Hemoglobin is a 66 kDa metalloprotein composed of four globular subunits each of which is associated with an iron-containing heme group. The heme group is involved with oxygen transport from the lungs to the tissues and the globin molecule plays a major role in transporting carbon dioxide in the reverse direction. Hemoglobin is found in the erythrocytes of all vertebrates. There is a wide diversity of amino acid sequences and substitutions within mammalian hemoglobins, however the molecular weight is generally around 66 kDa with an iron content of about 0.34 % . The level of hemoglobin in the blood is used in the diagnosis of anemia, levels in the feces are indicative of various clinical conditions.Synonyms: Haemoglobin