An Empirical Extremum Principle for the Hill Coefficient in Ligand-Protein Interactions Showing Negative Cooperativity

Abstract

The Hill coefficient ( n H) is a central parameter in the study of ligand-protein interactions, which measures the degree of cooperativity between subunits that bind the ligand in multisubunit proteins. The most common usage of n H is as an estimate of the minimal number of interacting binding sites in positively cooperating systems. In the present study, a statistical interpretation of n H for a generalized system of multiple identical binding sites is developed. This interpretation is then applied to the derivation of an empirical extremum principle for n H in negatively cooperating systems of identical binding sites, which can be used for the estimation of the minimal number of interacting sites in such systems.