Catalyzes the isomerization of 5-dehydro-4-deoxy-D-glucuronate to 3-deoxy-D-glycero-2,5-hexodiulosonate (By similarity). Plays a role in the catabolism of hexuronates under osmotic stress conditions, likely substituting for the regular hexuronate degrading enzyme UxaC whose expression is repressed in these conditions (PubMed:23437267). 5-dehydro-4-deoxy-D-glucuronate = 3-deoxy-D-glycero-2,5-hexodiulosonate Binds 1 zinc ion per subunit. The bound metal seen in the crystal structure was tentatively identified as zinc, and its requirement for activity has not been shown. Glycan metabolism; pectin degradation; 2-dehydro-3-deoxy-D-gluconate from pectin: step 4/5. Homohexamer. Its expression is up-regulated in the presence of galacturonate and glucuronate (PubMed:23437267). Is also down-regulated in E.coli of mice fed a casein-rich diet (PubMed:22427493). Belongs to the KduI family.