The Asuka (A)-12236 meteorite has recently been classified as a CM carbonaceous chondrite of petrologic type 3.0/2.9 and is among the most primitive CM meteorites studied to date. Here, we report the concentrations, relative distributions, and enantiomeric ratios of amino acids in water extracts of the A-12236 meteorite and another primitive CM chondrite Elephant Moraine (EET) 96029 (CM2.7) determined by ultra-high-performance liquid chromatography time-of-flight mass spectrometry. EET 96029 was highly depleted in amino acids and dominated by glycine, while a wide diversity of twoto six-carbon aliphatic primary amino acids were identified in A-12236, which had a total amino acid abundance of 360 ! 18 nmol g"1, with most amino acids present without hydrolysis (free). The amino acid concentrations of A-12236 were double those previously measured in the CM2.7 Paris meteorite, consistent with A-12236 being a highly primitive and unheated CM chondrite. The high relative abundance of a-amino acids in A-12236 is consistent with formation by a Strecker-cyanohydrin dominated synthesis during a limited early aqueous alteration phase on the CM meteorite parent body. The presence of predominantly free glycine, a near racemic mixture of alanine (D/L ~0.93–0.96), and elevated abundances of several terrestrially rare nonprotein amino acids including a-aminoisobutyric acid (a-AIB) and racemic isovaline indicate that these amino acids in A-12236 are extraterrestrial in origin. Given a lack of evidence for biological amino acid contamination in A-12236, it is possible that some of the Lenantiomeric excesses (Lee ~34–64%) of the protein amino acids, aspartic and glutamic acids and serine, are indigenous to the meteorite; however, isotopic measurements are needed for confirmation. In contrast to more aqueously altered CMs of petrologic types ≤2.5, no Lisovaline excesses were detected in A-12236. This observation strengthens the hypothesis that extensive parent body aqueous activity is required to produce or amplify the large L-isovaline excesses that cannot be explained solely by exposure to circularly polarized radiation or other chiral symmetry breaking mechanisms prior to incorporation into the asteroid parent body.

中文翻译：

---

原始 CM 碳质球粒陨石 Asuka 12236 中丰富的外星氨基酸

Asuka (A)-12236 陨石最近被归类为岩石学类型 3.0/2.9 的 CM 碳质球粒陨石，是迄今为止研究过的最原始的 CM 陨石之一。在这里，我们报告了 A-12236 陨石和另一种原始 CM 球粒陨石象碛 (EET) 96029 (CM2.7) 的水提取物中氨基酸的浓度、相对分布和对映体比率，通过超高效液相色谱法测定飞行时间质谱。EET 96029 的氨基酸高度耗尽，以甘氨酸为主，而在 A-12236 中鉴定出广泛多样的二至六碳脂肪族一级氨基酸，其总氨基酸丰度为 360 ! 18 nmol g"1，大多数氨基酸存在而不水解（游离）。A-12236 的氨基酸浓度是之前在 CM2.7 巴黎陨石中测得的氨基酸浓度的两倍，这与 A-12236 是高度原始且未加热的 CM 球粒陨石一致。A-12236 中 a-氨基酸的高相对丰度与在 CM 陨石母体上有限的早期含水蚀变阶段期间由 Strecker-氰醇主导的合成形成一致。主要存在游离甘氨酸、丙氨酸的近外消旋混合物 (D/L ~0.93–0.96) 以及几种地球上罕见的非蛋白质氨基酸（包括 a-氨基异丁酸 (a-AIB) 和外消旋异缬氨酸）的丰度升高表明这些氨基A-12236 中的酸是来自外星的。鉴于缺乏 A-12236 中生物氨基酸污染的证据，某些蛋白质氨基酸、天冬氨酸、谷氨酸和丝氨酸的Lenantiomeric过量（Lee~34-64%）可能是陨石的原生物质；但是，需要进行同位素测量以进行确认。与岩石学类型≤2.5 的更多水性改变的 CM 相比，在 A-12236 中未检测到 Lisovaline 过量。这一观察结果强化了这样一种假设，即需要广泛的母体水活动来产生或放大大量的 L-异缬氨酸过量，这不能仅通过在并入小行星母体之前暴露于圆极化辐射或其他手性对称破坏机制来解释。与岩石学类型≤2.5 的更多水性改变的 CM 相比，在 A-12236 中未检测到 Lisovaline 过量。这一观察结果强化了这样一种假设，即需要广泛的母体水活动来产生或放大大量的 L-异缬氨酸过量，这不能仅通过在并入小行星母体之前暴露于圆极化辐射或其他手性对称破坏机制来解释。与岩石学类型≤2.5 的更多水性改变的 CM 相比，在 A-12236 中未检测到 Lisovaline 过量。这一观察结果强化了这样一种假设，即需要广泛的母体水活动来产生或放大大量的 L-异缬氨酸过量，这不能仅通过在并入小行星母体之前暴露于圆极化辐射或其他手性对称破坏机制来解释。