Complete amino acid sequence of the light chain of human blood coagulation factor X: evidence for identification of residue 63 as .beta.-hydroxyaspartic acid

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Abstract
The complete amino acid sequence of L chain of human blood coagulation factor X was determined by automated Edman degradation of peptides isolated from chemical and enzymatic digests of the carboxymethylated L chain. The protien consists of 139 amino acid residues, which include 11 residues of .gamma.-carboxyglutamic acid. The first 100 residues of the human factor XLC chain exhibit .apprx. 80% homology when compared to the amino-terminal sequence of bovine factor XL chain. This homology decreases to .apprx. 50% in the remaining 39 residues of the carboxyl-terminal regin of the protein. Proton NMR spectroscopy and mass spectrometry analyses of isolated residue 63 identified this residue as L-erythro-.beta.-hydroyaspartic acid, a hitherto unrecognized amino acid in proteins. Evidence is also presented for the presence of this residue in the corresponding regions of the L chains of bovine factor X and bovine protein C. The biological function of .beta.-hydroxyaspartic acid in these proteins is unknown.

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