Edman Degradation: Identifying Amino Acid Sequences for Peptides

Edman degradation is a chemical method for sequentially determining the N-terminal amino acid sequence of peptides (such as proteins and peptide segments). This method was developed by Pehr Edman in the 1950s.

 

Working Principle

1. Reaction

The peptide or protein first reacts with the Edman reagent (phenyl isothiocyanate). This results in the N-terminal amino acid forming a stable cyclic thio-derived compound with the reagent.

 

2. Unchaining

Then, by heating or using acid, this cyclic compound breaks from the peptide chain, releasing a thio-derived compound corresponding to the N-terminal amino acid.

 

3. Analysis

This derivative is then identified through chromatography or other analytical techniques, determining the N-terminal amino acid of the original peptide or protein.

 

4. Repetition

For peptides or proteins with more than one amino acid, this process can be repeated in sequence, each time identifying the next amino acid, until the entire sequence is determined or the degradation efficiency decreases.

 

Advantages and Limitations

1. Advantages

(1) Edman degradation is a very specific method, very accurate in identifying the N-terminal amino acid.

(2) Compared with mass spectrometry, it does not require complex instruments.

 

2. Limitations

(1) The efficiency of Edman degradation decreases with increasing sequence length. Typically, the method is most suitable for identifying shorter peptides, such as those less than 50 amino acids.

(2) The method may not be as effective for certain difficult-to-handle amino acids or chemical modifications.

(3) In some applications, mass spectrometry may be faster and more sensitive.

 

Despite the increasing use of mass spectrometry in protein sequence analysis in recent years, Edman degradation remains an important tool, especially for certain specific research questions or applications.