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Receptors alternate between resting↔ active conformations that bind agonists with low↔ high affinity. Here, we define a new agonist attribute, energy efficiency (η), as the fraction of ligand-binding energy converted into the mechanical work of the activation conformational change. η depends only on the resting/active agonist-binding energy ratio. In a plot of activation energy versus binding energy (an “efficiency” plot), the slope gives η and the y intercept gives the receptor’s intrinsic activation energy (without agonists; ΔG 0). We used single-channel electrophysiology to estimate η for eight different agonists and ΔG 0 in human endplate acetylcholine receptors (AChRs). From published equilibrium constants, we also estimated η for agonists of K Ca 1.1 (BK channels) and muscarinic, γ-aminobutyric acid, glutamate, glycine, and aryl-hydrocarbon receptors, and ΔG 0 for all of these except K Ca 1.1. Regarding AChRs …