myo-Inositol phosphate isomers generated by the action of a phytate-degrading enzyme from Klebsiella terrigena on phytate
Artikel i vetenskaplig tidskrift, 2006
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 myo-inositol hexakisphosphate by stepwise dephosphorylation, preferably 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)P-2 and alternatively via D-Ins(1,2,4,5,6)P-5, Ins(2,4,5,6)P-4, D-Ins(2,4,5)P-3, D-Ins(2,4)P-2 to finally Ins(2)P. It was estimated that more than 98% of phytate hydrolysis occurs via D-Ins(1,2,4,5,6)P-5. Therefore, the phytate-degrading enzyme from K. terrigena has to be considered a 3-phytase (EC 18.104.22.168). A second dual pathway of minor importance could be proposed that is in accordance with the results obtained by analysis 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(1,2,3,5,6)P-5, D-Ins(1,2,3,6)P-4, Ins(1,2,3)P-3, D-Ins(2,3)P-2 and alternatively via D-Ins(1,2,3,5,6)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, D-Ins(1,3,4,5,6)P-5 might be the natural substrate of this enzyme and, therefore, may play a role in microbial pathogenesis or cellular myo-inositol phosphate metabolism.Key words: myo-inositol phosphate isomers, phytate-degrading enzyme, phytate, phytase, Klebsiella terrigena.