Responsible for the provision of inositol required for synthesis of phosphatidylinositol and polyphosphoinositides and has been implicated as the pharmacological target for lithium action in brain. Has broad substrate specificity and can use myo-inositol monophosphates, myo-inositol 1,3-diphosphate, myo-inositol 1,4-diphosphate, scyllo-inositol-phosphate, glucose-1-phosphate, glucose-6-phosphate, fructose-1-phosphate, beta-glycerophosphate, and 2'-AMP as substrates (By similarity). Is equally active with myo-inositol monophosphate and D-galactose 1-phosphate. a myo-inositol phosphate + H2O = myo-inositol + phosphate alpha-D-galactose 1-phosphate + H2O = D-galactose + phosphate Activity with myo-inositol monophosphate and D-galactose 1-phosphate is inhibited by Li(+), Ca(2+) and Mn(2+), but also by Mg(2+) at concentrations above 3 mM. Polyol metabolism; myo-inositol biosynthesis; myo-inositol from D-glucose 6-phosphate: step 2/2. Homodimer. The N-terminus is blocked. Belongs to the inositol monophosphatase superfamily.