Barge Laura M, Flores Erika, Baum Marc M, VanderVelde David G, Russell Michael J
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109;
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109.
Proc Natl Acad Sci U S A. 2019 Mar 12;116(11):4828-4833. doi: 10.1073/pnas.1812098116. Epub 2019 Feb 25.
Iron oxyhydroxide minerals, known to be chemically reactive and significant for elemental cycling, are thought to have been abundant in early-Earth seawater, sediments, and hydrothermal systems. In the anoxic Fe-rich early oceans, these minerals would have been only partially oxidized and thus redox-active, perhaps able to promote prebiotic chemical reactions. We show that pyruvate, a simple organic molecule that can form in hydrothermal systems, can undergo reductive amination in the presence of mixed-valence iron oxyhydroxides to form the amino acid alanine, as well as the reduced product lactate. Furthermore, geochemical gradients of pH, redox, and temperature in iron oxyhydroxide systems affect product selectivity. The maximum yield of alanine was observed when the iron oxyhydroxide mineral contained 1:1 Fe(II):Fe(III), under alkaline conditions, and at moderately warm temperatures. These represent conditions that may be found, for example, in iron-containing sediments near an alkaline hydrothermal vent system. The partially oxidized state of the precipitate was significant in promoting amino acid formation: Purely ferrous hydroxides did not drive reductive amination but instead promoted pyruvate reduction to lactate, and ferric hydroxides did not result in any reaction. Prebiotic chemistry driven by redox-active iron hydroxide minerals on the early Earth would therefore be strongly affected by geochemical gradients of E, pH, and temperature, and liquid-phase products would be able to diffuse to other conditions within the sediment column to participate in further reactions.
羟基氧化铁矿物具有化学反应活性且对元素循环具有重要意义，被认为在早期地球的海水、沉积物和热液系统中大量存在。在缺氧且富含铁的早期海洋中，这些矿物仅会部分被氧化，因此具有氧化还原活性，或许能够促进生命起源前的化学反应。我们发现，在热液系统中能够形成的一种简单有机分子丙酮酸，在混合价态的羟基氧化铁存在下可以发生还原胺化反应，生成氨基酸丙氨酸以及还原产物乳酸。此外，羟基氧化铁体系中的pH值、氧化还原和温度的地球化学梯度会影响产物的选择性。当羟基氧化铁矿物中Fe(II):Fe(III)为1:1、处于碱性条件且温度适中时，观察到丙氨酸的产量最高。这些条件例如可能存在于碱性热液喷口系统附近的含铁沉积物中。沉淀物的部分氧化状态对促进氨基酸形成具有重要意义：纯氢氧化亚铁不会驱动还原胺化反应，而是促进丙酮酸还原为乳酸，而氢氧化铁则不会引发任何反应。因此，早期地球上由具有氧化还原活性的氢氧化铁矿物驱动的生命起源前化学过程会受到E、pH值和温度的地球化学梯度的强烈影响，液相产物能够扩散到沉积物柱内的其他条件中参与进一步反应。
