Question

How can the terminal groups of amino acids be identified?

Answer 1

Identification of terminal groups of amino acids:

1. Proteins are polymers of different amino acids.
2. The distinctness of every protein is due to the sequence of amino acids linked.
3. The sequence of amino acids also determines its structure.
4. Hence, by determining the sequence of each amino acid via the process of protein degradation.
5. The protein has an N-terminal (amino end) and a C-terminal (carboxylic end)
6. The degradation process of amino acids can begin from N-terminal or C-terminal.

Edman degradation:

1. Edman degradation is the process of analysis of amino acids from the N-terminal.
2. It involves the treatment of the protein with phenyl isothiocyanate, which is also known as Edman's reagent.
3. The Edman's reagent helps to label the N-terminal amino acid under milk alkaline conditions which give rise to phenylthiocarbamide derivative.
4. Whereas when the conditions are changed to acidic, the labeled amino acid is cleaved from the parent chain and extracted using organic solvents.
5. The extraction process leads to the formation of a stable derivative known as phenylthiohydantoin (PTH derivative).
6. This PTH derivative can be easily recognized and analyzed using HPLC (High-performance liquid chromatography).
7. Hence, the counter receiver registers the N-terminal amino acid.
8. The process can be repeated several times through the N-terminal to determine the sequence of a protein.
9. Other reagents that can be used to label the amino acid are dansyl chloride, 1-fluoro-2,4- dinitrobenzene (FDNB), etc., which can be easily determined by dinitrophenyl derivatives.