The Acetylcholine Receptor as Part of a Protein Complex in Receptor-Enriched Membrane Fragments from Torpedo californica Electric Tissue

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Abstract
The acetylcholine receptor from Torpedo californica electric tissue consisting of polypeptide chains of molecular weight 42000 (± 2000) is part of a protein complex. Cross-linking experiments with bifunctional reagents have shown that this complex has possibly a pentameric structure with a molecular weight of 270000 (± 30000). Besides the receptor subunit (α-chain), at least three further classes of polypeptide chains are part of the complex: β (Mr 48000), 7 (Mr 62000) and δ (Mr 68000). This can be shown by cross-linking the proteins extracted from receptor-enriched membrane fractions with a cleavable reagent: From the 270 000 molecular weight particle the four predominant polypeptide chains of the membrane, α, β, γ, and δ, can be obtained. The δ-polypeptide chains appear to form a dimer connected by an inter-chain disulphide bridge.