Light Chains:
The sequencing of light chain revealed that there are two types of light chains namely “Kappa (K)” and “Lambda (L)” type. Each of the immunoglobulins has either a pair of Kappa or Lambda but not the mixture of two.
About 60% of serum immunoglobulins contain K type light chains and the remaining 40% immunoglobulins have Lambda type light chains. Whether lambda type or Kappa type, each light chain holds a constant domine towards the carboxy terminal and a variable domine towards the amino terminal of polypeptide chain. Generally each domine comprises about 100-110 amino acids.
The constant region or constant domine of light chain is represented as “CL” and variable region is represented as “V, “. Each domine is considered as a unit and an intra disulphide bond in each unit makes a loop, with about 60 amino acids in each domine.
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Heavy Chains:
Analysis of heavy chain sequence shows presence of three or four constant domines towards carboxy terminal and a single variable domine towards amino terminal regions of polypeptide chains.
Like that of light polypeptide chain, each domine contain an intra disulphide bond. The constant domines are referred and the variable domine is referred as VH domine.
Each variable domine enclose about four hyper variable sites or hotspots. The hyper variable sites are also known as complementarity determining regions (CDRS). The constant domines participate in various biological functions in accordance with the amino acid sequence.
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The CHI constant domine next to the variable domine serve to extend and bend the variable domine in various angles to interact with antigens. There are five types of heavy chains, designated by Greek letters namely a (alpha), 8 (delta), e (epsilon), 8 (gamma) and p (mu).
With reference to the type of heavy chain, immunoglobulins are referred as immunoglobulin A (IgA), immunoglobulin D (IgD) immunoglobulin E (IgE), immunoglobulin G (IgG) and immunoglobulin M (IgM) respectively.