EFFECTS OF HETEROGENEITY AND COOPERATIVITY ON THE FORMS OF BINDING CURVES FOR MULTIVALENT LIGANDS

An exploratory investigation is made of the binding behavior that is l ikely to be encountered with multivalent ligands under circumstances w here a single intrinsic binding constant does not suffice to describe all acceptor-ligand interactions. Numerical simulations of theoretical binding behavior have established that current criteria for recognizi ng heterogeneity and cooperativity of acceptor sites on the basis of t he deviation of the binding curve from rectangular hyperbolic form for univalent ligands also apply to the interpretation of the correspondi ng binding curves for multivalent ligands. However, for systems in whi ch the source of the departure from equivalence and independence of bi nding sites resides in the ligand, these criteria are reversed. On the basis of these observations a case is then made for attributing resul ts of an experimental binding study of the interaction between pyruvat e kinase and muscle myofibrils to positive cooperativity of enzyme sit es rather than to heterogeneity or negative cooperativity of the myofi brillar sites.