On the origin of terrestrial homochirality for nucleosides and amino acids
On the origin of terrestrial homochirality for nucleosides and amino acids
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DOI：
10.1073/pnas.0904350106
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发表时间：
2009-06-09
影响因子：
11.1
通讯作者：
Cheng, Zhan-Ling
中科院分区：
文献类型：
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作者：
Breslow, Ronald;Cheng, Zhan-Ling
在地球上出现生命之前，重要的是氨基酸的构建单元必须以称为L构型的优势手性存在，而RNA的核糖则主要以D构型存在。由于普通的化学过程会以相等的L和D量产生它们，因此长期以来，所需的选择性如何产生一直是一个谜。碳质陨石，如1969年降落在澳大利亚的默奇森陨石，带来了一些不寻常的氨基酸，甲基取代了它们的α氢。它们不能外消旋化，并且具有小的但真实的过量的L构型。我们已经证明，他们可以参与合成正常的L氨基酸在可信的益生元条件下。我们和其他人表明，由于纯L型的溶解度高于更稳定的DL外消旋化合物晶体，因此小的偏好可以放大到具有非常高的L氨基酸优势的溶液中。在这里，我们表明，这种溶解度为基础的放大小过量的三个D核苷，尿苷，腺苷，和胞苷，也可以发生，形成非常高的D优势的解决方案，在可信的益生元条件下。鸟苷结晶为聚集体，并不以这种方式放大。然而，在益生元条件下，它可能是由放大的腺苷或胞苷水解的纯手性D核糖形成的。
Before life could start on earth, it was important that the amino acid building blocks be present in a predominant handedness called the L configuration and that the ribose of RNA be predominantly in the D configuration. Because ordinary chemical processes would produce them in equal L and D amounts, it has long been a puzzle how the needed selectivities could have arisen. Carbonaceous chondrites such as the Murchison meteorite, which landed in Australia in 1969, brought some unusual amino acids with a methyl group replacing their alpha hydrogen. They cannot racemize and have a small but real excess of those with the L configuration. We have shown that they can partake in a synthesis of normal L amino acids under credible prebiotic conditions. We and others showed that small preferences can be amplified into solutions with very high dominance of the L amino acids because of the higher solubility of the pure L form than of the more stable DL racemic compound crystal. Here, we show that such solubility-based amplification of small excesses of three D nucleosides, uridine, adenosine, and cytidine, can also occur to form solutions with very high D dominance under credible prebiotic conditions. Guanosine crystallizes as a conglomerate and does not amplify in this way. However, under prebiotic conditions it could have been formed from homochiral D ribose from the hydrolysis of amplified adenosine or cytidine.