  alcohol dehydrogenases (adh) () are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (nad+ to nadh). in humans and many other animals, they serve to break down alcohols that otherwise are toxic, and they also participate in generation of useful aldehyde, ketone, or alcohol groups during biosynthesis of various metabolites. in yeast, plants, and many bacteria, some alcohol dehydrogenases catalyze the opposite reaction as part of fermentation to ensure a constant supply of nad+. == evolution == genetic evidence from comparisons of multiple organisms showed that a glutathione-dependent formaldehyde dehydrogenase, identical to a class iii alcohol dehydrogenase (adh-3/adh5), is presumed to be the ancestral enzyme for the entire adh family. early on in evolution, an effective method for eliminating both endogenous and exogenous formaldehyde was important and this capacity has conserved the ancestral adh-3 through time. from genetic duplications of adh-3, followed by series of mutations, the other adhs evolved. the ability to produce ethanol from sugar is believed to have initially evolved in yeast. this feature is not adaptive from an energy point of view but, by making alcohol in such high concentrations so that they would be toxic to other organisms,
Alcohol_and_health EC_1.1.1 Genes_on_chromosome_4 Iron_enzymes NADH-dependent_enzymes Protein_families Zinc_enzymes