Unified theory for a receptor system with a distributed binding affinity to substrates

► We report a theory for an objective characterization of a substrate-receptor system with an arbitrary binding affinity distribution. ►We propose a quantitative analysis method applicable to a heterogeneous receptor system with use of a novel experimental plot, named Θ0 plot. ►Our analysis method enables one toestimatekey physical parameters that mostly determine the shape of the bound fraction isotherm.