Sequential model

The sequential model (also known as the KNF model) is a theory that describes co-operativity of proteins subunits.

Overview
This model suggests that the subunits of multimeric proteins have two conformational states. The binding of the ligand causes conformational change. Although the subunits go through conformational changes independently (as opposed to in the MWC model) the switch of one subunit makes the other subunits more likely to change, by reducing the energy needed for subsequent subunits to undergo the same conformational change. In elaboration, the binding of a ligand to one subunit changes the proteins shape, thereby making it more thermodynamically favourable for the other subunits to switch conformation to the high affinity state. It's named KNF after Koshland, Némethy and Filmer.