Analysis of myo-inositol hexakisphosphate hydrolysis by Bacillus phytase: indication of a novel reaction mechanism

Phytic acid (myo-inositol hexakisphosphate, InsP(6)) hydrolysis by Bacillus phytase (PhyC) was studied. The enzyme hydrolyses only three phosphates fr om phytic acid. Moreover, the enzyme seems to prefer the hydrolysis of ever y second phosphate over that of adjacent ones. Furthermore, it is very like ly that the enzyme has two alternative pathways for the hydrolysis of phyti c acid, resulting in two different myo-inositol trisphosphate end products: Ins(2,4,6)P-8 and Ins(1,3,5)P-3. These results, together with inhibition s tudies with fluoride, vanadate, substrate and a substrate analogue, indicat e a reaction mechanism different from that of other phytases. By combining the data presented in this study with (1) structural information obtained f rom the crystal structure of Bacillus amyloliquefaciens phytase [Ha, Oh, Sh in, Kim, Oh, Kim, Choi and Oh (2000) Nat. Struct. Biol. 7, 147-153], and (2 ) computer-modelling analyses of enzyme-substrate complexes, a novel mode o f phytic acid hydrolysis is proposed.