idnO (Escherichia coli K12): 5-keto-D-gluconate-5-reductase; Catalyzes the reduction of 5-keto-D-gluconate to D-gluconate, using either NADH or NADPH. Is likely involved in an L-idonate degradation pathway that allows E.coli to utilize L-idonate as the sole carbon and energy source. Is also able to catalyze the reverse reaction in vitro, but the D-gluconate oxidation by the enzyme can only proceed with NAD; Belongs to the short-chain dehydrogenases/reductases (SDR) family.