Hemoglobin is a carrier, transporting oxygen from the lungs to
the tissues and the return transport of carbon dioxide.
Each hemoglobin molecule is made up of four heme groups
surrounding a globin group, forming a tetrahedral structure. Heme,
is composed of porphyrin to which an iron atom is attached.
- Hemoglobin can bind to oxygen by changing its spatial structure
from domed to planar.
- Allosteric effectors such as inositol hexaphosphate (IHP) bind
to deoxy Hb and HbCO(carboxy) at different sites, leading to a
lowered oxygen affinity
- hemoglobin ligands include competitive inhibitors such as
carbon monoxide and allosteric ligands such as carbon dioxide and
nitric oxide. The carbon dioxide is bound to amino groups of the
globin proteins to form carbaminohemoglobin. The nitric oxide
transport to peripheral tissues is said to assist oxygen transport
in tissues, by releasing vasodilatory nitric oxide to tissues in
which oxygen levels are low.
- Also, the binding of oxygen is affected by molecules such as
carbon monoxide. CO competes with oxygen at the heme binding site
and Hemoglobin binding affinity for CO is 250 times greater than
for oxygen that means small amounts of CO can reduce hemoglobin
ability to deliver oxygen to the target tissue.
- The binding of Oxygen by hemoglobin is regulated by H+, Carbon
dioxide and 2,3-bisphosphoglycerate