The Relationship between Cholinergic Proteolipid and Proteodetergent in Torpedo Electroplax Membranes

Abstract

The two methodological approaches used for the separation of the cholinergic receptor from electric tissue: i. e. organic solvents (De Robertis et al., 1967, LaTorre et al., 1970) or detergent extraction (Changeux et al., 1970; Miledi et al., 1971) have led to the isolation of hydrophobic intrinsic proteins from the electroplax membranes. Because of the intimate relationship of these proteins with lipids, in one case, or detergents, in the other, here they will be called “cholinergic proteolipid” and “cholinergic proteodetergent”. The problem which will be considered is that of the identity or non-identity of these proteins; in other words if they are totally different or if they have some similarities. Because both the proteolipid and the proteodetergent have high affinity binding for cholinergic agonists and antagonists of nicotinic type and could be separated from acetylcholinesterase (De Robertis and Fiszer de Plazas, 1970), we were inclined to think that they were similar or at least partially related (Fiszer de Plazas and De Robertis, 1972). Later on, since most of the work on the proteodetergent was based on α-bungarotoxin we studied the binding on this α-toxin to the proteolipid from the electroplax. We found that α-bungarotoxin displaced the site of high affinity for the cholinergic fluorescent probe dansylcholine (De Robertis and Barrantes, 1972). Furthermore, it was possible to demonstrate the binding of labeled α-bungarotoxin to the proteolipid by the use of Sephadex LH 20 chromatography. In experiments done on the electroplax membranes extracted with organic solvents, the membranes lost the binding capacity for α-bungarotoxin, while there was binding to the extracted proteolipid (Fiszer de Plazas and De Robertis, 1972).