And a single hemoglobin can carry a maximum of four oxygen molecules one in each one of these four hein groups. Now, when our hemoglobin is fully saturated with oxygen, we call it oxymoglobin. But when the hemoglobin isn't actually carrying any oxygen, in that case, we call it deoxyhemogglobin. Now, one important property of hemoglobin, one important property that hemoglobin actually exhibits is something known as positive cooperativity. Now, what exactly is positive cooperativity? Well, when one oxygen molecule is taken up by the hemoglobin, it causes a conformational change.