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 produ ce degredation products, such as myo-inositol pentakis-, tetrakis-, tris-, bis-, and monophosphates. Certain myo-inositol phosphates have been propose d to have positive effects on human health. The position of the phosphate g roups on the myo-inositol ring is thereby of great significance for their p hysiological functions. Using a combination of high-performance ion chromat ography 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 t hat the phytate-degrading enzyme from baker's yeast dephosphorylates myo-in ositol hexakisphosphate in a stereospecific way by sequential removal of ph osphate 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 th e absolute stereochemical-specificity of the baker's yeast phytase allows u se of the enzyme to produce defined myo-inositol phosphates for kinetic and physiological studies.