Stereospecificity of myo-inositol hexakisphosphate dephosphorylation by a phytate-degrading enzyme of baker's yeast

During food processing such as baking, phytate is dephosphorylated to produce degredation products, such as myo-inositol pentakis-, tetrakis-, tris-, bis-, and monophosphates. Certain myo-inositol phosphates have been proposed to have positive effects on human health. The position of the phosphate groups on the myo-inositol ring is thereby of great significance for their physiological functions. Using a combination of high-performance ion chromatography analysis and kinetic studies the stereospecificity of mya-inositol hexakisphosphate dephosphorylation by a phytate-degrading enzyme from baker's yeast.(Saccharomyces cerevisiae) was established. The data demonstrate that the phytate-degrading enzyme from baker's yeast dephosphorylates myo-inositol hexakisphosphate in a stereospecific way by sequential removal of phosphate groups via D-Ins(1,2,4,5,6)P(5), D-Ins-(1,2,5,6)P(4), D-Ins(1,2,6)P(3), D-Ins(1,2,6)Pa(2) to finally Ins(2)P (notation 3/4/5/6/1). Knowledge of the absolute stereochemical-specificity of the baker's yeast phytase allows use of the enzyme to produce defined myo-inositol phosphates for kinetic and physiological studies.