1. Introduction:
a. Hemoglobin structure:
Hemoglobin is metalloprotein found in red blood cells having four polypeptide chains. Adult hemoglobin contains 2 alpha (141amino acid) and 2 beta chains (146 amino acid) which forms a tetramer called as globin and each chain is attached to iron containing prosthetic group heme (protoporphyrine IX). Ferrous ion of this heme is linked to globular protein by binding ‘N’ in the center of the protoporphyrin ring. There is a non-covalent interaction between four chains. The four heme groups provide four binding sites for oxygen (Marengo; 2006)
As described by Max Perutz in 1959, the three dimensional structure of hemoglobin is similar to myoglobin but oxygen affinity in hemoglobin is more than that of myoglobin. Figure 1: Structure of Hemoglobin
(http://www.infobiochem.com/2014/12/Hemoglobin-and-its-defects.html)
Synthesis:
This complex protein molecule is synthesized in series of steps, it begins with synthesis of d-aminolevulinic acid (ALA) and porphobilinogen and then modification of terapyroll ring. The synthesis of heme part involves enzymes of mitochondria and
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This leads to excess beta globin chains in patient’s hemoglobin. The two genes HBA1 and HBA2 involved in this disorder are located on chromosome 16 (Williams et al., 1996, Allen et al., 1997). The normal genotypic representation of α-globin is αα/αα. There are two varieties of α-Thalassemia: α+ and α0 Thalassemia. The Heterozygotes form of α+ Thalassemia (−α/αα) is deficient of one linked α-globin gene. It is also known as Thalassemia minima. It is clinically normal and has negligible effect on hemoglobin synthesis, whereas homozygotes (−α/−α) produce low level of hemoglobin in erythrocytes which leads to microcytic hypochromic anemia. When both linked α globin genes are absent (−−/αα), the homozygous α0 Thalassemia state (−−/−−) is lethal (Weatherall,