1. What Is a Protein Sequencer?

A protein sequencer automates Edman degradation, a method developed by Pehr Victor Edman in 1950. The reaction scheme is as follows.

(1) Coupling Reaction

Under basic conditions, phenyl isothiocyanate (PITC) is coupled to the N-terminal amino group of the isolated and purified sample protein (including peptides).

(2) Cleavage Reaction

Under acidic conditions, the PITC-coupled N-terminal amino acid is cleaved and extracted into the organic phase as an anilinothiazolinone (ATZ) derivative.

(3) Conversion Reaction

The organic solvent is evaporated, and the extracted ATZ derivative is converted in acidic aqueous solution to a stable derivative known as a phenylthiohydantoin (PTH) amino acid.

The PPSQ-50 Series system determines the amino acid sequence by sequentially cleaving amino acids, such as PTH-amino acids, from the N-terminus of a protein via Edman degradation and analyzing them by HPLC.
As shown in the figure on the right, one complete sequence of steps—from Edman degradation to PTH-amino acid analysis by HPLC—constitutes one cycle. By repeating this cycle and assembling the resulting PTH-amino acids in order, the N-terminal amino acid sequence of a protein or peptide can be accurately and reliably determined. The amino acid sequence of proteins not registered in any database can also be determined. Applications extend beyond basic research to include the analysis of antibody-based therapeutics, as well as proteins and peptides in food products, among many others.