Distributions of amino acids, based on either enantiomeric excess or relative abundances of amino acid type, are key chemical measurements in the search for life on potential future astrobiology missions. This study investigates the impact of subcritical water extraction (SCWE) at different pH values on the measurement of these amino acid distributions when the starting material contains microorganisms. Cells of Pseudoalteromonas haloplanktis at pH 2, 6, and 12 underwent SCWE at 200 °C for 30 min, and the released amino acids were analyzed by capillary electrophoresis with laser-induced fluorescence detection. The overall extraction yield was improved under both acidic and alkaline conditions relative to neutral ones. The characteristic biotic distributions of amino acid types present in these samples were preserved under all conditions, although some degradation was observed as a relative increase in the amount of simpler amino acids like glycine. Contrarily, while biotic enantiomeric excesses remained preserved under acidic conditions, racemization was observed under alkaline conditions. This work shows the power of SCWE for converting polypeptide biopolymers into amino acid monomers, independent of the initial pH of the sample. However, it also highlights the need to understand the physiochemical properties of the sample to allow the mitigation of undesirable changes to the native distributions of amino acids.

中文翻译：

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pH 对亚临界水萃取微生物释放氨基酸的影响

基于氨基酸类型的对映体过量或相对丰度的氨基酸分布是未来潜在天体生物学任务中寻找生命的关键化学测量。本研究探讨了当起始材料含有微生物时，不同 pH 值下的亚临界水萃取 (SCWE) 对这些氨基酸分布测量的影响。pH 2、6 和 12 的盐生假交替单胞菌细胞在 200 °C 下进行 SCWE 30 分钟，并通过毛细管电泳和激光诱导荧光检测来分析释放的氨基酸。相对于中性条件，酸性和碱性条件下的总提取率均有所提高。这些样品中存在的氨基酸类型的特征生物分布在所有条件下都得到保留，尽管观察到一些降解是由于更简单的氨基酸（如甘氨酸）的量相对增加而发生的。相反，虽然在酸性条件下仍然保留生物对映体过量，但在碱性条件下观察到外消旋化。这项工作展示了 SCWE 将多肽生物聚合物转化为氨基酸单体的能力，与样品的初始 pH 无关。然而，它也强调需要了解样品的理化特性，以减轻氨基酸天然分布的不良变化。