Optical resolution of phenylthiohydantoin-amino acids and identification of phenylthiohydantoin-D-amino acid residue of [D-Ala2]-methionine enkephalin by capillary electrophoresis

Abstract

We propose a system of protein sequence analysis with DL differentiation using capillary electrophoresis (CE). This system consists of a protein sequencer and a CE. After fractionation of phenylthiohydantoin (PTH)-amino acids from the protein sequencer, optical resolution for each PTH-amino acid is performed by CE using some chiral selectors such as digitonin, o-trimethyl-β-cyclodextrin (TM-β-CD) and others. In addition, optical resolution of all standard PTH-DL-amino acids including PTH-DL-carboxymethyl-Cys (CM-Cys) and cysteic acid (CYA) except for PTH-DL-Lys was successfully developed. The resolution of PTH-DL-Lys could not be reconfirmed due to low reproducibility and the impurities. As a model peptide, [D-Ala2]-methionine enkephalin (L-Tyr-D-Ala-Gly-L-Phe-L-Met), was used and the sequence with DL differentiation was completely determined.