Has low dehydratase activity with D-mannonate and D-gluconate, suggesting that these are not physiological substrates and that it has no significant role in the in vivo degradation of these compounds. Has no detectable activity with a panel of 70 other acid sugars (in vitro). D-mannonate = 2-dehydro-3-deoxy-D-gluconate + H2O D-gluconate = 2-dehydro-3-deoxy-D-gluconate + H2O Binds 1 Mg(2+) ion per subunit. kcat is 0.03 sec(-1) with D-mannonate. kcat is 0.05 sec(-1) with D-gluconate. Belongs to the mandelate racemase/muconate lactonizing enzyme family. GalD subfamily.