Sequencing of Peptides The Edman Method

The actual sequencing of each peptide produced by specific cleavage of a protein is accomplished by repeated application of the Edman degradation. 

The sequence of a peptide containing 10 to 40 residues can be determined by this method in about 30 minutes using as httle as 10 picomoles of material, with the range being based on the amount of purified fragment and the complexity of the sequence. For example, proline is more difficult to sequence 

Chymotrypsin Cyanogen bromide Chymotrypsin Cyanogen bromide Cyanogen bromide Chymotrypsin 

Partial digestion was effected using chymotrypsin and cyanogen bromide. For clarity, only the original N-terminus and C-terminus of the complete peptide are shown. 

A solution of a peptide of unknown sequence was divided into two samples. One sample was treated with trypsin, and the other was treated with chymotrypsin. The smaller peptides obtained by trypsin treatment had the following sequences  

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