Evidence for γ-carboxylation of glutamic acid residues in the Gla domain. Reconstructed mass spectra of peptides spanning the Gla domain: (A) Lc1-21 and (B) Lc22-36. Total masses of these peptides are consistent with the presence of Gla residues in them. Partially decarboxylated peptides with masses corresponding to successive loss of up to 4 and 3 carbon dioxide molecules (∼44 mass units), respectively, can also be identified.