Metal-catalyzed phosphorylation by phosphite and energy at origins

How did phosphate become the universal energetic currency of life? Traditional approaches to phosphorylation in early evolution studies entail non-physiological conditions. Phosphite, HPO₃^2-, which is oxidized enzymatically by many microbes and which naturally occurs in serpentinizing hydrothermal vents, readily phosphorylates ribose, glucose, glycerol, serine, AMP, creatine and acetate to generate phosphoester, phosphoanhydride and acylphosphate bonds in hours to days at 25-100 °C in pure alkaline water. These reactions are thermodynamically favorable because anoxic phosphite oxidation to phosphate and H₂ is highly exergonic. But the reactions do not proceed without catalysts. The most effective catalyst yet identified is a nanoparticular form of a shiny metal: zero-valent (native, or elemental) palladium (Pd⁰). Native palladium, like phosphite, also naturally occurs in serpentinizing hydrothermal vents, as do other native platinum group elements (PGE), including Pt, Rh, Ru and Ir. Here we survey the use of standard currencies of biochemical energy used in core biosynthesis of amino acids, bases and cofactors from H₂, CO₂, NH₃, H₂S, H₂O and P_i, their frequency is phosphate > redox > thioesters. We test PGE as catalysts of phosphite oxidation and phosphorylation. Although all metals tested readily oxidize phosphite, only Pd⁰ efficiently catalyzes phosphorylation, generating phosphorylated products at physiologically relevant concentrations. In phosphorylation reactions via phosphite oxidation, a portion of the energy released is conserved in phosphorylated products, as in biological energy conservation. Favorable thermodynamics of aqueous phosphite-dependent phosphorylation reactions suggest their possible involvement in the origin of metabolism.