[Identification of the N-terminal peptide of bovine tryptophanyl-tRNA-synthetase]

By means of covalent chromatography on thiopropyl-sepharose 6B the N-terminal, as well as other tryptic cysteine-containing peptides of the bovine tryptophanyl-tRNA-synthetase (EC 6.1.1.2) were purified and characterized, their structures being determined by a combination of plasma desorption mass spectrometry and peptide sequencing. In total, six different peptides containing seven cysteine residues were analysed. The N-terminal amino acid (presumably, alanine) was shown to be acetylated in the nature enzyme amino acid sequences of some cysteine-containing peptides proved to differ from those deduced from the cDNA structure, thus indicating the presence of the enzyme's isoforms. The purification does not affect the peptides' sulfhydryl groups. The number of cysteine residues in the peptides could be determined with a high accuracy by measuring their masses before and after alkylation with 4-vinylpyridine.