The N-terminal sequences of blood coagulation factor X1 and X2 light chains. Mass-spectrometric identification of twelve residues of γ-carboxyglutamic acid in their vitamin K-dependent domains

Abstract

Peptides (residues 1-42)(bovine prothrombin numbering) from bovine factors X1 and X2 were separately purified and digested before mass-spectrometric sequence assignment and identification of .gamma.-carboxyglutamic acid. Each N-terminal sequence was identical, and 12 residues of .gamma.-carboxyglutamic acid were unambiguously identified. Conclusive evidence for the N-terminal primary structure of bovine factor X was provided. Present knowledge was extended to show unambiguous assignment of .gamma.-carboxyglutamic acid residues, including a previously unreported residue of .gamma.-carboxyglutamic acid at position 40 in factor X1 and factor X2. The physical difference between factors X1 and X2 was not due to either different amino acid sequences or different .gamma.-carboxyglutamic acid contents of the N-terminal 42 residues.