Catalyzes the dehydration of L-arabonate to L-2-keto-3-deoxyarabonate (L-KDA). Is involved in a degradation pathway of L-arabinose that allows A.brasilense to grow on L-arabinose as a sole carbon source. To a lesser extent, can also use D-xylonate as substrate, but not D-galactonate, D-arabonate, and D-gluconate. L-arabinonate = 2-dehydro-3-deoxy-L-arabinonate + H2O Binds 1 [4Fe-4S] cluster. Activity is enhanced by Mg(2+), being optimal with a concentration of 1-10 mM Mg(2+). Homodimer. Belongs to the IlvD/Edd family.