Conversion of high affinity acetylcholine receptor from Torpedo californica electroplax to an altered form.

Most Triton extracts of fresh electroplax membranes showed a single kind of acetylcholine binding, of high affinity, with K_d = 17 nM. Fresh membrane preparations without Triton also showed only high-affinity binding (K_d = 14 nM), but membrane preparations from electroplax stored for 5 months in liquid nitrogen gave equal amounts of low-affinity binding material (K_d = 0.2 μM). Heating Triton extracts at 40 °C for 40 min or treating with 10^?4mp-chloromercuribenzoate or 5,5′-dithiobis(2-nitrobenzoic acid) converted the preparation to more than 90% low-affinity binding. It is suggested that the high-affinity is the native form and the low-affinity is an oxidation product.