Phosphorylation increases α-bungarotoxin binding to acetylcholine receptor-enriched membrane preparations
Acetylcholine receptor (AChR)-enriched membrane preparations from Torpedo electroplax bind α-bungarotoxin with a K(D) of 8.4 nM and the concentration of binding sites is 16 pmoles/mg protein. When, however, the α-toxin is incubated with receptor samples, phosphorylated in the presence of Mn2+ (10 mM) and ATP (0.5 mM), the concentration of binding sites is increased to 94 pmoles/mg protein, although there is no marked change in the K(D) (11 nM). Binding of acetylcholine to AChR-enriched membrane preparations occurs at a receptor which has two different conformational states with K(D)'s of 8.4 nM and 520 nM. The concentration of binding sites for the high affinity components is 1.35 pmoles/mg protein and for the low affinity component is 12 pmoles/mg protein. The effect of phosphorylation of the AChR on agonist binding could not be determined.