Levy M, Miller S L
Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, CA 92093-0506, USA.
Proc Natl Acad Sci U S A. 1998 Jul 7;95(14):7933-8. doi: 10.1073/pnas.95.14.7933.
High-temperature origin-of-life theories require that the components of the first genetic material are stable. We therefore have measured the half-lives for the decomposition of the nucleobases. They have been found to be short on the geologic time scale. At 100 degreesC, the growth temperatures of the hyperthermophiles, the half-lives are too short to allow for the adequate accumulation of these compounds (t1/2 for A and G approximately 1 yr; U = 12 yr; C = 19 days). Therefore, unless the origin of life took place extremely rapidly (<100 yr), we conclude that a high-temperature origin of life may be possible, but it cannot involve adenine, uracil, guanine, or cytosine. The rates of hydrolysis at 100 degreesC also suggest that an ocean-boiling asteroid impact would reset the prebiotic clock, requiring prebiotic synthetic processes to begin again. At 0 degreesC, A, U, G, and T appear to be sufficiently stable (t1/2 >/= 10(6) yr) to be involved in a low-temperature origin of life. However, the lack of stability of cytosine at 0 degreesC (t1/2 = 17, 000 yr) raises the possibility that the GC base pair may not have been used in the first genetic material unless life arose quickly (<10(6) yr) after a sterilization event. A two-letter code or an alternative base pair may have been used instead.
高温生命起源理论要求第一种遗传物质的组成部分是稳定的。因此，我们测定了核碱基分解的半衰期。结果发现，在地质时间尺度上，它们的半衰期很短。在100摄氏度（嗜热超嗜热菌的生长温度）时，半衰期太短，无法使这些化合物充分积累（腺嘌呤和鸟嘌呤的半衰期约为1年；尿嘧啶为12年；胞嘧啶为19天）。因此，除非生命起源极其迅速（<100年），我们得出结论，高温生命起源是有可能的，但它不可能涉及腺嘌呤、尿嘧啶、鸟嘌呤或胞嘧啶。100摄氏度时的水解速率还表明，小行星撞击导致海洋沸腾会重置前生物时钟，需要前生物合成过程重新开始。在0摄氏度时，腺嘌呤、尿嘧啶、鸟嘌呤和胸腺嘧啶似乎足够稳定（半衰期≥10^6年），可以参与低温生命起源。然而，胞嘧啶在0摄氏度时缺乏稳定性（半衰期为17000年），这增加了一种可能性，即除非在灭菌事件后生命迅速出现（<10^6年），否则GC碱基对可能并未用于第一种遗传物质。可能使用的是双字母编码或替代碱基对。
