'De novo' sequencing of Atlantic cod vitellogenin tryptic peptides by matrix-assisted laser desorption/ionization quadrupole time-of-flight tandem mass spectrometry: similarities with haddock vitellogenin

Vitellogenin is a protein produced by the liver of oviparous animals in response to circulating estrogens. The amino acid sequence of vitellogenin from Atlantic cod (Gadus morhua) has not yet been determined. In this study Atlantic cod vitellogenin was characterized using a 'bottom-up' mass spectrometric approach. Vitellogenin synthesis was induced 'in vivo' with beta-estradiol, and subjected to trypsin digestion for characterization by matrix-assisted laser desorption/ionization quadrupole time-of-flight tandem mass spectrometry. A peptide mass fingerprint was obtained and 'de novo' sequencing of the most abundant tryptic peptides was performed by low-energy collision-induced dissociation tandem mass spectrometry. As a result of these experiments, the sequences of various tryptic peptides have been elucidated. The database search has shown that Atlantic cod vitellogenin shares a series of common peptides with the two different known vitellogenin sequences of haddock, a closely related species. These findings allow us to propose that Atlantic cod might also co-express at least two distinct forms of vitellogenin.