FIGURE 3.

A, schematic representation of the reduction, alkylation, and enzymatic digestion protocol applied to a cyclotide fraction from HPLC purification. Combined digestion using trypsin and endoproteinase Glu-C resulted in three fragments: A, B, and C. B, MS/MS spectra were collected for fragments A and B allowing assignment of their peptide sequence. Fragment C was too small to allow MS/MS sequencing. A single digestion strategy using only endoproteinase Glu-C revealed the full-length peptide sequence.