Putative L-iditol 2-dehydrogenase based on annotation of some members in this subgroup. L-iditol 2-dehydrogenase catalyzes the NAD+-dependent conversion of L-iditol to L-sorbose in fructose and mannose metabolism. This enzyme is related to sorbitol dehydrogenase, alcohol dehydrogenase, and other medium chain dehydrogenase/reductases. The zinc-dependent alcohol dehydrogenase (ADH-Zn)-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) to highlight its broad range of activities and to distinguish 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. Active site zinc has a catalytic role, while structural zinc aids in stability. 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.