Enzyme Specificity for the Degradation of Phytate: Isotope As a Proxy for Tracking Active Enzyme in the Environment.

Enzyme specificity for the degradation of phytate: Isotope as a proxy for tracking active enzyme in the environment Mingjing Sun and Deb Jaisi Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716 ABSTRACT Phytate is the most common organic phosphorous compound particularly in agricultural soils. Phytate is quite stable in non-enzymatic reactions but it could be degraded rapidly in the presence of phosphohydrolase enzymes. Different enzymes hydrolyze phytate but their specificity, degradation pathways and products as well as isotope effect vary. In this research, we investigated phytate degradation by four common phosphohydrolase enzymes (phytase from wheat and Aspergillus niger and acid phosphatase from wheat germ and potato) using a combination of ion chromatography (IC), nuclear magnetic resonance (NMR) spectrometry, and stable isotope ratios mass spectrometry (IRMS). The results show that phytase from wheat and Aspergillus niger and acid phosphatase from wheat germ could release 5 moles of orthophosphates (Pi) from a mole of phytate, while acid phosphatase from potato could release all. The phosphate oxygen isotope ratios of released Pi at different times are found to be almost constant for a particular enzyme indicating all the phosphate moieties in phytate ring are isotopically identical. However, the phosphate oxygen isotope ratios of released Pi are different among enzymes by up to 2 ¡ë. These differences are due to different isotope fractionation effects among enzymes. The distinct isotope effect for each enzyme could be a useful proxy to differentiate the active enzymes present during phytate hydrolysis in the environment.