Reactivity landscape of pyruvate under simulated hydrothermal vent conditions

Abstract

Pyruvate is an important "hub" metabolite that is a precursor for amino acids, sugars, cofactors, and lipids in extant metabolic networks. Pyruvate has been produced under simulated hydrothermal vent conditions from alkyl thiols and carbon monoxide in the presence of transition metal sulfides at 250°C [Cody GD et al. (2000) Science 289(5483):1337-1340], so it is plausible that pyruvate was formed in hydrothermal systems on the early earth. We report here that pyruvate reacts readily in the presence of transition metal sulfide minerals under simulated hydrothermal vent fluids at more moderate temperatures (25-110°C) that are more conducive to survival of biogenic molecules. We found that pyruvate partitions among five reaction pathways at rates that depend upon the nature of the mineral present; the concentrations of H 2 S, H 2 , and NH 4 Cl; and the temperature. In most cases, high yields of one or two primary products are found due to preferential acceleration of certain pathways. Reactions observed include reduction of ketones to alcohols and aldol condensation, both reactions that are common in extant metabolic networks. We also observed reductive amination to form alanine and reduction to form propionic acid. Amino acids and fatty acids formed by analogous processes may have been important components of a protometabolic network that allowed the emergence of life.catalysis | prebiotic chemistry | abiogenesis B aross and Hoffman suggested in 1985 that life emerged in or around hydrothermal vents from a protometabolic network fueled by small molecules such as CO 2 , NH 3 , and H 2 in hydrothermal fluids (1). The existence of dense biological communities sustained solely by the chemicals and energy provided by vent fluids proves that these habitats are capable of supporting life. The possibility that life originated at such sites is appealing for a number of reasons. Pores in vent walls and the surrounding fractured crust could have provided compartmentalization before the availability of lipid membranes. The mineral surfaces lining these compartments could have catalyzed the formation of organic compounds from the constituents of vent fluids. Temperature gradients in hydrothermal systems could have allowed reactions with high activation energies to occur in the internal hot regions as well as formation of more fragile molecules near the cool outer wall. In addition, both theoretical and experimental studies have demonstrated that thermal gradients can lead to massive concentration of molecules in small regions of microchannels due to a combination of convection and thermophoresis (2, 3). This physical mechanism would enhance the rates of second-order reactions between molecules originating from chemical reactions in hydrothermal fluids as they percolate through pores and channels in vent structures and in cracks in the surrounding crust.An important challenge for prebiotic chemists is to explore the potential for synthesis of complex organic molecules from geochemical precursors in hydrothermal environments. In...

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

“…Iron sulfides have also been shown to be capable of driving reductive amination of α-keto acids to form amino acids (31,32). However, Huber and Wächtershäuser (32) found that amino acid synthesis did not occur with freshly precipitated sulfides of other metals including Zn, Mn, Co, Cu, and Ni and that replacing the Fe(II) with Ni(II) in sulfide precipitates simply decreased the amino acid yield proportional to the decreased concentration of Fe.…”

“…presence of sulfide), and the amino acid alanine (in the presence of ammonia) (31)(32)(33). Novikov and Copley (31) showed that, even when ammonia was present, the yield of alanine synthesis from pyruvate (and whether alanine formed at all in favor of some other product) was dependent on which mineral was present.…”

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