These sites we call allosteric sites. And these allosteric sites are different than the active sites found on the enzyme that binds onto the substrate molecule. So we have special types of signal molecules, regulation molecules found inside our body that can bind onto these allosteric sites found on allosteric enzymes. And by binding they can create some type of change and that can actually alter the activity, the functionality of the enzyme. Now, allosteric enzymes and allosteric proteins basically observe something called Cooperativity. And we spoke about Cooperativity in detail when we discussed hemoglobin.