Counting Integral Numbers of γ-Carboxyglutamic Acids Per Peptide Chain Using Capillary Electrophoresis

A method for counting the number of γ-carboxyglutamic acid (Gla) residues in peptides is presented. The product mixture generated by partial decarboxylation of a peptide containing multiple Gla residues is separated by capillary electrophoresis. A mixture derived from a peptide containing n Gla residues produces an electropherogram characterized by n + 1 peak groups. For a given peptide, a linear relationship (r2 > 0.99) is observed between the average electrophoretic mobility of each peak group and the representative number of Gla residues contained by that group. Resolution of peptide isomers is also obtained, permitting studies of the extent and sequence-specificity of decarboxylation.