A mass-spectrometric method for the estimation of the ratio of γ-carboxyglutamic acid to glutamic acid at specific sites in proteins. Application to the N-terminal region of bovine prothrombin

Abstract

When a polypeptide containing gamma-carboxyglutamic acid is decarboxylated in 2H2O, residue of (gamma gamma-2H2)glutamic acid are formed. Subsequent proteolytic digestion produces peptides which contain at each site 2H2-substituted and unsubstituted glutamic acid in the same ratio as existed for gramma-carboxy-substitution. The peptides may be identified and this ratio determined by combined gas chromatography–mass spectrometry. We also discuss decarboxylation in 3H2O followed by amino-acid analysis and Edman degradation.