Catalyzes the reversible epimerization of D-allulose 6-phosphate to D-fructose 6-phosphate. Can also catalyze with lower efficiency the reversible epimerization of D-ribulose 5-phosphate to D-xylulose 5-phosphate. D-allulose 6-phosphate = keto-D-fructose 6-phosphate Binds 1 divalent metal cation per subunit. Activity is highest with Co(2+) > Mn(2+) > Zn(2+). Carbohydrate degradation; D-allose degradation. Homohexamer. Trimer of dimers. Belongs to the ribulose-phosphate 3-epimerase family. AlsE subfamily.