hemoglobini

Hemoglobini is a heme-containing protein located in the red blood cells of many vertebrates. Its primary role is to transport oxygen from the lungs to tissues throughout the body and to carry a portion of carbon dioxide, a waste product of metabolism, from tissues back to the lungs for exhalation. The molecule consists of four globin subunits and four heme groups, each heme containing an iron ion that reversibly binds one O2 molecule. In humans, the most abundant form in adults is hemoglobin A, a tetramer of two alpha and two beta chains; other forms include hemoglobin A2 (two alpha and two delta chains) and fetal hemoglobin (HbF; two alpha and two gamma chains), which have distinct oxygen affinities and developmental expression patterns.

Oxygen binding by hemoglobini is cooperative: binding of oxygen to one heme increases the affinity of the remaining sites. The affinity is modulated by factors such as pH (the Bohr effect), carbon dioxide levels, temperature, and 2,3-bisphosphoglycerate (2,3-BPG). In the lungs, hemoglobini loads O2; in tissues, it releases O2 and binds CO2, which is transported to the lungs for expiration. Some CO2 is carried as carbaminohemoglobin, and a large portion is transported as bicarbonate in plasma after conversion by carbonic anhydrase.

Hemoglobini is synthesized in bone marrow erythroid cells from several globin gene families, including HBA1, HBA2, and HBB. Abnormalities in globin production or structure can cause disorders such as thalassemias and hemoglobinopathies; the most well-known example is sickle cell disease, caused by a point mutation in the beta-globin gene that promotes polymerization under low oxygen. Diagnosis often involves measuring hemoglobini concentration and using electrophoresis or genetic testing.