Haemoglobin (Hb) is a metalloprotein which transports oxygen from the lungs through the blood stream.
In tissue, the oxygen is transferred to the oxygen binding protein myoglobin (Mb).
Haemoglobin has four subunits, the polypeptide chains α1, α2, ß1 and ß2.
Each of these chains contains one porphyrine macrocycle (iron-protoporphyrin-IX group).
Porphyrin macrocycle with its immediate environment