Possible modulation of phosphorylation of acetylcholine receptor-enriched membrane preparations.

During phosphorylation of acetylcholine receptor (AChR)-enriched membrane preparations from Torpedo fuscomaculata , phosphate is incorporated into a single protein, with a molecular weight corresponding to that of one of the receptor subunits (37,000 daltons). This protein also seems to contain the receptor binding site. ATP binds to four protein species, one of which corresponds to a different subunit of the receptor (molecular weight 45,000). Phosphorylation of these membrane preparations is affected by several factors, known to be involved in postsynaptic events. Ca2+ (10 microM) inhibits the reaction, whereas cGMP (20 microM), causes stimulation. Furthermore it has been shown that the agonists, acetylcholine, and carbamylcholine (10 microM and 1 microM) stimulate the phosphorylation reaction, while the antagonists, tubocurarine, hexamethonium, and decamethonium (1 microM), cause inhibition.