Carbon and nitrogen isotope fractionations of collagen by chemical treatment : mainly by XAD-2 treatment


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  • 化学処理による骨コラーゲンの炭素・窒素同位体比の変化 : 主にXAD-2樹脂処理について

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XAD-2 rasin is considered a good material to separate quantiatively polar amino acids from less polar fulvic and humic acids, which are predominant sources of error in ^<14>C and stable isotope analysis on collagen of fossil bone. To evaluate if XAD-2 treatment affects carbon and nitrogen isotope values, Minami (1999) measured δ^<13>C and δ^<15>N on several extracted fractions of collagens from modern bovine Achilles heel tendons made of Sigma Chemical and Nacalai Tesque. There were about +1.0‰ difference in δ^<13>C and about -0.1‰ in δ^<15>N between hydrolyzed collagen and XAD-treated collagen hydrolysates from modern collagen standards. On the other hand, the carbon and nitrogen isotope fractionations were about -0.6‰ and +0.3‰ in δ^<15>N, respectively, on animal fossil bones collected from collected from the Awazu submarine archeological site in this study. The C/N ratios, δ^<13>C and δ^<15>N values of extracted fractions : decalcified, hydrolyzed and XAD-treated hydrolysate fractions, vary as chemical extraction proceeded. The change of the isotope values, which differ between fossils and modern collagens, might be caused by purification of collagen, decomposition of a part of collagen, and combined changes in amino acid composition in collagen. The XAD-treatment affected amino acid compositions on both fossils and modern collagen standards. Since there was no difference in both δ^<13>C and δ^<15>N values by XAD-2 treatment on amino acid standards (Minami, 1999), the isotope fractionation with XAD-2 resin on the collagens can not be due to the total isotope variation of individual amino acids, but be due to the change of amino acid compositions. We need to further study the effect of chemical treatment with HCl on carbon and nitrogen isotope ratios of collagen with XAD-2 resin.



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