On the recovery of Cys-containing peptides during peptide mapping by HPLC. Tryptic peptides of Trp-tRNA synthetase of E.coli.

Conditions are presented for separating the major tryptic peptides of E.coli tryptophanyl-transfer RNA synthetase by reversed-phase liquid chromatography using a water-methanol gradient in the presence of 0.1% trifluoroacetic acid. Three of the peptides contain cysteine and are recovered in good yields if alkylated, but otherwise cannot be detected. A convenient post-digestion alkylation procedure is appropriate for use with small samples of protein which can be digested under reducing conditions. These results will be of interest for studies of the labeling of sulfhydryl groups in other proteins.