The Autotrophic Core: An Ancient Network of 404 Reactions Converts H(2), CO(2), and NH(3) into Amino Acids, Bases, and Cofactors

The metabolism of cells contains evidence reflecting the process by which they arose. Here, we have identified the ancient core of autotrophic metabolism encompassing 404 reactions that comprise the reaction network from H(2), CO(2), and ammonia (NH(3)) to amino acids, nucleic acid monomers, and the 19 cofactors required for their synthesis. Water is the most common reactant in the autotrophic core, indicating that the core arose in an aqueous environment. Seventy-seven core reactions involve the hydrolysis of high-energy phosphate bonds, furthermore suggesting the presence of a non-enzymatic and highly exergonic chemical reaction capable of continuously synthesizing activated phosphate bonds. CO(2) is the most common carbon-containing compound in the core. An abundance of NADH and NADPH-dependent redox reactions in the autotrophic core, the central role of CO(2), and the circumstance that the core’s main products are far more reduced than CO(2) indicate that the core arose in a highly reducing environment. The chemical reactions of the autotrophic core suggest that it arose from H(2), inorganic carbon, and NH(3) in an aqueous environment marked by highly reducing and continuously far from equilibrium conditions. Such conditions are very similar to those found in serpentinizing hydrothermal systems.