Ist eine Revision der Aminosäurendatierung möglich?

Liegezeitschätzungen von Skelettfunden mittels der Aminosäurendatierung (AAR) sind nach Fehldatierungen umstritten. Ziel der Arbeit war die Prüfung möglicher Revisionsansätze. Zugrunde lag die Hypothese, dass die AAR nur verwertbare Ergebnisse liefert, wenn definierte Proteinfraktionen untersucht werden. An künstlich und natürlich gealtertem Kollagen wurden Präparationsverfahren entwickelt, und deren Nutzbarkeit für die AAR untersucht. Als Hauptproblem wurde der unvorhersagbare Verlust von Kollagenfragmenten mit hochrazemisierten Aminosäuren an die Umwelt im Zuge der Proteindegradation identifiziert. Solche Fragmente fanden sich nach CNBr-Spaltung des Kollagens unter den kleinsten, hier nicht weiter aufzureinigenden Peptiden. Sollten diese Kollagenbruchstücke als „Liegezeit-Uhr“ im Knochen erhalten bleiben, stellt die auf niedermolekulare Peptide zielende Präparation die letzte methodische Chance für eine erfolgreiche Revision der AAR dar. Die AAR wurde daher weiter problematisiert statt revidiert. Die erhobenen Daten sind dennoch von praktischer Relevanz, da jüngste "erfolgreiche" Aminosäurendatierungen auf dieser Grundlage kritisch diskutiert werden können

Is amino acid racemization a useful tool for screening for ancient DNA in bone?

Many rare and valuable ancient specimens now carry the scars of ancient DNA research, as questions of population genetics and phylogeography require larger sample sets. This fuels the demand for reliable techniques to screen for DNA preservation prior to destructive sampling. Only one such technique has been widely adopted: the extent of aspartic acid racemization (AAR). The kinetics of AAR are believed to be similar to the rate of DNA depurination and therefore a good measure of the likelihood of DNA survival. Moreover, AAR analysis is only minimally destructive. We report the first comprehensive test of AAR using 91 bone and teeth samples from temperate and high-latitude sites that were analysed for DNA. While the AAR range of all specimens was low (0.02-0.17), no correlation was found between the extent of AAR and DNA amplification success. Additional heating experiments and surveys of the literature indicated that d/l Asx is low in bones until almost all the collagen is lost. This is because aspartic acid is retained in the bone within the constrained environment of the collagen triple helix, where it cannot racemize for steric reasons. Only if the helix denatures to soluble gelatin can Asx racemize readily, but this soluble gelatine is readily lost in most burial environments. We conclude that Asx d/l is not a useful screening technique for ancient DNA from bone

Is amino acid racemization a useful tool for screening for ancient DNA in bone?

Many rare and valuable ancient specimens now carry the scars of ancient DNA research, as questions of population genetics and phylogeography require larger sample sets. This fuels the demand for reliable techniques to screen for DNA preservation prior to destructive sampling. Only one such technique has been widely adopted: the extent of aspartic acid racemization (AAR). The kinetics of AAR are believed to be similar to the rate of DNA depurination and therefore a good measure of the likelihood of DNA survival. Moreover, AAR analysis is only minimally destructive. We report the first comprehensive test of AAR using 91 bone and teeth samples from temperate and high-latitude sites that were analysed for DNA. While the AAR range of all specimens was low (0.02 -0.17), no correlation was found between the extent of AAR and DNA amplification success. Additional heating experiments and surveys of the literature indicated that D/L Asx is low in bones until almost all the collagen is lost. This is because aspartic acid is retained in the bone within the constrained environment of the collagen triple helix, where it cannot racemize for steric reasons. Only if the helix denatures to soluble gelatin can Asx racemize readily, but this soluble gelatine is readily lost in most burial environments. We conclude that Asx D/L is not a useful screening technique for ancient DNA from bone