An isotope (18O, 15N, and 2H) technique to investigate the metal ion interactions between the phosphoryl group and amino acid side chains by electrospray ionization mass spectrometry

Soy protein degradation drives diversity of amino-containing compounds via Bacillus subtilis natto fermentation

Food fermentation has been playing an important role in producing bioactive components (e.g., peptides), which exert many healthy effects. In this study, it was observed that natto possessed significantly higher angiotensin I-converting enzyme (ACE) inhibitory effect than soybean. Meanwhile, a total of 246 amino-containing compounds were identified via LC-Q-TOF-MS/MS, including amino acids, dipeptides, tripeptides, O-methyl-peptide, and biogenic amines, 187 of them were only detected in natto. Of the list, dipeptides, with ACE inhibitory abilities or potentials, were found to be the most significantly up-regulated class and positively correlated with significantly increased ACE inhibitory activity of natto. Moreover, dynamic profiling elucidated the increased dipeptides were generated from water soluble and insoluble protein via Bacillus subtilis natto fermentation. Taken together, this study enriches the chemical diversity of natto and provides an in-depth insight into the degradation mechanism of soy protein during natto fermentation, which can be extended to other functional foods.

Fragmentation of pentacoordinate spirobicyclic aminoacyl-phosphoranes (P-AAs) by electrospray ionization tandem mass spectrometry concerning P-O and P-N bond cleavage

The fragmentation pathways of both protonated and sodiated pentacoordinate spirobicyclic aminoacylphosphoranes (P-AAs) have been studied by electrospray ionization multi-stage mass spectrometry (ESI-MS(n)) in positive mode. The possible pathways and their mechanisms are elucidated through the combination of ESI-MS/MS, isotope ((15)N and (2)H) labeling and high-resolution Fourier transform ion cyclotron resonance (FTICR)-MS/MS. The relative Gibbs free energies (ΔG) of the product ions and possible fragmentation pathways are estimated at the B3LYP/6-31 G(d) level of theory. The theoretical calculations show that both protonated and sodiated P-AAs would quickly fragment before Berry pseudorotation. For protonated P-AAs, they have different tendencies to P-O or P-N bond cleavage. For sodiated P-AAs, the P-N bond is easier to cleave and produces the tetracoordinated phosphorus ion H. These results to some extent may give a clue to the chemistry of the active sites of phosphoryl transfer enzymes and will enrich the gas-phase ESI-MS ion chemistry of pentacoordinate phosphoranes.