J. Biol. Chem., Vol. 256, Issue 19, 9944-9950, 10, 1981
Gas chromatographic mass spectrometric sequence determination of osteocalcin, a gamma-carboxyglutamic acid-containing protein from chicken bone
SA Carr, PV Hauschka and K Biemann
The complete primary structure of osteocalcin, the gamma- carboxyglutamic
acid (Gla)-containing calcium-binding protein isolated from chicken bone
has been determined by gas chromatographic mass spectrometry. The method
involves decarboxylation of the dry, intact protein in a low pressure
atmosphere of DCl under conditions which quantitatively convert Gla into
gamma, gamma-dideuteroglutamic acid residues without resulting in peptide
bond cleavage. After partial enzymatic or acidic hydrolysis, the peptide
mixtures are converted (without isolation of individual peptides) to the N-
trifluorodideuteroethyl O-trimethylsilyl polyamino alcohols and analyzed by
gas chromatographic mass spectrometry. Peptide fragments containing former
Gla residues behave like Glu-containing peptides, but their mass spectra
are shifted upward by 2 mass units/Gla residue. Chicken osteocalcin
contains 50 amino acids, three of which are Gla. The structure is highly
homologous to the sequence of the corresponding protein isolated from
bovine bone, and the relative sequence locations of the Gla residues and
the disulfide bridge are conserved.