Now one other type of regulation that I'd like to discuss that also deals with allosteric sites is known as enzyme Cooperativity. So basically certain enzymes can also display this phenomenon known as Cooperativity. And before we define what this actually is, let's take a look at an example at a biological enzyme that displays this concept of Cooperativity. So this enzyme is hemoglobin. So hemoglobin is a protein that consists of four subunits and each one of these subunits contains a heme group that is capable of binding a single diatomic oxygen molecule so that a hemoglobin can bind a total of four individual diatomic oxygen molecules. Now when our hemoglobin binds one of the oxygen onto one of the subunits by binding that first oxygen molecule, that increases the affinity for oxygen for the other three different subunits.