HEMOGLOBIN STRUCTURE
Hemoglobin is the major oxygen carrying molecule was the first oligomeric protein to be studied by X- ray diffraction methods.
Two major types of hemoglobin occur in humans at different stages of development namely,Feotal Hemoglobin(Hb F),and Adult hemoglobin(Hb A). Other forms of hemoglobin such as embryonic and minor adult forms do exist.
Each molecule of hemoglobin is composed of four polypeptide chains plus a heam group.hemoglobin A contains two identical alpha chains and two identical beta-chains.There is another type of hemoglobin A which contains sigma chains.
Before birth several additional hemoglobin polypeptides are synthesized e.g., In early embryonic life hemoglobin show presence of Epsilon chain while in the fetal life it shows the presence of two alpha chains.While in the fetal life it shows the presence of two alpha chains and two sigma chains because both hemoglobin in embryonic life and hemoglobin in fetal life have grater affinity for oxygen than hemoglobin in adult life.The feotus can prefentially absorb from maternal blood streams.
Each peptide chain whether alpha,beta or sigma is encoded by a specific gene.Hb F present in developing feotus is normally replaced by Hb Awithin the 1st 6 monthsafter birth.Each polypeptide consists of specific sequence of a specific sequence of AA's.
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