Edman degradation

Edman degradation is a method of sequencing amino acids in a peptide. It was developed by Pehr Edman, hence the name. The method labels and removes only the amino-terminal (N-terminal) amino acid of the protein, which allows the identification of the amino acid.

Process

The process of Edman degradation begins with the reaction of the N-terminal amino acid of the peptide with phenyl isothiocyanate under slightly alkaline conditions. This results in a phenylthiocarbamyl derivative. The peptide is then treated with anhydrous acid, which leads to the selective cleavage of the N-terminal amino acid as anilinothiazolinone derivative. The derivative can be easily identified by chromatography or electrophoresis. The remaining peptide, now shorter by one amino acid, can then undergo another round of degradation.

Limitations

While Edman degradation is a powerful tool for determining the N-terminal sequence of a peptide, it has several limitations. The method is relatively slow, with each cycle taking around 1 hour. It also requires a large amount of the peptide to be effective. Furthermore, the method can only reliably sequence up to 50 amino acids. For larger peptides, other methods such as mass spectrometry are more effective.

Applications

Despite its limitations, Edman degradation has found wide use in the field of biochemistry. It is commonly used to determine the primary structure of small proteins. It can also be used to identify proteins or to determine the boundaries of a protein domain.

See also

• Protein sequencing
• Mass spectrometry
• Pehr Edman