14C dating of bone using γ-carboxyglutamic acid and α-carboxyglycine (aminomalonate)

Radiocarbon determinations have been obtained on gamma-carboxyglutamic acid [Gla] and alpha-carboxyglycine (aminomalonate) [Am] as well as acid- and base-hydrolyzed total amino acids isolated from a series of fossil bones. As far as we are aware, Am has not been reported previously in fossil bone and neither Gla nor Am C-14 values have been measured previously. Interest in Gla, an amino acid found in the non-collagen proteins osteocalcin and matrix Gla-protein (MGP), proceeds from the suggestion that it may be preferentially retained and more resistant to diagenetic contamination affecting C-14 values in bones exhibiting low and trace amounts of collagen. Our data do not support these suggestions. The suite of bones examined showed a general tendency for total amino acid and Gla concentrations to decrease in concert. Even for bones retaining significant amounts of collagen, Gla (and Am extracts) can yield C-14 values discordant with their expected age and with C-14 values obtained on total amino-acid fractions isolated from the same bone sample.