Alcohol dehydrogenase (<db_xref db="EC" dbkey="1.1.1.1"/>) (ADH) catalyzes the reversible oxidation of ethanol to acetaldehyde with the concomitant reduction of NAD:<reaction>Ethanol + NAD = Acetaldehyde + NADH</reaction>Currently three structurally and catalytically different types of alcohol dehydrogenases are known:<ol><li>Zinc-containing 'long-chain' alcohol dehydrogenases.</li><li>Insect-type, or 'short-chain' alcohol dehydrogenases.</li><li>Iron-containing alcohol dehydrogenases.</li></ol>Zinc-containing ADH's [<cite idref="PUB00001354"/>, <cite idref="PUB00003420"/>] are dimeric or tetrameric enzymes that bind twoatoms of zinc per subunit. One of the zinc atom is essential for catalyticactivity while the other is not. Both zinc atoms are coordinated by eithercysteine or histidine residues; the catalytic zinc is coordinated by twocysteines and one histidine. Zinc-containing ADH's are found in bacteria,mammals, plants, and in fungi. In most species there are more than one isozyme(for example, human have at least six isozymes, yeast have three, etc.). <p>Anumber of other zinc-dependent dehydrogenases are closely related to zincADH [<cite idref="PUB00001658"/>] and are included in this family, including xylitol dehydrogenase (<db_xref db="EC" dbkey="1.1.1.9"/>); sorbitol dehydrogenase (<db_xref db="EC" dbkey="1.1.1.14"/>); aryl-alcohol dehydrogenase (<db_xref db="EC" dbkey="1.1.1.90"/>); threonine 3-dehydrogenase (<db_xref db="EC" dbkey="1.1.1.103"/>); cinnamyl-alcohol dehydrogenase (<db_xref db="EC" dbkey="1.1.1.195"/>) (CAD); galactitol-1-phosphate dehydrogenase (<db_xref db="EC" dbkey="1.1.1.251"/>); and <taxon tax_id="303">Pseudomonas putida</taxon> 5-exo-alcohol dehydrogenase (<db_xref db="EC" dbkey="1.1.1"/>).</p> Alcohol dehydrogenase, zinc-type, conserved site