Phosphatase with broad specificity; it can dephosphorylate fructose 1,6-bisphosphate, both D and L isomers of inositol-1-phosphate (I-1-P) but displaying a 20-fold higher rate of hydrolysis of D-I-1-P than of the L isomer, 2'-AMP, pNPP, inositol-2-phosphate, beta-glycerol phosphate, and alpha-D-glucose-1-phosphate. Cannot hydrolyze glucose-6-phosphate, fructose-6-phosphate, 5'-AMP and NAD(+). 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 In contrast to mammalian I-1-P phosphatases, is only weakly inhibited by Li(+), since 50% inhibitory concentration for Li(+) is about 100 mM, and the Li(+) concentration required to totally abolish I-1-Pase activity is 1 M. kcat is 207 sec(-1) for IMPase activity (at 95 degrees Celsius) and 268 sec(-1) for FBPase activity (at 95 degrees Celsius). Thermostable. No loss of IMPase activity after incubation at 85 degrees Celsius for 30 minutes. Heating at 100 degrees Celsius for 10 minutes results in a loss of about 20 to 25% of the activity, and 30 minutes at this temperature inactivate about 70% of the activity. Homotetramer. Belongs to the inositol monophosphatase superfamily. FBPase class 4 family.