Involved in oxygen transport from the lung to the various peripheral tissues. Hemoglobin is composed of one globin plus four hemes, heme consists of protoporphyrin IX and ferrous iron. The iron content of human hemoglobin is 0.338 % (w/w) which gives a minimal molecular weight of 16,520, however, ultracentrifugal and osmotic pressure measurements indicate an actual molecular weight four times the minimum molecular weight.Synonyms: GHb, Hemoglobin A1c