Involved in the degradation of glucose and galactose via the nonphosphorylative variant of Entner-Doudoroff pathway. Catalyzes the dehydration of gluconate to produce 2-keto-3-deoxygluconate (KDG). It is also able to catalyze the dehydration of galactonate to produce 2-keto-3-deoxygalactonate (KDGal). D-gluconate = 2-dehydro-3-deoxy-D-gluconate + H2O D-gluconate = 2-dehydro-3-deoxy-D-gluconate + H2O D-galactonate = 2-dehydro-3-deoxy-D-galactonate + H2O D-galactonate = 2-dehydro-3-deoxy-D-galactonate + H2O Binds 1 Mg(2+) ion per subunit. Optimum pH is between 6. Optimum temperature is 70 degrees Celsius). Carbohydrate acid metabolism; D-gluconate degradation. Homooctamer. Constitutively expressed. Belongs to the mandelate racemase/muconate lactonizing enzyme family. GaD subfamily.