Structure and Function of Hemoglobin in animals

Structure and Function of Hemoglobin in animals

Hemoglobin is the iron-containing oxygen-transport metalloprotein present in the red blood cells of all vertebrates that carries oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs

The oxygen carrying capacity of hemoglobin is 60% more than that of plasma.

It also functions as a buffer in the regulation of acid base balance.

A hemoglobin molecule is a  complex substance consisting of conjugate protein composed of a pigment heme and a protein, globin.

The protein portion of each of these chains is called “globin”. The a and b globin chains are very similar in structure. In this case, α and ß refer to the two types of globin.

 The globin is a conjugated protein and heme contains iron in ferrous state.

Hemoglobin contains four polypeptide chains namely two alpha and two beta chains. Each of the four chains unites with a heme group resulting in a hemoglobin molecule. 

Concentration of hemoglobin in various species

Types of Hemoglobin

Based on physiological functions, the hemoglobins are typed as adult hemoglobin and fetal hemoglobins. Electrophoretically, the Hbs are classified as HbA, HbB, HbC and HbF. Human beings show three types of Hb, HbA (98%), HbA2 (2%) in the adult and HbF in fetus and new born. HbA has 2 µ -chains and 2 ß -chains; HbA2 is represented by 2 µ and 2 delta – chains. HbF has 2 µ -chains and 2 γ -chains.

In adult sheep HbA (2 µ , 2 ß) is electrophoretically fast and has higher O2 affinity than HbB with 4γ chains. Sheep having HbA or HbB under anemia or hypoxic condition develop another type of Hb, the HbC, which partially or completely replaces the HbA. Such a change is also observed in goat. HbC is the naturally occurring Hb in sheep during growth period. HbF has higher affinity for O2. In many animal species fetal hemoglobin (HbF) is replaced by the adult types with in 4 to 8 weeks after birth. In adult cat the HbA and HbB are found in the same ery­throcyte.

Some of the Hb variants, HbS, HbC, HbE are associated with specific hematologic disorders. HbS is responsible for sickle-cell anaemia in Negro race. HbC and HbE cause failure of synthesis of alpha or beta chains thus results in alpha or beta thalassemia.