binding of ¹²⁵I α bungarotoxin to both the high and low affinity sets of cholinergic sites described previously. The characteristics of the block of ¹²⁵I α bungarotoxin binding to the high affinity set (acetylcholine receptor) is not competitive. The data suggest that the concanavalin binds multivalently to the macromolecular complex containing the ACh receptor site and sterically prevents the α bungarotoxin binding. The interaction of both sets of cholinergic sites with concanavalin A Sepharose was also studied. The macromolecule(s) containing both the high and low affinity sets of sites bind to the concanavalin A Sepharose. The data indicate a multivalent association with the affinity resin. Following the affinity procedure, a partial purification in both sets of sites is effected. The equilibrium binding of ¹²⁵I diiodo α bungarotoxin to the preparations from the affinity procedure (both normal and denervated muscle) was examined. The K(D) of the α bungarotoxin binding to the high affinity sets of sites (acetylcholine receptor) in both normal and denervated preparations changes from ∞10^-9 mol/l to ∞10^-10 mol/l following purification. No change in the K(D) of the α bungarotoxin binding to the low affinity set of sites was observed following purification. The ¹²⁵I α bungarotoxin binding to the partially purified acetylcholine receptor was blocked by unlabelled α bungarotoxin, concanavalin A, d tubocurarine and carbamylcholine.