Poinar H N, Höss M, Bada J L, Pääbo S
University of Munich, Germany.
Science. 1996 May 10;272(5263):864-6. doi: 10.1126/science.272.5263.864.
The extent of racemization of aspartic acid, alanine, and leucine provides criteria for assessing whether ancient tissue samples contain endogenous DNA. In samples in which the D/L ratio of aspartic acid exceeds 0.08, ancient DNA sequences could not be retrieved. Paleontological finds from which DNA sequences purportedly millions of years old have been reported show extensive racemization, and the amino acids present are mainly contaminates. An exception is the amino acids in some insects preserved in amber.
天冬氨酸、丙氨酸和亮氨酸的消旋程度为评估古代组织样本是否含有内源性DNA提供了标准。在天冬氨酸的D/L比率超过0.08的样本中，无法检索到古代DNA序列。据报道从中获得了据称有数百万年历史的DNA序列的古生物学发现显示出广泛的消旋现象，且所存在的氨基酸主要是污染物。一个例外是保存在琥珀中的一些昆虫体内的氨基酸。
