Edman degradation sequencing peptide fragments

The third peptide (see third column of Table II) was a large one, composed of approximately thirteen amino acid residues according to our analytical data. The only unique residue was tyrosine, and it is difficult to assign the position of this fragment in the amino acid sequence of pepsin. Such an assignment must await the results of Edman degradation on the fragment. 

Sequence information for the remaining fragments was obtained by Edman degradation (see Section 5.3.1 above) after isolation of the individual peptides using preparative HPLC - the chromatographic resolution being sufficient to allow this, and thus enabled the complete sequence to be determined. 

In theory, Edman degradations could sequence a peptide of any length. In practice, however, the repeated cycles of degradation cause some internal hydrolysis of the peptide, with loss of sample and accumulation of by-products. After about 30 cycles of degradation, further accurate analysis becomes impossible. A small peptide such as bradykinin can be completely determined by Edman degradation, but larger proteins must be broken into smaller fragments (Section 24-9E) before they can be completely sequenced. 

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