beta-Hydroxyaspartic acid in vitamin K-dependent protein C.

Abstract
The L chain of protein C, an anticoagulant plasma protein, apparently contains an unusual amino acid. To determine the structure of this amino acid a heptapeptide, CMCys-Ile-X-Gly-Leu-Gly-Gly (residues 69-75 in the L chain), was isolated from enzymatic digests of the L chain. According to automatic Edman sequence analysis, 1H NMR spectroscopy and mass spectrometry, the heptapeptide had .beta.-hydroxyaspartic acid in its 3rd position, which corresponds to position 71 in the L chain of protein C. Analysis of acid and aminopeptidase M hydrolysates of the heptapeptide showed the .beta.-hydroxyaspartic acid to be the erythro form. Acid hydrolysis of protein C released .apprxeq. 1 mol of .beta.-hydroxyaspartic acid/mol of protein. The function of this amino acid, which was not found previously in proteins, is unknown.