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

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, Δ, which determine whether a reaction can go forward or not, should help specify the source. By calculating values of Δ across the conserved and universal core of 402 individual reactions that synthesize amino acids, nucleotides and cofactors from H, CO, NH, HS and phosphate in modern cells, we find that 95-97% of these reactions are exergonic (Δ ≤ 0 kJ⋅mol) at pH 7-10 and 80-100°C under nonequilibrium conditions with H replacing biochemical reductants.