Hemoglobin

The major function of hemoglobin in vertebrates is to bind oxygen in the lungs and transport it to the tissues. Since there is only a threefold to fivefold difference in the normal oxygen concentration between the lungs and the tissues, cooperativity in the affinity for oxygen is necessary to achieve efficient delivery of oxygen. This cooperativity results mainly from a conformational change in the quaternary structure of the hemoglobin tetramer, and is strongly influenced by various effectors. There are two types of effectors. Bisphosphoglycerate (BPG) and inositol hexa(kis)phosphate (IHP) are normally at fairly constant concentrations, and have become agents that weaken the affinity of hemoglobin for oxygen. There are also some appropriate physiological effectors, carbon dioxide and protons, that increase during an anaerobic/anoxic state, and by further lowering the affinity for oxygen, increase the ability of hemoglobin to release oxygen to active tissues that have an increased need for oxidative metabolism.