Edman degradation chemistry

A major advance was devised by Pehr Edrnan (University of Lund, Sweden) that has become the standard method for N-terminal residue analysis. The Edman degradation is based on the chemistry shown in Figure 27.12. A peptide reacts with phenyl isothiocyanate to give a phenylthiocarbamoyl (PTC) derivative, as shown in the first step. This PTC derivative is then treated with an acid in an anhydrous medium (Edrnan used nitrornethane saturated with hydrogen chloride) to cleave the amide bond between the N-terminal anino acid and the remainder of the peptide. No other peptide bonds are cleaved in this step as amide bond hydrolysis requires water. When the PTC derivative is treated with acid in an anhydrous medium, the sulfur atom of the C=S unit acts as... 

Recently, Laursen realized the concept of a novel Peptide-Sequencer based on the chemistry of the Edman degradation, adapted to solid phase chemistry. The peptide under investigation is covalently linked to a resin packed into a column. The reactions are carried out by pumping the reagents and solvents through the column as required. This method appears to be particularly suitable for shorter peptides and may be regarded as an excellent supplement to the Sequencer based on Edman s design. 

The Edman degradation method for polypeptide sequence determination. The sequence is determined one amino acid at a time, starting from the amino-terminal end of the polypeptide. First the polypeptide is reacted with phenylisothiocyanate to form a polypeptidyl phenylthiocarbamyl derivative. Gentle hydrolysis releases the amino-terminal amino acid as a phenylthiohydantoin (PTH), which can be separated and detected spectrophoto-metrically. The remaining intact polypeptide, shortened by one amino acid, is then ready for further cycles of this procedure. A more sensitive reagent, dimethylaminoazobenzene isothiocyanate, can be used in place of phenylisothiocyanate. The chemistry is the same. 

Peptide 35 was synthesized using Fmoc chemistry with Rink amide resin. Deprotection and cleavage were performed by treatment with TFA/EDT/anisole (95 1.25 3.75) for 1.5 h, and the peptide was precipitated with the addition of ice-cold EtjO. The precipitate was dissolved in aq AcOH and purified by preparative RP-HPLC using 0.1% TFA in a H20/MeCN gradient. The purified peptide sequence was confirmed by Edman degradation sequence analysis. FAB-MS analysis gave [M + H]+ 2331.2 Da (calcd 2331.1 Da). 

Figure 5-2. Chemistry of the Edman degradation. In the Edman degradation, peptides undergo reaction with phenylisothiocyanate which generates a phenylthiocarbamylpeptide adduct. This adduct is cleaved to release the...

Edman, Pehr Victor (1916-1977), a pioneer in the field of peptide and protein chemistry. Already for his Ph.D he had isolated and purified angiotensin. In 1947, he accepted an associate professorship at the University of Lund (Sweden), and in 1957 Edman came to Melbourne as the first John Holt director of research at St. Vincent s School of Medical Research. In 1972, he moved to Germany, having been appointed Professor at the Max-Planck-Institute for Biochemistry at Martinsried. He is the inventor of an important method for protein structure determination, named the Edman degradation [F. J. Morgan, Edman, Pehr Victor (1916-1977), Austr. Diet. Biograph. 1996, Volume 14, pp. 78-79]. 

As everybody knows, a sequencing machine digests the amino acid chain starting at the N-terminus and it identifies the amino acid derivatives via a connected HPLC. A requirement is a free N-terminus. The Pierce Catalog, for example, describes the chemistry of the Edman degradation of peptides with phenylisothiocyanate. Baumann (1990) compares the effectiveness of different sequencing techniques. 

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