Fig. 2. The pro-invasive factor is a β-casein-derived peptide. (A) Differential MS-spectra of CM prepared on collagen with (CM^CollListeria/TSB) or without (CM^CollTSB) bacteria. RP-HPLC-MS analysis of CM^CollListeria/TSB revealed doubly (⁺2) and triply (⁺3) charged ions of 443.21, 807.87 and 538.92 mass/charge, absent in CM^CollTSB. Vertical lines represent relative intensity (%) of ions. Numerical values indicate mass/charge of reference ions. (B) Identification of the doubly charged ion 807.87 by fragmentation analysis. The identified sequence is represented by the b-ion series HKEMPFPKYPVEP. Annotations of y-ions, internal fragment ions and ions with loss of methane sulfenic acid are omitted. Vertical lines represent ions relative intensity (%). Numerical values indicate mass/charge of reference ions.