REPRESENTATION OF AFFINITY IN THE CASE OF COOPERATIVITY IN PROTEIN-LIGAND BINDING

We have already proposed a ''Global Association Function'' to represen t the global affinity of proteins to a drug; it was first applied in t he case of independent binding sites. In this paper, we show that this same function can also be used to assess interactions between sites b y varying the number of interacting sites and their co-operativity lev el. The resulting curves in two application cases are given together w ith the corresponding Scatchard plot: i) in a system with one single c lass of identical and interacting sites, ii) in a system with two clas ses of sites in which either primary or secondary are interacting; une xpectedly, in this latter case we also observed that sometimes positiv e co-operativity occasionally resulted in a concave-up Scatchard plot which is unusually admitted. In addition, as described in one example, our function is assumption free; this might be an advantage over usua l methods, such as discrete parameter methods, because they require ad ditional and empirical hypotheses on their related binding model.