An empirical extremum principle for the Hill coefficient in ligand-protein interactions showing negative co- operativity

¹ Hebrew University

^* To whom correspondence should be addressed. E-mail: ahagai{at}agri.huji.ac.il.

Submitted on January 26, 2005
Revised on March 28, 2005
Accepted on 4 April 2005

	Abstract

The Hill coefficient (nH) is a central parameter in the study of ligand-protein interactions, which measures the degree of co-operativity between subunits that bind the ligand in multi-subunit proteins. The most common usage of nH is as an estimate of the minimal number of interacting binding sites in positively co-operating systems. In the present study, a statistical interpretation of nH 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 nH in negatively co-operating systems of identical binding sites, which can be used for the estimation of the minimal number of interacting sites in such systems.

Key Words: Hill coefficient, enzyme, ligand binding, negative co-operativity, protein

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