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. When the first oxygen molecule binds to one of the hemoglobin subunits, the affinity of the other three subunits to oxygen increases greatly. And this behavior of our enzyme is known as positive cooperativity. Now, hemoglobin not only displays positive cooperativity, it also displays something called negative cooperativity, which is basically the opposite of positive.