The primary structure of thioredoxin from Chromatium vinosum determined by high-performance tandem mass spectrometry

The primary structure of thioredoxin, a redox protein isolated from Chromatium vinosum, was determined by high-performance tandem mass spectrometry, which permitted sequencing of the 14 peptides (ranging in length from 2 to 18 amino acids) generated by digestion with trypsin and of several peptides produced by Staphylococcus aureus protease. The mass spectrometrically determined molecular weights of the peptides from the latter digest were used to properly align the tryptic peptides, which could also be accomplished on the basis of the considerable homology with Escherichia coli thioredoxin. Finally, the molecular weight of the Chromatium thioredoxin was determined by mass spectrometry and found to be 11,748.0, in good agreement with 11,750.2 calculated for the proposed sequence. Although it was difficult to establish by mass spectrometry, five leucines and three isoleucines could be identified, leaving only eight undifferentiated.