Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.10.13.337410v1?rss=1 Authors: Indurthi, D., Auerbach, A. Abstract: Concentration-response curves (CRCs) are characterized by a midpoint (EC50) and a high-concentration asymptote (POmax) that relate to agonist affinity and efficacy. A third agonist attribute, efficiency, is the fraction of binding energy that is applied to the conformational change that activates the receptor. Here we show that agonist efficiency can be calculated from EC50 and POmax, and estimate the efficiencies of 17 agonists of adult muscle nicotinic acetylcholine receptors (AChRs). The distribution of efficiency values was bi-modal with mean{+/-}s.d of 52{+/-}2% (n=11) and 41{+/-}3% (n=6). Efficiency is correlated inversely with the volume of the agonists' head-group. For 22 binding site mutations only aY190A affects significantly ACh efficiency, switching it from the high- to the low-efficiency population. If agonist efficiency is known, EC50 can be estimated from POmax and the receptor's level of constitutive activity can be calculated from a CRC. Copy rights belong to original authors. Visit the link for more info