Catalyzes the reversible reduction of 2,5-diketo-3-deoxygluconate (DKII or 4,6-dihydroxy-2,5-dioxohexanoate) into 2-keto-3-deoxygluconate (KDG or 2-dehydro-3-deoxygluconate) with a concomitant oxidation of NADH (Ref.4). To a lesser extent, can also reduce 5-keto-D-gluconate and oxidize D-gluconate and 1,2-propanediol. Together with KduI, seems to play a role in the catabolism of hexuronates under osmotic stress conditions, substituting for the regular hexuronate degrading enzymes UxaABC and UxuAB whose expression is repressed in these conditions. In vitro, also exhibits NADH-dependent 20-ketosteroid reductase activity against eukaryotic steroid hormone 11-deoxycorticosterone (11-DOC), which is converted into the product 4-pregnen-20,21-diol-3-one. In addition to 11-DOC, five other C21 steroid compounds (11-deoxycortisol, cortisol, corticosterone, cortisone, and 21-hydroxypregnenolone) are reduced by KduD, but steroids lacking the hydroxyl group at C21 position, such as pregnenolone, testosterone propionate, cortisone acetate, or progesterone, cannot be used as substrate.