In enzymology, Cooperativity is a phenomenon in which the shape of one subunit of an enzyme consisting of several subunits is altered by the substrate or some other molecule so as to change the shape of a neighbouring subunit. If the change in shape of the first subunit makes easier the binding of substrate to the second subunit, the effect is called positive cooperativity. In negative cooperativity, the binding of a molecule to the first subunit makes more difficult the binding of substrate to the second.