Fig. 3. Purification of the acetylcholine receptor from the numb fish N. tasmaniensis. (A) The membrane fraction from the electric organ was treated with 1.5% Triton X-100, and solubilized material applied to the TDAC affinity column. Bound protein was eluted from the column using an increasing salt gradient. (B) The major contaminant (98 kDa) could be purified away from the acetylcholine receptor on an anion exchange column (ResourceQ), where it eluted later in the NaCl gradient. (C) The purified receptor ran close to the void volume on a Superdex200 gel permeation column (670 kDa), consistent with the receptor maintaining its dimeric form under the purification conditions used. Arrows indicate the elution positions of molecular mass markers used to calibrate the column: 670, 158, 44, 17 and 1.35 kDa. Absorbance was measured at 215 nm in A and C and at 280 nm in B.