Catalyzes the isomerization of 5-dehydro-4-deoxy-D-glucuronate to 3-deoxy-D-glycero-2,5-hexodiulosonate. 5-dehydro-4-deoxy-D-glucuronate = 3-deoxy-D-glycero-2,5-hexodiulosonate Binds 1 zinc ion per subunit. Glycan metabolism; pectin degradation; 2-dehydro-3-deoxy-D-gluconate from pectin: step 4/5. Induced by galacturonate and at a higher level by polygalacturonate. Is expressed under the control of KdgR, but is not controlled by PecS. Is repressed by glucose. Cells lacking this gene are unable to grow on polygalacturonate (PGA) or digalacturonate, but can grow on galacturonate. Belongs to the KduI family.