This means that an enzyme with quaternary structure can bind more than one substrate molecule. Allosteric enzymes change shape between active and inactive shapes as a result of the binding of substrates at the active site, and of regulatory molecules at other sites. ATCase catalyzes the condensation of aspartate and carbamoyl phosphate to form carbamoyl aspartate. ATP is an activator for this reaction and CTP is an inhibitor of the reaction. Allosteric enzymes may also have regulatory subunits that bind either activators or inhibitors.
Inhibitors cause the allosteric enzyme to adopt the inactive shape.
Activators promote the active shape. An equilibrium exists between the active and inactive shapes. The amount of active and inactive enzyme is dependent on the relative concentrations of substrate and inhibitor, as suggested by the diagram. An excess of substrate can overcome the inhibitor effect. Regulatory subunits bind activators or inhibitors effectors reversibly and alter the catalytic subunit's ability to bind substrate and catalyze conversion to product.