Phosphatase with broad specificity; it can dephosphorylate fructose 1,6-bisphosphate, both D and L isomers of inositol-1-phosphate (I-1-P), 2'-AMP, pNPP, beta-glycerol phosphate, and alpha-D-glucose-1-phosphate. Cannot hydrolyze glucose-6-phosphate, fructose-6-phosphate, NAD(+) or 5'-AMP. May be involved in the biosynthesis of a unique osmolyte, di-myo-inositol 1,1-phosphate. beta-D-fructose 1,6-bisphosphate + H2O = beta-D-fructose 6-phosphate + phosphate a myo-inositol phosphate + H2O = myo-inositol + phosphate IMPase activity is inhibited by Ca(2+) and Zn(2+). In contrast to mammalian I-1-P phosphatases, is not inhibited by Li(+) up to 100 mM. kcat is 4.2 sec(-1) for IMPase activity (at 85 degrees Celsius) and 7.0 sec(-1) for FBPase activity (at 85 degrees Celsius). Is thermostable. After incubation at 85 degrees Celsius for 30 minutes, more than 95% of I-1-Pase activity remains. Homodimer. Belongs to the inositol monophosphatase superfamily. FBPase class 4 family.