National Aeronautics and Space Administration Goddard Space Flight Center and The Goddard Center for Astrobiology, Greenbelt, MD 20771, USA.
Proc Natl Acad Sci U S A. 2011 Aug 23;108(34):13995-8. doi: 10.1073/pnas.1106493108. Epub 2011 Aug 11.
All terrestrial organisms depend on nucleic acids (RNA and DNA), which use pyrimidine and purine nucleobases to encode genetic information. Carbon-rich meteorites may have been important sources of organic compounds required for the emergence of life on the early Earth; however, the origin and formation of nucleobases in meteorites has been debated for over 50 y. So far, the few nucleobases reported in meteorites are biologically common and lacked the structural diversity typical of other indigenous meteoritic organics. Here, we investigated the abundance and distribution of nucleobases and nucleobase analogs in formic acid extracts of 12 different meteorites by liquid chromatography-mass spectrometry. The Murchison and Lonewolf Nunataks 94102 meteorites contained a diverse suite of nucleobases, which included three unusual and terrestrially rare nucleobase analogs: purine, 2,6-diaminopurine, and 6,8-diaminopurine. In a parallel experiment, we found an identical suite of nucleobases and nucleobase analogs generated in reactions of ammonium cyanide. Additionally, these nucleobase analogs were not detected above our parts-per-billion detection limits in any of the procedural blanks, control samples, a terrestrial soil sample, and an Antarctic ice sample. Our results demonstrate that the purines detected in meteorites are consistent with products of ammonium cyanide chemistry, which provides a plausible mechanism for their synthesis in the asteroid parent bodies, and strongly supports an extraterrestrial origin. The discovery of new nucleobase analogs in meteorites also expands the prebiotic molecular inventory available for constructing the first genetic molecules.
所有陆地生物都依赖于核酸（RNA 和 DNA），核酸使用嘧啶和嘌呤核苷来编码遗传信息。富含碳的陨石可能是早期地球上生命出现所需有机化合物的重要来源；然而，陨石中核苷酸碱基的起源和形成已经争论了 50 多年。到目前为止，在陨石中报道的少数核苷酸碱基在生物学上很常见，并且缺乏其他本土陨石有机物所具有的结构多样性。在这里，我们通过液相色谱-质谱法研究了 12 种不同陨石甲酸提取物中核苷酸碱基和核苷酸碱基类似物的丰度和分布。默奇森和孤狼 Nunataks 94102 陨石中含有一套种类繁多的核苷酸碱基，其中包括三种不常见且在地球上很少见的核苷酸碱基类似物：嘌呤、2,6-二氨基嘌呤和 6,8-二氨基嘌呤。在平行实验中，我们在氨氰化物反应中发现了一组相同的核苷酸碱基和核苷酸碱基类似物。此外，在任何程序空白、对照样品、陆地土壤样品和南极冰样品中，这些核苷酸碱基类似物的含量都未超过我们十亿分之几的检测限。我们的结果表明，陨石中检测到的嘌呤与氨氰化物化学产物一致，这为它们在小行星母体中的合成提供了一个合理的机制，并强烈支持其为外星起源。陨石中发现的新核苷酸碱基类似物也扩展了用于构建第一个遗传分子的前生物分子库存。
