Racemization rates of amino acids for dating ancient samples
Racemization rates of amino acids for dating ancient samples
复制标题
DOI：
10.1007/bf00805796
复制
发表时间：
1993-02
期刊：
影响因子：
3.5
通讯作者：
G. Lubec;B. Lubec
中科院分区：
文献类型：
--
作者：
G. Lubec;B. Lubec
Goodfriend建议使用天冬氨酸的快速外消旋化来测定年代（Goodfriend，1992）。我们认为，作为任何氨基酸定年系统的应用，该系统也有其价值和局限性。我们对一系列古代头发样品进行了氨基酸外消旋化，并根据这些观察和实验数据对影响氨基酸外消旋化的许多因素进行了评论，使这种类型的测年方法对单个样品不可靠，但对一组样品有用。然而，我们有数据支持Goodfriend的工作。一份被证实的文件价值一千美元。我们研究了来自最年长的样本的头发的结构稳定性，一个前王朝的人，公元前3200年到埃及木乃伊，第18 - 25王朝到科普特人（埃及基督徒），来自8- 10世纪的坟墓（Lubec等人，1987年）。在x射线衍射和红外研究方面的头发样品的结构稳定性不变。使用参与结构蛋白构象测定的氨基酸（脯氨酸和羟脯氨酸）评价了在此长时间内必须发生的外消旋化;检查了其外消旋化（即D/L比）和异构化（即顺-反羟脯氨酸）。最近的头发样本作为对照。通过高压液相色谱法进行分析（Kampel等人，1990）和由GC/MS控制的定量荧光薄层色谱法（Lubec等人，1992).图中给出的结果显示，发现最古老样品的外消旋化率（D/L脯氨酸）在木乃伊的范围内。不用说，这一维度的重叠将限制氨基酸测年的使用。十个科普特人中有两个的数值接近木乃伊的数据。反式顺式4羟脯氨酸的异构化，但是，明确地分开了三个不同的时期。我们是否可以假设外消旋化和异构化有两种不同的化学机制？前王朝的人埋在炎热干燥的沙子，保存了他的身体约5200年和外消旋值类似的木乃伊前，
Goodfriend proposes the use of rapid racemization of aspartic acid for dating (Goodfriend, 1992). We think that as the application of any amino acid dating system also this system has its values and limitations. We applied amino acid racemization on a series of ancient hair samples and would like to comment on the many factors influencing amino acid racemization based upon these observations and experimental data, making this type of dating unreliable for individual samples, though useful for a group of samples. We have, however, data in support of Goodfriend's work. And a confirmed paper is worth thousand unsupported. We studied structural stability of hair from the eldest samples, a predynastic man, 3200 years BC to Egyptian mummies 18th-25th dynasty to copts (Egyptian christians) from 8-10th century graves (Lubec et al., 1987). Structural stabilities of hair samples were unchanged in terms of x ray diffraction and infrared studies. Racemization that must have been taken place over this long period was evaluated using amino acids involved in the determination of the conformation of structural proteins: proline and hydroxyproline; their racemization ie D/L ratios and isomerization ie cis-trans hydroxyprolines were examined. Recent hair samples served as controls. The analyses were carried out by high pressure liquid chromatography (Kampel et al., 1990) and quantitative fluorescence thinlayer chromatography controlled by GC/MS (Lubec et al., 1992).The results are given in the figure showing that the oldest sample's racemization rate (D/L proline) was found in the range of mummies. Needless to say that an overlap of this dimension would limit the use of amino acid dating. Two out of the ten copts examined showed values close to the mummies' data. The isomerization of trans to cis 4 hydroxyproline, however, clearly separated the three different periods. Can we assume that racemization and isomerization have two different chemical underlying mechanisms? The predynastic man buried in the hot dry sand that preserved his body for approx 5200 years and racemization values resembling those of mummies pre-