Multisubunit Structure and Amino-Terminal Sequences of Piscine Muscle Acetylcholine Receptor

The nicotinic acetylcholine receptor (AcChR) has been purified from both the electric organ and the muscle of the fish Electrophorus electricus. Upon SDS gel electrophoresis muscle AcChRs appeared to contain four main polypeptides whose molecular weights were similar but not identical to the molecular weights of the four peptides present in the electric organ AcChR. Each of these peptides has been isolated and their amino-terminal sequences have been determined. The AcChRs from muscle were found to be composed of four homologous proteins of apparent molecular weight 40,500, 50,000, 56,000 and 63,000, respectively. The subunit of Mr 40,500 is present in two copies for each AcChR molecule, while the other three components are present in one copy. No difference was found between the sequenced segments of corresponding subunits from muscle and from electric organ AcChR, suggesting that AcChRs in different tissues of the same animal are products of identical genes. The Electrophorus AcChR subunits are highly homologous with the corresponding subunits of Torpedo californica AcChR.