SEPARATION OF CHOLINERGIC PROTEOLIPIDS FROM QUENCHED RAT CEREBRAL CORTEX AND RESOLUTION OF PROPERTIES AT LOW TEMPERATURE

Abstract

Proteolipids from rat cerebral cortex quenched at -196°C were extracted and fractionated at subzero temperature (-60°C). On Sephadex LH-20 column chromatography, acetylcholine and cholinergic blocking agents such as dimethyl-d-tubocurarine and decamethonium were observed to bind to different fractions of proteolipids showing that the receptor fractions for acetylcholine and that for cholinergic blockers need not be the same. The acetylcholinesterase (EC 3.1.1.7) activity was demonstrated to be absent in both types of receptor fraction. The specificities of binding by cholinergic substances to proteolipid fractions prepared at -60°C persisted at room temperature with some loss in specificity for acetylcholine. Since these specificities were not observed in previously reported experiments at room temperature, it appears that the structures of proteolipids extracted at the two temperatures differ. The appearance of specificities in the proteolipids prepared at low temperature suggest that their structures are in better approximation to those in vivo that presumably are highly specific. The importance of the protein moiety of proteolipids as a discriminator for the neurotransmitter is discussed.