ABSTRACT
Hemoglobin and myoglobin are the two oxygen-binding proteins present in large multicellular organisms. Hemoglobin transports oxygen in the blood and is located in the erythrocytes; myoglobin stores the oxygen in the muscles. Myoglobin was the first protein to have its three-dimensional structure solved by X-ray crystallography. The heme prosthetic group in myoglobin and hemoglobin is made up of a protoporphyrin IX ring structure with an iron atom in the ferrous oxidation state. Hemoglobin is an allosteric protein. In the fetus there is a different kind of hemoglobin, hemoglobin F (HbF) which consists of two α-chains and two γ-chains, in contrast to adult haemoglobin. HbF binds 2, 3-bisphosphoglycerate less strongly than adult hemoglobin and thus has a higher affinity for O2 which promotes the transfer of O2 from the maternal to the fetal circulation. Several hundred abnormal hemoglobins have been characterized, giving rise to the so-called hemoglobinopathies. Probably the best characterized hemoglobinopathy is sickle-cell anemia.
