Figure 6. Gla methylation eliminates neutral loss.

Equivalent amounts of FLEEL peptide and the Gla (γ)-containing peptide FLγEL were subjected to LC-MS before (a, b) or after (c, d) treatment with methanolic HCl. Almost all of the Glus and Glas were methylated (Me), as indicated by data-dependent analysis and consistent with the results obtained by HPLC (Fig. 5). The CID spectra show that cleavage at the gamma-glutamyl carbon occurs with unmethylated- but not methylated CO₂ (b, d).