Peptide extraction by alkaline treatment is accompanied by rearrangement of the membrane‐bound acetylcholine receptor from <i>torpedo marmorata</i>

Abstract

The ability to prepare membranes enriched in acetylcholine receptor protein (AChR) [ 1,2] constituted a significant contribution to in vitro studies of physiological significance (reviewed [3,4]).Work in this field has yielded evidence that the detergent-solubilized, purified AChR consists of subunits of 40 000 (a), 50 000 (p), 60 000 (r) and 65 000 (6) apparent InoIe~ular weight 131.The Mr 40 000 peptide carries the recognition site for acetylcholine and its analogues, a-toxins, and affinity labels of the nicotinic type [3].This subunit and a peptide of Mr 43 000 were reported to be the predominant components of the AChR-rich menlbranes [.5,6].More recently, it was suggested that the peptide of M, 43 000 (the v-band of [7]) carries the binding site for local anaesthetics and, by inference, the AChR-controlled channel [S].Yet, sizeable amounts of the ~-component ~ together with some other peptides, can be extracted at alkaline pH leaving an AChR-rich membrane with normal agonist and local anaesthetic binding capacities; the permeability control of the 22Na+ efflux is also retained [9].The role of the above Mr 43 000 peptide remains therefore elusive.A possible contribution of the Mr 43 000 peptide to the structure of the membrane has not yet been considered.The comparison of electron micrographs from untreated and alkaline-treated membranes yields significant differences in membrane organization, suggesting that the Mr 43 000 peptide may be important for stabilizing the AChR-rich menlbrane and the arrangement of the AChR protein in it.