Has low D-gluconate dehydratase activity (in vitro), suggesting that it has no significant role in D-gluconate degradation in vivo. Has no detectable activity with a panel of 70 other acid sugars (in vitro). D-gluconate = 2-dehydro-3-deoxy-D-gluconate + H2O Binds 1 Mg(2+) ion per subunit. kcat is 0.04 sec(-1) with D-gluconate. Homotetramer. Belongs to the mandelate racemase/muconate lactonizing enzyme family. GalD subfamily.