Stereochemistry at phosphorus of the reaction catalyzed by myo-inositol monophosphatase.

myo-Inositol monophosphatase (IMPase), the proposed target for lithium therapy for manic depression, is an important enzyme in the biosynthesis of second messengers. Earlier studies have shown that the IMPase-catalyzed hydrolysis of myo-inositol monophosphates to inorganic phosphate and myo-inositol proceeds by direct attack of water at phosphorus. However, research groups have independently proposed either an in-line displacement (with inversion of stereochemistry at phosphorus) or an adjacent attack with a pseudorotation (with retention of stereochemistry at phosphorus). Here, the elucidation of the stereochemical pathway is presented. The IMPase-catalyzed hydrolysis of D-1-S(p)-myo-inositol [(17)O]-thiophosphate in the presence of H(2)(18)O gave inorganic R(p)-[(16)O,(17)O,(18)O]-thiophosphate, with inversion of configuration at phosphorus. This is only consistent with an in-line displacement, and it rules out the controversial adjacent/pseudorotation mechanism. This result will assist in the design of alternative inhibitors of IMPase.