Figure 1

The scheme for Met-peptide enrichment. Reduced Met-peptides are labeled by the iodoacetyl-PEG2-biotin reagent under acidic conditions, whereas the oxidized Met-peptides are not. The labeled peptides are then captured and purified with streptavidin-Sepharose beads. After reduction by DTT, the captured Met-peptides are released from the beads and analyzed by LC-MS/MS.