Abstract
1 Muscarinic receptors from the brain of rat, guinea-pig and frog have been labelled with tritiated propylbenzilylcholine mustard ([3H]-PrBCM). 2 After solubilisation and sodium dodecyl sulphate (SDS)-polycarylamide gel electrophoresis a single radiolabelled peak was seen which was completely suppressed when labelling was carried out in the presence of 10(-6) M atropine. The results suggest the presence of a single polypeptide chain with a molecular weight of similar to or approximately 80,000. 3 In the case of intestinal smooth muscle multiple labelled peaks were found. Precautions against proteolysis led to the identification of a major peak with a molecular weight in the region of 80,000.