Question

State the effects of heterotropic and homotropic interactions on the equilibrium between the T and R forms of ATCase.

Answer 1

The effects of substrates (like aspartate) on allosteric enzymes (like ATcase) are referred to as homotropic effects

In contrast, the effects of nonsubstrate molecules on allosteric enzymes (like CTP and ATP on ATCase) are referred to as heterotropic effects

CTP inhibits the activity of ATCase. In the presence of CTP, the enzyme becomes less responsive to the cooperative effects facilitated by substrate binding; more substrate is required to attain a given reaction rate.

ATP too, is an allosteric effector of ATCase. However, the effect of ATP is to increase the reaction rate at a given aspartate concentration.