Haemoglobin is a type of globular protein present in red blood cells (RBCs), which transports oxygen in our body through blood. It is a tetrameric protein and contains the haem prosthetic group attached to each sub unit.
It is a respiratory pigment and helps in transporting oxygen as oxyhaemoglobin from the lungs to different parts of the body. Some amount of carbon dioxide is also transported back via haemoglobin as carbaminohaemoglobin.
Haem is an iron porphyrin complex.
The main function of Hb is to carry and transport oxygen to various tissues. The binding of oxygen to Hb is cooperative binding.
The binding and release of oxygen from Hb in the lungs and tissues respectively are due to the transition between low oxygen affinity T state (Tense) and high oxygen affinity R state (Relaxed).