Myo-lnositol phosphate isomers generated by the action of a phytate-degrading enzyme from Klebsiella terrigena on phytate

摘要

For the first time a dual pathway for dephosphorylation of myo-inositol hexakisphosphate by a histidine acid phytase was established. The phytate-degrading enzyme of Klebsiella terrigena degrades mvc-inositol hexakisphosphate by stepwise dephosphorylation, preferably via D-Ins(l,2,4,5,6)P_5, D-Ins(l,2,5,6)P_4, D-Ins(l,2,6)P_3, D-Ins(l,2)P_2 and alternatively via D-Ins(l,2,4,5,6)P_5, Ins(2,4,5,6)P_4, D-Ins(2,4,5)P_3, o-Ins(2,4)P_2 to finally Ins(2)P. It was estimated that more than 98% of phytate hydrolysis occurs via D-Ins(l,2,4,5,6)P_5. Therefore, the phytate-degrading enzyme from K. terrigena has to be considered a 3-phytase (EC 3.1.3.8). A second dual pathway of minor importance could be proposed that is in accordance with the results obtained byanalysis of the dephosphorylation products formed by the action of the phytate-degrading enzyme of K. terrigena on myo-inositol hexakisphosphate. It proceeds preferably via D-Ins(l,2,3,5,6)P_5, D-Ins(l,2,3,6)P_4, Ins(l,2,3)P_3, D-Ins(2,3)P_2 and alternatively via D-Ins(l,2,3,5,6)P_5, D-Ins(2,3,5,6)P_4, D-Ins(2,3,5)P_3, D-Ins(2,3)P_2 to finally Ins(2)P. D-Ins(2,3,5,6)P_4, D-Ins(2,3,5)P_3, and D-Ins(2,4)P_2 were reported for the first time as intermediates of enzymatic phytate dephosphorylation. A role of the phytate-degrading enzyme from K. terrigena in phytate breakdown could not be ruled out. Because of its cytoplasmatic localization and the suggestions for substrate recognition, alpha-Ins(l,3,4,5,6)P_5 might be the natural substrate of this enzyme and, therefore, may play a role in microbial pathogenesis or cellular wryo-inositol phosphate metabolism.