A micromethod for the determination of carboxyl-terminal amino acids of peptides and proteins: phenylisothiocyanate reaction with hydrazinolysates.

Proteins and peptides are digested with anhydrous hydrazine and the free amino acids, released from their carboxyl termini, are analyzed by reverse-phase chromatography as phenylthiocarbamyl (PTC) derivatives. Most of the potentially interfering hydrazides are removed due to the insolubility of their derivatives in the solution used for dissolving the phenylthiocarbamyl-amino acids. This methodology can be used to analyze peptides and proteins in quantities smaller than 100 pmol. The method is here employed for the screening of carboxyl termini in peptide fractions originating from an HPLC chromatogram.