Catalyzes the dehydration of glucarate or L-idarate to 5-keto-4-deoxy-D-glucarate (5-kdGluc) (PubMed:9772162). Also catalyzes the epimerization of D-glucarate and L-idarate (PubMed:11513584). D-glucarate = 5-dehydro-4-deoxy-D-glucarate + H2O Carbohydrate acid metabolism; D-glucarate degradation; 2,5-dioxopentanoate from D-glucarate: step 1/2. Homodimer. Belongs to the mandelate racemase/muconate lactonizing enzyme family. GlucD subfamily.