myo-Inositol phosphate isomers generated by the action of a phytate-degrading enzyme from Klebsiella terrigena on phytate.
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)P5, D-Ins(1,2,5,6)P4, D-Ins(1,2,6)P3, D-Ins(1,2)P2 and alternatively via D-Ins(1,2,4,5,6)P5, Ins(2,4,5,6)P4, D-Ins(2,4,5)P3, D-Ins(2,4)P2 to finally Ins(2)P. It was estimated that more than 98% of phytate hydrolysis occurs via D-Ins(1,2,4,5,6)P5. 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 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)P5, D-Ins(1,2,3,6)P4, Ins(1,2,3)P3, D-Ins(2,3)P2 and alternatively via D-Ins(1,2,3,5,6)P5, D-Ins(2,3,5,6)P4, D-Ins(2,3,5)P3, D-Ins(2,3)P2 to finally Ins(2)P. D-Ins(2,3,5,6)P4, D-Ins(2,3,5)P3, and D-Ins(2,4)P2 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)P5 might be the natural substrate of this enzyme and, therefore, may play a role in microbial pathogenesis or cellular myo-inositol phosphate metabolism.
Greiner
Ralf
R
Centre for Molecular Biology, Federal Research Centre for Nutrition and Food, Haid-und-Neu-Strasse 9, D-76131 Karlsruhe, Germany. ralf.greiner@bfel.de
Carlsson
Nils-Gunnar
NG
D010832:6-Phytase / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D001234:Aspergillus niger / Q000201:enzymology; D001412:Bacillus subtilis / Q000201:enzymology; D002851:Chromatography, High Pressure Liquid; D007295:Inositol Phosphates / Q000378:metabolism; D007536:Isomerism; D007709:Klebsiella / Q000201:enzymology* / Q000378:metabolism; D010833:Phytic Acid / Q000737:chemistry / Q000378:metabolism*
D007295:Inositol Phosphates; D010833:Phytic Acid; D010832:6-Phytase