Aspects of the structures of isolated acetylcholine receptors from the electric tissue of Electrophorus electricus and Torpedo californica will be compared. The constituent polypeptide chains of each will be isolated and sufficient primary structure determined to establish similarities and dissimilarities. Initial efforts using the affinity label, 4-(N-maleimido) benzyltri (H3) methylammonium ion, have shown similarities between the polypeptide chains bearing the acetylcholine binding site and apparent differences in other constituent chains. The stoichiometry and proximity of the chains in the receptors will be determined by standard methods, including cross-linking and hybridization. The disposition of the chains in native and reconstituted membranes will be probed using immunocytochemical techniques. Evidence for transitions in the tertiary and quaternary structure of receptor will be sought be determining the effects of the binding of acetylcholine and congeners on the chemical and physical properties of receptor in solution and in membrane. The contributions of individual chains to function will be investigated by chemical modification and reconstitution. This research will contribute to the understanding of mechanisms of permeability control of synaptic membranes by acetylcholine receptors.