Biochemical characterization of solubilized muscarinic acetylcholine receptors

Several in part new methods (salt extraction, phospholipase treatment, transfer to serumlipoproteins, nonionic detergent mixtures) have been extensively examined in order to obtain a solubilized muscarinic acetylcholine receptor with properties suitable for further purification. An optimal mixture of digitonin and gitonin has been found which forms a tightly bound detergent wall around the receptor protein as indicated by ion exchange and monolayer studies and which allows to solubilize the receptor from enriched synaptosomal membranes with a high yield and stability. The specific 3H-QNB binding of this preparation is nearly unchanged between pH 7.5 and 10. The isoelectric point of the muscarinic acetylcholine receptor has been determined by isoelectric focusing to be between pH 4.5 and 4.6.