[U-12] CO環境の生命惑星化学

[U12-P05] COとアンモニアから選択的アミノ酸が合成される環境条件の探索

*浅倉 裕太¹、Fong Andy²、藏 暁鳳¹、毛利 晃大¹、上野 雄一郎^1,3,4 (1.東京科学大学、2.マサチューセッツ工科大学、3.東京科学大学地球生命研究所、4.海洋研究開発機構)

キーワード：前生物化学、アミノ酸の選択性、紫外線照射実験

Amino acids are essential building blocks of life, and their prebiotic synthesis is crucial for the origin of life. However, the selectivity of amino acids synthesized from various prebiotic reactions are largely unknown despite life using only 20 α-amino acids, which are homochiral. It is hypothesized in literature that amino acids form more efficiently under reducing atmospheres [1]. For example, amino acids have been successfully synthesized from CO-rich atmospheres in the laboratory in the presence of nitrous oxide [2]. Herein, we explore the environmental conditions which favor synthesis of selective amino acid from UV photochemistry of CO and NH₃ in water. Specifically, we aim to identify (1) conditions that produce a high concentration of amino acids and (2) conditions that favor the synthesis of α-amino acids and an enantiomeric excess of L-amino acids. In our experiment, CO + NH₃ + H₂O were photolyzed with 10 different minerals. The results showed that amino acid production was particularly enhanced when adding Ca(OH)₂. Furthermore, when adding metal sulfides (FeS, NiS, CuS and ZnS), the production of α-amino acids (glycine, alanine, serine, and aspartic acid) was selectively enhanced with respect to the control run without any minerals. In addition, we conducted experiments in which the pH was buffered to acidic (pH = 2) and basic (pH = 12) conditions by adding adjusted amounts of HCl, NaOH, and NaCl. The systematic analysis revealed that amino acid production was an order of magnitude higher for alkaline condition irrespective of the presence of additives. In contrast, under acidic conditions, significant L-excesses of alanine, serine, and glutamic acid were observed regardless of the additive used. This may suggest that amino acids were synthesized via more than two different pathways, one of which may possibly contribute enantiomeric excess and proceed in a particularly low pH environment.

[1] Schlesinger G., and Miller S. (1983) Prebiotic synthesis in atmospheres containing CH₄, CO and CO₂. Journal of molecular evolution, 19: 376-382.
[2] Zang X., Ueno Y., and Kitadai N. (2022) Photochemical Synthesis of Ammonia and Amino Acids from Nitrous Oxide. Astrobiology, 22: 387-398.