Stereospecificity of myo-inositol hexakisphosphate dephosphorylation by a phytate-degrading enzyme of Escherichia coli

Using a combination of high-performance ion chromatography analysis and kinetic studies, the stereospecificity of myo-inositol hexakisphosphate dephosphorylation by the phytate-degrading enzyme P2 of Escherichia coli was established. High-performance ion chromatography revealed that the phytate-degrading enzyme P2 of E. coli degrades myo-inositol hexakisphosphate by stepwise dephosphorylation via D/L-Ins(1,2,3,4,5)P-5, D/L-Ins(2,3,4,5)P-4, D/L-Ins(2,4,5)P-3 or D/L-Ins(1,2,4)P-3, D/L-Ins(1,2)P-2 or Ins(2,5)P-2 or D/L-Ins(4,5)P-2 to finally Ins(2)P or Ins(S)P-4, Kinetic parameters for myo-inositol pentakisphosphate hydrolysis by E. coli and wheat phytase, respectively, showed that the myo-inositol pentakisphosphate intermediate produced either by the phytate-degrading enzyme of wheat or E. coli are not identical. The absolute configuration of the myo-inositol pentakisphosphate isomer produced by the E. coli enzyme was determined by taking into consideration that wheat phytase produces predominantly the n-Ins(1,2,3,5,6)P-5 isomer (Lim, P.E., Tate, M.E., 1973. The phytases: II. Properties of phytase fraction F-1 and F-2 from wheat bran and the myo-inositol phosphates produced by fraction F-2. Biochim. Biophys. Acta 302, 326-328). The data demonstrate that the phytate-degrading enzyme P2 of E. coli dephosphorylates myo-inositol hexakisphosphate in a stereospecific way by sequential removal of phosphate groups via D-Ins(1,2,3,4,5)P-5, D-Ins(2,3,4,5)P-4, D-Ins(2,4,5)P-3, Ins(2,5)P-2 to finally Ins(2)P (notation 6/1/3/4/5). (C) 2000 Elsevier Science B.V. All rights reserved.