Gradual assembly of metabolism at a phosphorylating hydrothermal vent

The origin of microbial cells required the emergence of metabolism, an autocatalytic network of roughly 400 enzymatically catalyzed chemical reactions that synthesize the building blocks of life: amino acids, nucleotides and cofactors. Proposals for metabolic origin are theoretical in nature [1-9], empirical studies addressing the origin and early evolution of the 400-reaction chemical network itself are lacking. Here we identify intermediate states in the primordial assembly of metabolism from its inorganic origins, using structure-refined clusters for metabolic enzymes of prokaryotic genomes. We show that metabolism in the last universal common ancestor (LUCA) was enzymatically incomplete, undergoing final assembly independently in the lineages leading to bacteria and archaea, with metal catalysts that predated both enzymes and cofactors providing essential functions. Over half of modern core metabolism corresponds to laboratory reactions catalyzed by native transition metals--Fe(0), Co(0), Ni(0) and their alloys--under conditions of serpentinizing hydrothermal vents. As the hitherto elusive source of primordial aqueous phosphorylation, we show that phosphite, a constituent of serpentinizing systems [10], phosphorylates AMP [11] to ADP using native metals in water. Seventeen cofactors that transfer electrons, nitrogen, and carbon units to substrates in modern metabolism [12] can be functionally replaced by environmental transition metals [13-19]. The data reveal that cofactors are synthesized late in enzymatic metabolism and are required in reactions preceding their synthesis, specifying the existence at origins of simpler precursors, which we identify here as native metals. Cofactors liberated metabolism from a requirement for solid state catalysis at a phosphorylating hydrothermal vent, engendering its autocatalytic state.