Quantitative Benchmarking of Catalytic Parameters for Enzyme-Mimetic Ribonucleotide Dephosphorylation by Iron Oxide Minerals

Iron oxides, which are documented phosphorus (P) sinks as adsorbents, have been shown to catalyze organic P dephosphorylation, implicating these minerals as catalytic traps in P cycling. However, quantitative evaluation of this abiotic catalysis is lacking. Here, we investigated the dephosphorylation kinetics of eight ribonucleotides, with different nucleobase structures and P stoichiometry, reacting with common iron oxides. X-ray absorption spectroscopy determined that 0-98% of mineral-bound P was recycled inorganic P (P_i). Matrix-assisted laser desorption/ionization with mass spectrometry demonstrated short-lived triphosphorylated and monophosphorylated ribonucleotides bound to goethite. Based on Michaelis-Menten type modeling of the kinetic evolution of both dissolved and mineral-bound P_i, maximal P_i production rates from triphosphorylated ribonucleotides reacted with goethite (1.9-16.1 μmol P_i h^-1 g_goethite^-1) were >5-fold higher than with hematite and ferrihydrite; monophosphorylated ribonucleotides generated only mineral-bound P_i at similar rates (0.0-12.9 μmol P_i h^-1 g_mineral^-1) across minerals. No clear distinction was observed between purine-based and pyrimidine-based ribonucleotides. After normalization to mineral-dependent P_i binding capacity, resulting catalytic turnover rates implied surface chemistry-controlled reactivity. Ribonucleotide-mineral complexation mechanisms were identified with infrared spectroscopy and molecular modeling. We estimated iron oxide-catalyzed rates in soil (0.01-5.5 μmol P_i h^-1 g_soil) comparable to reported soil phosphatase rates, highlighting both minerals and enzymes as relevant catalysts in P cycling.