Pseudoconservative transition: a two-state model for the co-operative behavior of oligomeric proteins.

A plausible extension of the two-state concerted model is proposed. This extended two-state model involves at least one state with pairwise asymmetry and consequent heterogeneous binding properties. Such a pseudoconservative transition model accounts in a predictably restricted manner for either positive or negative co-operativity² and for a combination of both in the binding of a single ligand. State and saturation functions are derived. Variation of the Hill number with respect to the extent of binding provides a diagnostic test for the combination of both positive and negative co-operativities in ligand binding. Applications of the model to recent experimental data are discussed.