L-idonate 5-dehydrogenase (L-ido 5-DH ) catalyzes the conversion of L-lodonate to 5-ketogluconate in the metabolism of L-Idonate to 6-P-gluconate. In E. coli, this GntII pathway is a subsidiary pathway to the canonical GntI system, which also phosphorylates and transports gluconate. L-ido 5-DH is found in an operon with a regulator indR, transporter idnT, 5-keto-D-gluconate 5-reductase, and Gnt kinase. L-ido 5-DH is a zinc-dependent alcohol dehydrogenase-like protein. The alcohol dehydrogenase ADH-like family of proteins is a diverse group of proteins related to the first identified member, class I mammalian ADH. This group is also called the medium chain dehydrogenases/reductase family (MDR) which displays a broad range of activities and are distinguished from the smaller short chain dehydrogenases(~ 250 amino acids vs. the ~ 350 amino acids of the MDR). The MDR proteins have 2 domains: a C-terminal NAD(P) binding-Rossmann fold domain of a beta-alpha form and an N-terminal GroES-like catalytic domain. The MDR group contains a host of activities, including the founding alcohol dehydrogenase (ADH), quinone reductase, sorbitol dehydrogenase, formaldehyde dehydrogenase, butanediol DH, ketose reductase, cinnamyl reductase, and numerous others. The zinc-dependent alcohol dehydrogenases (ADHs) catalyze the NAD(P)(H)-dependent interconversion of alcohols to aldehydes or ketones. ADH-like proteins typically form dimers (typically higher plants, mammals) or tetramers (yeast, bacteria), and generally have 2 tightly bound zinc atoms per subunit. The active site zinc is coordinated by a histidine, two cysteines, and a water molecule. The second zinc seems to play a structural role, affects subunit interactions, and is typically coordinated by 4 cysteines.