IDENTIFICATION OF THE N-TERMINAL PEPTIDE OF THE BOVINE TRYPTOPHANYL-TRANSFER-RNA-SYNTHETASE

By means of covalent chromatography on thiopropyl-sepharose 6B the N-t erminal, as well as other tryptic cysteine-containing peptides of the bovine tryptophanyl-tRNA-synthetase (EC 6.1.1.2) were purified and cha racterized, their structures being determined by a combination of plas ma desorption mass spectrometry and peptide sequencing. In total, six defferent peptides containing seven cysteine residues were analysed. T he N-terminal amino acid (presumably, alanine) was shown to be acetyla ted in the nature enzyme amino acid sequences of some cysteine-contain ing peptides proved to differ from those deduced from the cDNA structu re, thus indicating the presence of the enzyme's isoforms. The purific ation does not affect the peptides' sulfhydryl groups. The number of c ysteine residues in the peptides could be determined with a high accur acy by measuring their masses before and after alkylation with 4-vinyl pyridine.