Fig. 3

De novo sequencing of compound 3 from fraction F11 by LC-ESI-QTOF MS/MS after reduction, alkylation and protease digestion. a LC-ESI-QTOF MS of compound 3 after reduction and alkylation. This allows the calculation of the number of disulfide bridges. b LC-ESI-QTOF MS of compound 3 after reduction, alkylation and V8 protease digestion. Inset illustrates the MS of m/z 1509.6704 [1+]. c LC-ESI-QTOF MS/MS of precursor ion m/z 1509.6704. The peptide sequence RWLGCAKTCTEE is derived by de novo peptide sequencing. Peaks corresponding to the y and b ions from this peptide are labeled on the spectrum