Effects of glutamine deamidation on the oxygen isotope compositions of bone collagen
Abstract
The oxygen (O) isotope composition of mammalian collagen has the potential to provide information about the drinking water and hence geographic location and climate during the life of modern and ancient animals. An accurate and reproducible O-isotope analysis of collagen, however, has been elusive. Here, the O-isotope compositions of collagen from cortical bone of four megaherbivores were compared using two extraction procedures: the traditional Longin (HCl) method and the less commonly employed EDTA method. Preservation of O-isotope compositions was evaluated by measuring collagen peptide-chain masses, specifically the glutamine deamidation level (GDL). The EDTA method yielded collagen with a GDL of 1 – characteristic of unaltered collagen – and reproducible O-isotope results (±0.8‰). Much lower GDL values (0.2-0.95) and poorer reproducibility (±1.6‰) was obtained for the Longin method. This method uses strong acids to demineralize bioapatite releasing collagen, catalyzing reactions such as glutamine deamidation leading to O-isotope exchange with reagents, and should be avoided.