Figure 9.

The affinity of the wild-type AChR's closed state for choline. (A) Structures of choline and ACh. (B) The K_D values for ACh and choline were estimated by globally fitting Eq. 6 to the entire experimental dataset of an activation-competition assay. K_{D, ACh} and K_{D, Choline} were estimated to be 106 ± 6 μM, and 4.1 ± 0.5 mM, respectively. The other parameters in Eq. 6 were fixed as follows: θ₂ = 25, ρ₂ = 0.035, and η₂ = (θ₂ρ₂)^0.5 = 0.935. Two views of the same 3-D plot, rotated by 100°, are shown. (C) Data displayed as 1-D concentration–response plots, with the concentration of choline in the pipette fixed at the indicated values. Note that the solid lines were calculated using the parameters obtained from the global fit. (D) Data displayed as 1-D concentration–response plots, with the concentration of ACh in the pipette fixed at the indicated values. The solid lines were calculated using the parameters obtained from the global fit. Vertical error bars in C and D are standard errors.