KINETICS AND PATHWAYS OF PHYTATE DEGRADATION: LINKING ENZYMATIC DEGRADATION TO INCREASED ORTHOPHOSPHATE IN THE ENVIRONMENT

Phytate, the salt of inositol hexakisphosphate, is often the most common organic phosphorus in the natural environment such as in soils and aquatic sediments. The phosphate ester linkage in phytate is quite stable in non-enzymatic reactions. However, the degradation is rather fast in the presence of phytase and thus orthophosphate released from this degradation could exacerbate the water quality. This research compared degradation pathways of phytate degradation using purified phytase from Aspergillus niger and wheat and applied phosphate oxygen isotope ratios in combination with NMR and HPLC to link the degradation products to source through specific isotope effect. The results show that the degradation pathways vary with phytase: for wheat phytase the major pathway follows I(1,2,3,5,6)P₅, I(1,2,5,6)P₄, I(1,2,6)P₃, I(1,2)P₂ and for Aspergillus niger phytase it follows I(1,2,4,5,6)P₅, I(1,2,5,6)P₄, I(1,2,6)P₃, I(1,2)P₂. Interestingly, all phosphate moieties in phytate were found to be isotopically identical. This means that the original source of phytate can be tracked from its partially dephosphorylated products. Overall, these results provided improved insights into the mechanisms and pathways of phytate degradation, particularly the importance of the isotopic tool that can potentially be used for tracking phytate sources and degradation products in the environment.