Studies of the composition of purified Torpedo californica acetylcholine receptor and of its subunits

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Abstract
Under conditions that limit proteolytic degradation, the detergent-solubilized purified receptor protein from Torpedo californica electric organ exists in monomeric and dimeric forms. The purified receptor complex is composed of 4 different polypeptide subunits of apparent MW 40000 50000, 60000, and 65000. The individual polypeptides were purified and their amino acid compositions were relatively hydrophobic. The carbohydrate composition of the intact receptor complex and of the individual polypeptides was determined. Amino acid analysis provided evidence for the occurrence of a component with chromatographic properties similar to those of phosphoserine. Treatment of receptor with CH3NH2 in base, a condition which provided quantitative modification of O-phosphoserine residues in .beta.-casein, completely eliminated the peak corresponding to phosphoserine following mild acid hydrolysis. The receptor contains O-phosphoserine residues to the extent of approximately 7 residues per molecule and these residues occur in all constituent poypeptides. Other forms of O-substituted serine and threonine occur were probably observed as glycosylated residues.