Figure 8.
Energetics of the phenomenological model for AChR activation, desensitization, and recovery. (top) The cyclic reaction (C, closed; O, open; and D, desensitized). For simplicity, the two agonist binding steps have been condensed. The numbers are ΔG O values (k B T ) and were calculated from the ratios of the rate constants shown in Model IV. The sign of the ΔG O value pertains to the clockwise direction. (bottom) Graphical representation of the reaction free energies of the states. Unliganded closed is the ground state and [ACh] = 1 M. The A2D state is the most stable, and only the D state is less stable than the C state. Desensitization has opposite energetic consequences in diliganded (stabilizes) and unliganded (destabilizes) AChR.