beta-D-fructose 1,6-bisphosphate + H2O = beta-D-fructose 6-phosphate + phosphate Binds 3 Mg(2+) ions per subunit. Carbohydrate biosynthesis; Calvin cycle. Homotetramer. In photosynthetically active tissues, and in the shoot and root apical meristems. Light activation through pH changes, Mg(2+) levels and also by light-modulated reduction of essential disulfide groups via the ferredoxin-thioredoxin f system. In plants there are two FBPase isozymes: one in the cytosol and the other in the chloroplast. Belongs to the FBPase class 1 family.