Conservation of the kinetic and allosteric properties of the acetylcholine receptor in its Na cholate soluble 9 S form: Effect of lipids

The rapid kinetics of interaction of the fluorescent cholinergic agonist Dns-C₆-Cho with the acetylcholine receptor protein (AChR) were followed by stopped-flow measurements. Dissolution of AChR rich membrane fragments from Torpedo marmorata by Na cholate and subsequent dilution in the absence of lipids resulted in the stabilization of the AChR in a state which exhibited a low affinity for Dns-C₆-Cho and could no longer be interconverted to the high affinity state in the presence of agonist. On the other hand, when the concentration of lipids was kept elevated in the presence of Na cholate, a soluble, 9S, low affinity form of the AChR was obtained which showed most of the characteristic properties of the membrane-bound AChR : in particular, the slow interconversion to the high affinity state and the effect of non-competitive blockers on this transition. After elimination of the detergent, this form lead systematically to successful reconstitution.