ABSTRACT
If the enzyme-substrate complex ES is formed in a rapid equilibrium, authors can define the dissociation constant of the ES complex, kS, as Ks=[E][S][ES] and obtain [ES]=[E][S]Ks for the concentration of ES in equilibrium. The Michaelis-Menten formalism assumes a true thermodynamic equilibrium between enzyme and substrate and the enzyme-substrate complex ES. Consider a reaction where a basic group on the enzyme needs to be protonated to catalyze a reaction. In this case, the reaction velocity will depend on the fraction of the enzyme that is protonated. The rate equations for enzymes with one or more active sites become different when the individual active sites of the enzyme interact with each other. The interaction between two active sites can be positive or negative: the binding of substrate to one active site can promote or inhibit binding of a second substrate molecule to the second active site.
