Involved in the degradation of glucose and galactose via the branched variant of the 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. Can also use divalent metal ions such as Co(2+), Mn(2+) and Ni(2+). kcat is 10.4 sec(-1) for gluconate and 1.08 sec(-1) for galactonate (at 70 degrees Celsius and pH 6). kcat is 12.6 sec(-1) for gluconate (at 78 degrees Celsius and pH 7). Optimum pH is between 6.5 and 7.5. Optimum temperature is between 80 and 100 degrees Celsius. At 80 degrees Celsius, the dehydratase is stable for over 2 hours, but at 90 degrees Celsius its activity is decreased to less than 50% in 2 hours and its half-life diminishes to 120 min. At 100 degrees Celsius, the enzyme has a half-life of less than 40 min. The activity is almost undetectable below 60 degrees Celsius. Carbohydrate acid metabolism; D-gluconate degradation. Monomer or homooctamer. D-gluconate dehydratase activity is lost after incubation with phosphatase, whereas no such decrease in activity is observed when the enzymes are incubated in the same reaction mixtures without phosphatase. Analysis of the amino acid sequence of D-gluconate dehydratase indicate the presence of several putative phosphorylation sites on serine, threonine and tyrosine residues. Belongs to the mandelate racemase/muconate lactonizing enzyme family. GaD subfamily.