Effect of myo-inositol(1,4,5)trisphosphate on the hydrolysis of phytic acid by phytase.

Phytase is a monomeric enzyme of molecular mass 160 kDa which catalyzes the hydrolysis of phytic acid (D-myo inositol hexakisphosphate, InsP6) in a stepwise manner to myo-inositol. The enzyme-InsPn (n = 1-6) interaction at the catalytic site has a dissociation constant in the micro molar range. There also exists in the enzyme, a non-catalytic site specific for InsP3 with dissociation constant in the nano molar range. We have probed the effect of the high affinity InsP3 binding on the dissociation constant (Kd) of the phytase-InsP6 interaction and the kinetics of hydrolysis. These studies demonstrate the effect exerted by the high affinity InsP3 binding on the catalytic site of the enzyme.