Phosphorylation of membrane proteins at a cholinergic synapse.

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Abstract
Endogenous membrane protein kinase activity and protein kinase substrates were found in membrane fractions enriched in the acetylcholine receptor prepared from the electric organ of Torpedo californica. Phosphorylation of 4 polypeptides was stimulated 9-fold by K+. The specific cholinergic ligand, carbachol, inhibited phosphorylation of these 4 polypeptides by 72% in the presence of 1 mM Na+ and 100 mM K+. The 65,000 dalton component of the acetylcholine receptor in the membrane fraction appeared to be phosphorylated by the endogenous protein kinase. Protein phosphorylation may play an important role in synaptic events at nicotinic cholinergic synapses.