Phytate Degradation by Different Phosphohydrolase Enzymes: Contrasting Kinetics, Decay Rates, Pathways, and Isotope Effects

Phytate (IP6) is often the most common organic P compound particularly in agricultural soils. Understanding the fate of inositol phosphate (IPx) in the environment in terms of isomeric composition and concentration and assessing relative resistance to (or preference for) degradation is essential to estimate the potential role of IPx in generating inorganic P (Pi) as well as overall P cycling in the environment. In this study, we analyzed IP6 degradation by four common phosphohydrolase enzymes (phytase from wheat [Triticum aestivum L.] and Aspergillus niger and acid phosphatase from wheat germ and potato [Solanum tuberosum L.]), with particular focus on degradation pathways, isomer kinetic decay rate, and isotope effects using a combination of high-performance ion chromatography, nuclear magnetic resonance, stable isotopes, and process-based modeling techniques. Our results show that the degradation pathways are often distinct among enzymes. The process-based Bayesian inverse modeling was used to capture the trend and magnitude of the measured concentrations for each IPx isomer and to determine the decay constants. Furthermore, O isotope ratios (delta O-18(P)) of released Pi enabled the identification of isotopically identical phosphate moieties in phytate derived from natural sources. Distinctly different fractionation factors, degradation pathways, and kinetic decay rate coefficients among the enzymes studied could lead to potential discrimination and tracking of phytate sources and products as well as active enzymes present in the environment.