As these GEITP pages have considered from time to time, how “life” began on Earth is relevant to gene-environment (GxE) interactions — in some ways similar to the relevance of GxE to evolution of life over the past 4+ billion years. In assessing the role of specific geochemical environments and mineral phases when life first emerged, the synthesis of biomolecules (e.g. amino acids, and their condensation into peptides), from geochemical carbon and nitrogen sources, is an important consideration. One type of mineral that would have been abundant — in the mildly acidic, iron-rich oceans of the early Earth — is the iron oxyhydroxides, which can precipitate in a variety of stable or metastable redox states.
Iron oxides/oxyhydroxides are versatile reactive minerals that can drive redox reactions and concentrate phosphorus-containing molecules, trace metals, organic molecules, and other anions. On the early Earth, iron oxyhydroxides and/or “green rust” would likely have been present in oceans — as well as seafloor sediments — playing a fundamental role in elemental cycling and redox chemistry. Iron oxyhydroxides would also have been a primary component in alkaline hydrothermal vents, which have been proposed as the likely environment for emergence of metabolism due to their ambient pH (i.e. acid-base properties), Eh (activity/energy of electrons), ion/chemical, and temperature gradients. In the anoxic (oxygen-starved) iron (Fe2+)-rich early oceans, these minerals would have been only partially oxidized and, thus, redox-active (i.e. perhaps able to promote prebiotic chemical reactions).
Authors [see attached article] show that pyruvate, a simple organic molecule that can form in hydrothermal systems, can undergo reductive amination (conversion of a carbonyl group to an amine, via the intermediate imine) in the presence of mixed-valence iron oxyhydroxides to form the amino acid alanine, as well as the reduced product lactate. Maximal yield of alanine was observed when the iron oxyhydroxide mineral contained 1:1 ratio of Fe(II):Fe(III), under alkaline conditions, and at moderately warm temperatures (these represent conditions that may be found, e.g. in iron-containing sediments near an alkaline hydrothermal vent system). The partially oxidized state of the precipitate was significant in promoting amino acid formation: pure ferrous hydroxides did not drive reductive amination — but instead promoted pyruvate conversion to lactate; moreover, ferric hydroxides did not result in any reaction. Thus, prebiotic chemistry — driven by redox-active iron hydroxide minerals on the early Earth — would have been strongly affected by geochemical gradients of Eh, pH, and temperature. Subsequently, liquid-phase products would be able to diffuse to other conditions within the sediment column to participate in further reactions, leading to the “beginnings of life”. J
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Proc Natl Acad Sci USA 2o19; vol. 116: https://doi.org/10.1073/pnas.1812098116