CHOLINERGIC SITES IN SKELETAL MUSCLE: INTERACTION WITH CONCANAVALIN A

Abstract– 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 macro-molecular 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^?9mol/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 ¹²⁵l-α-bungarotoxin binding to the partially purified acetylcholine receptor was blocked by unlabelled α-bungarotoxin, concanavalin A, d-tubocurarine and carbamylcholine.