TITLE: Quantitative benchmarking of the catalytic parameters for enzyme-mimetic ribnucleotide dephosphorylation by iron oxide mineralss
—ABSTRACT: Iron oxides, which are documented phosphorus (P) sinks, are 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 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 (Pi). Matrix-assisted laser desorption/ionization with mass spectrometry demonstrated short-lived triphosphorylated and monophosphorylated ribonucleotides bound to goethite. Kinetic monitoring of both dissolved and mineral-bound Pi from triphosphorylated ribonucleotides revealed that maximal production rates with goethite (1.9–16.1 μmol Pi h-1 ggoethite-1) were >five-fold higher than with hematite and ferrihydrite; monophosphorylated ribonucleotides generated only mineral-bound Pi, at similar rates (0.0–12.9 μmol Pi h-1 gmineral-1) across minerals. No clear distinction was observed between purine-based and pyrimidine-based ribonucleotides. After normalization to mineral-dependent Pi binding capacity, resulting catalytic turnover rates implied surface chemistry-controlled reactivity. Ribonucleotide-mineral complexation mechanisms were identified with infrared spectroscopy and molecular modeling. Our kinetic parameters estimated iron oxide-catalyzed rates in soil (0.01–5.5 μmol Pi h-1 gsoil) comparable to reported soil phosphatase rates, highlighting both minerals and enzymes as relevant catalysts in P cycling. [Link to Open Access Article]