Hydrogen Fueled Life’s Origins

Amazing stuff!

"... But the metabolism of the planet’s first organisms may not have required an external source of energy. Under the conditions present in a hydrothermal vent, a core set of metabolic reactions unfolds spontaneously in line with the laws of thermodynamics ...
Hydrothermal vents, hot springs near fault lines on the ocean floor, were discovered 40 years ago, and soon after became recognized as environments conducive to the origin of life, as they are warm, rich with minerals, and contain physical and chemical gradients that facilitate reactions. In 2020, Martin and his group showed experimentally that, if kept in water in the presence of the nickel iron alloy awaruite overnight at 100°C, hydrogen gas (which is abundant in hydrothermal vents) will combine with carbon dioxide to form formate, acetate and pyruvate—the latter of which is one of the most central compounds of metabolism. Awaruite catalyzes the formation of pyruvate from hydrogen and carbon dioxide by acting as a reducing agent, allowing it to stand in for the suite of enzymes that usually construct the molecule stepwise in organisms. ...

Martin and his team had previously identified a core set of more than 400 metabolic reactions which would likely have been present in the Last Universal Common Ancestor (LUCA), the organism that gave rise to all extant life on Earth, and are needed to generate amino acids, nucleotides, and other essential cellular molecules. They next asked whether these reactions would have required an external energy source to proceed. 

To find out, the team calculated the Gibbs free energy for each reaction—a thermodynamic measure of the energy needed for or released from a chemical reaction, assuming the surrounding temperature and pressure are kept stable and there are no external inputs. It turns out that under the conditions present in hydrothermal vents, “almost all of the reactions in the metabolism of the last universal common ancestor are downhill,” says Martin—97 percent, to be exact. “That means there’s a natural tendency of metabolism to unfold all by itself, under the right conditions from the elements,” ... “You don’t have to add any energy. ..."

From the abstract:

"Though all theories for the origin of life require a source of energy to promote primordial chemical reactions, the nature of energy that drove the emergence of metabolism at origins is still debated. We reasoned that evidence for the nature of energy at origins should be preserved in the biochemical reactions of life itself, whereby changes in free energy, ΔG ... By calculating values of ΔG across the conserved and universal core of 402 individual reactions that synthesize amino acids, nucleotides and cofactors from H2, CO2, NH3, H2S and phosphate in modern cells, we find that 95–97% of these reactions are exergonic (ΔG ≤ 0 kJ⋅mol−1) at pH 7-10 and 80-100°C under nonequilibrium conditions with H2 replacing biochemical reductants. While 23% of the core’s reactions involve ATP hydrolysis, 77% are ATP-independent, thermodynamically driven by ΔG of reactions involving carbon bonds. We identified 174 reactions that are exergonic by –20 to –300 kJ⋅mol−1 at pH 9 and 80°C and that fall into ten reaction types: six pterin dependent alkyl or acyl transfers, ten S-adenosylmethionine dependent alkyl transfers, four acyl phosphate hydrolyses, 14 thioester hydrolyses, 30 decarboxylations, 35 ring closure reactions, 31 aromatic ring formations, and 44 carbon reductions by reduced nicotinamide, flavins, ferredoxin, or formate. The 402 reactions of the biosynthetic core trace to the last universal common ancestor (LUCA), and reveal that synthesis of LUCA’s chemical constituents required no external energy inputs such as electric discharge, UV-light or phosphide minerals. The biosynthetic reactions of LUCA uncover a natural thermodynamic tendency of metabolism to unfold from energy released by reactions of H2, CO2, NH3, H2S, and phosphate."

Hydrogen Fueled Life’s Origins: Study | The Scientist Magazine® A thermodynamic analysis of more than 400 chemical reactions that likely took place in the ancestor of all life finds most would spontaneously occur at hydrothermal vents, thanks to the hydrogen these geological formations emit.

Energy at Origins: Favorable Thermodynamics of Biosynthetic Reactions in the Last Universal Common Ancestor (LUCA) (open access)