Inositol hexakisphosphate, often called phytate, is found in abundance in seeds and acting as an inorganic phosphate reservoir. Phytases are phosphatases that hydrolyze phytate to less-phosphorylated myo-inositol derivatives and inorganic phosphate. The active-site sequence (HCXXGXGR) of the phytase identified from the gut micro-organism Selenomonas ruminantium forms a loop (P loop) at the base of a substrate binding pocket that is characteristic of protein tyrosine phosphatases (PTPs). The depth of this pocket is an important determinant of the substrate specificity of PTPs. In humans this enzyme is thought to aid bone mineralization and salvage the inositol moiety prior to apoptosis [3].

1: Structures of the Selenomonas ruminantium phytase in complex with persulfated phytate: DSP phytase fold and mechanism for sequential substrate hydrolysis. Chu HM, Guo RT, Lin TW, Chou CC, Shr HL, Lai HL, Tang TY, Cheng KJ, Selinger BL, Wang AH; Structure. 2004;12:2015-2024. PMID:15530366

2: Effect of ionic strength and oxidation on the P-loop conformation of the protein tyrosine phosphatase-like phytase, PhyAsr. Gruninger RJ, Selinger LB, Mosimann SC; FEBS J. 2008;275:3783-3792. PMID:18573100

3: The human and rat forms of multiple inositol polyphosphate phosphatase: functional homology with a histidine acid phosphatase up-regulated during endochondral ossification. Caffrey JJ, Hidaka K, Matsuda M, Hirata M, Shears SB; FEBS Lett. 1999;442:99-104. PMID:9923613