Plays a role in the catabolism of L-fucose. Catalyzes the dehydration of L-fuconate to 2-keto-3-deoxy-L-fuconate by the abstraction of the 2-proton to generate an enediolate intermediate that is stabilized by the magnesium ion. L-fuconate is the preferred substrate with 15-fold lower activity observed for L-galactonate and 8-fold lower activity with D-arabinonate. No activity detected with D-fuconate. Can also catalyze the epimerization of L-talonate and D-ribonate, but at slow rates. L-fuconate = 2-dehydro-3-deoxy-L-fuconate + H2O Binds 1 Mg(2+) ion per subunit. Homodimer. Belongs to the mandelate racemase/muconate lactonizing enzyme family.