What is Haemoglobin (Hb), Forms of Hb. Synthesis of Hb, Degradation of Hb, Complexes of Hb

 

Haemoglobin:-    

Haemoglobin is a chromoprotein consisting of a globin molecule attached to four red coloured haem molecules.  There are about 2-3 million Hb molecules in a red blood cells. The globin molecule consist of two alpha and two beta polypeptide chains. Haemoglobin is formed in the developing erythrocyte in the bone marrow. The life span of Haemoglobin is same as the life span of red blood cells 120 days.

 

click here to watch:-  what is Haematology

click here to watch:- what is blood and its cmposition

Synthesis of Haemoglobin:-

•    Haem synthesis occurs in mitochondria by a series of bio-chemical reactions.
•     Glycine + succinyl coenzyme A is condensed by delta amino laevulinic acid       (ALA) synthetase in the presence of pyridoxal phosphate(vitamin B6). This makes      the protoporphyrin.
•         Protoporphyrin combines with iron to make Haem.
•         Each molecules of haem combines with the globin chains on polyrobosomes.
•         Tetramer of 4 globin chains, each chain with its own haem group, make up of a        Haemoglobin  molecule.

 
Forms of Haemoglobin:-  

Different forms of Haemoglobin may occur in the red blood cells, depending on the content and sequence of amino acids in the globin chains.

·        Haemoglobin A (HbA)

·        Haemoglobin F  (HbF)

 

Haemoglobin A (HbA):- 

 HbA is the main haemoglobin & it contains 2 alpha and 2 beta chains.  HbA is present in adults 97%.

HbA₂    :-   

Another forms of haemoglobinAnother         HbA₂, it contains 2 alpha chains paired with 2 delta chains. HbA₂  present in small amounts (2-4%).

 

Haemoglobin F  (HbF):-  

In Haemoglobin F  two alpha chains are paired with two gamma chains. HbF is present 70-90% at birth, and it is major forms of haemoglobin during intrauterine life and at birth. HbF is slowly replaced by HbA . At the end of the first year, the HbF concentration is reduced to 1-2% in blood.

 

Degradation of Haemoglobin:-

The  degradation of haemoglobin begins in reticuloendothelial system. When the red blood cells completes its life span(120days), it is removed by the macrophages of the reticulo-endothelial  system. The haemoglobin is released, broken down, the useful portion is recirculated and the rest is excreted.

 

Complaxes of Haemoglobin:-

When haemoglobin is acted upon by the other chemicals, certain complexes of haemoglobin may be formed. These complexes may reduce its capacity to react with oxygen.

Such forms include:-

 ·      Carboxyhaemoglobin (HbCO)

·        Methaemoglobin (Hi)

·        Sulphhaemoglobin (SHb)

Carboxyhaemoglobin (HbCO):- 

When haemoglobin combines with carbonmonoxide HbCO is produced. It is found in higher concentration in the blood of smokers.

 

Methaemoglobin (Hi) :-

When haemoglobin reacts with certain drugs like sulphonamides then methaemoglobin is found.

 

Sulphhaemoglobin (SHb):-  

It is formed irreversibly by the action of certain drugs sulphonamides. Once it formed, it remains for the life of the carrier red blood cells and it is not capable of oxygen transport.