Every protein has a unique amino acid sequence. Identification of the amino acids present in the protein in order describes the primary structure of the protein. Instruments that automatically sequence the peptides and proteins are now available. The analysis is based on the degradation of the peptide one amino acid at a time and identifying the amino acid.
The degradation can start from the terminal amino group side or terminal carboxylic side.
N-terminal analysis: The N-terminal analysis is done by Edman Degradation. The peptide is treated with phenyl thiocyanate. The products are a thiohydantoin heterocycle containing N-terminal amino acid and a shortened peptide chain. Sanger developed the reagent 1-fluoro-2,4- dinitrobenzene (FDNB) for this purpose; other reagents used to label the amino-terminal residue, dansyl chloride and dabsyl chloride, yield derivatives that are more easily detectable than the dinitrophenyl derivatives.