Metabolic homeostasis and growth in abiotic cells

Metabolism constitutes the core chemistry of life. How it began on the early Earth and whether it had a cellular origin is still uncertain. A leading hypothesis for lifes origins postulates that metabolism arose from geochemical CO2-fixing pathways, driven by inorganic catalysts and energy sources, long before enzymes or genes existed. The acetyl-CoA pathway and the reductive tricarboxylic acid cycle are considered ancient reaction networks that hold relics of early carbon-fixing pathways. Although transition metals can promote many steps of these pathways, whether they form a functional metabolic network in abiotic cells has not been shown. Here, we formulate a nonenzymatic carbonfixing network from these pathways and determine its functional feasibility in abiotic cells by imposing the fundamental physico-chemical constraints of the early Earth. Using first principles, we show that abiotic cells could have sustainable steady carbon-fixing cycles that perform a systemic function over a relatively narrow range of conditions. Furthermore, we find that in all feasible steady states, the operation of the cycle elevates the osmotic pressure, leading to volume expansion. These results suggest that achieving homeostatic metabolic states under prebiotic conditions was possible, but challenging, and volume growth was a fundamental property of early metabolism.