hæmoglobin

Hämoglobin, often spelled hemoglobin in English, is the iron-containing oxygen transport protein of red blood cells. It binds oxygen in the lungs and releases it in tissues, while also facilitating carbon dioxide transport from tissues to the lungs for exhalation. Hemoglobin is a tetramer composed of four globin polypeptide chains and four heme prosthetic groups. In adults the most common form is HbA, consisting of two alpha and two beta chains. Each chain surrounds a heme group with an iron ion that reversibly binds one oxygen molecule. The protein exhibits cooperative binding, producing a sigmoidal oxygen dissociation curve, and its affinity is modulated by pH, carbon dioxide, temperature, and the level of 2,3-bisphosphoglycerate.

Iron is supplied by diet and incorporated into heme during erythropoiesis in the bone marrow; globin chains are produced from globin genes. Mature red blood cells carry hemoglobin and lack nuclei. The average life span is about 120 days, after which hemoglobin is recycled by the spleen. Fetal hemoglobin (HbF, α2γ2) has higher oxygen affinity and replaces HbA in the fetus; HbA2 (α2δ2) is a minor adult variant.

Abnormal hemoglobins cause disease: HbS in sickle cell disease; thalassemias from reduced production of one globin chain; methemoglobinemia where iron remains ferric and cannot bind oxygen. Laboratory testing includes measurement of total hemoglobin and oxygen saturation, as well as electrophoresis or chromatography to identify variants. Hämoglobin testing is central to anemia evaluation.