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Redox and pH gradients drive amino acid synthesis in iron oxyhydroxide mineral systems

Barge, Laura M. and Flores, Erika and Baum, Marc M. and VanderVelde, David G. and Russell, Michael J. (2019) Redox and pH gradients drive amino acid synthesis in iron oxyhydroxide mineral systems. Proceedings of the National Academy of Sciences of the United States of America, 116 (11). pp. 4828-4833. ISSN 0027-8424.

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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^(2+)-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_h, pH, and temperature, and liquid-phase products would be able to diffuse to other conditions within the sediment column to participate in further reactions.

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Additional Information:© 2019 National Academy of Sciences. Published under the PNAS license. Edited by Donald E. Canfield, University of Southern Denmark, Odense, Denmark, and approved January 9, 2019 (received for review July 28, 2018). PNAS published ahead of print February 25, 2019. We thank Yeghegis Abedian, Kayo Kallas, Liz Miller, Ivria Doloboff, Vince Aguirre, Simonne Jocic, and Amalia E. Castonguay for assistance with experimentation and analysis, and Niklas Thompson for helpful discussions. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA, supported by the NASA Astrobiology Institute Icy Worlds. Author contributions: L.M.B., E.F., M.M.B., D.G.V., and M.J.R. designed research; L.M.B., E.F., M.M.B., and D.G.V. performed research; M.M.B. and D.G.V. contributed new reagents/analytic tools; L.M.B., E.F., M.M.B., and D.G.V. analyzed data; and L.M.B., E.F., M.M.B., D.G.V., and M.J.R. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at
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Official Citation:Redox and pH gradients drive amino acid synthesis in iron oxyhydroxide mineral systems. Laura M. Barge, Erika Flores, Marc M. Baum, David G. VanderVelde, Michael J. Russell. Proceedings of the National Academy of Sciences Mar 2019, 116 (11) 4828-4833; DOI: 10.1073/pnas.1812098116
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93232
Deposited By: Tony Diaz
Deposited On:25 Feb 2019 22:24
Last Modified:12 Mar 2019 21:11

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