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. So basically by binding one of the oxygen to only one of the subunits, that increases definitive of the other subunits for oxygen. And this cooperative behavior is known as positive cooperativity. So, hemoglobin, for example, contains four individual subunits that can each bind an oxygen molecule.