Primary Structure of Proteins
The arrangement of amino acids residues along the peptide chain called the primary structure of proteins. It can also determine the number of amino acids on peptide chain. It can also detect whether the peptide chain Is open, cyclic or branched. The primary structure of several peptide is regulated by the respective genes on specific chromosome. The numbering of amino acids in peptide chain are start from those amino acid which do not contain –NH2 group.
There are 20 standard amino acids which are used for the formation of peptide molecule; they linked with each other by peptide linkages. The formation of peptide from individual amino acid can be compared with the English alphabets. These peptide are differ from each other in number and the sequence of amino acid a in their respective molecule. In some peptide molecule the amino acid are very few, but in some peptide molecule these can be more then hundred. If we substitute even one amino acid in the peptide molecule it result the dramatic change in its properties.
The primary structure of large number of polypeptide have been illuminate the number of amino acids residues in some of these is given bellow.
Insulin (51), Ribonuclease (124), α chain of hemoglobin (141), β chain of hemoglobin (164), proteins of the tobacco virus (158), oxytocin (8), vasopressin (8), ACTH (39), angiotensin- 1 (10), angiotensin- 2 (8), angiotensin- 3 (7), glucagon (29), cacitonin (32) .
Insulin of beef origin is the proteins whose primary structure was discovered first at all. This was done by Sanger in 1953 who was awarded noble prize for chemistry in 1958. Now including human several other species insulin primary structure is well known.
Human insulin is consisting of two chain, chain A and chain B. chain A contain 21 amino acids and chain B contain 30 amino acid. These two chains are linked with each other at two sites by –S-S- linkages. The insulin of pork and whale resemble with each other, and both are differ with human insulin with respect to one amino acid. The beef insulin differs with respect to three amino acid whereas sheep insulin is differing from the human insulin with respect to four amino acids.
As mentioned in above paragraph Sanger discovered the primary structure of insulin. He had devalop FDNB for labeling the amino terminal amino acid. These are followed by use of other such reagents namely dansylchlorid and dabsyl chlorid which proved better then the originally used FDNB. However Edman’s method made this procedure more easy.