Figure 2.

Pepsin digestion of PE and mass spectrometry. The map of pepsin-generated peptides after H-D exchange illustrates the excellent coverage of peptides spanning the PE protein, including the active peptides within the PE precursor. The active peptides consist of (Met)enkephalin (M), M-Arg-Gly-Leu (O, octapeptide), (Leu)enkephalin (L), and M-Arg-Phe (H, heptapeptide). The pepsin-generated peptides shown in black lines were used for analyses of H-D exchange of intact PE and peptides derived from PE in Figures 3 and 4. The gray lines were observed in pepsin digests of PE, but were not used in deuteration maps of PE in Figures 3 and 4.