<P> The active site of human ADH1 (PDB: 1HSO) consists of a zinc atom, His - 67, Cys - 174, Cys - 46, Thr - 48, His - 51, Ile - 269, Val - 292, Ala - 317, and Leu - 319 . In the commonly studied horse liver isoform, Thr - 48 is a Ser, and Leu - 319 is a Phe . The zinc coordinates the substrate (alcohol). The zinc is coordinated by Cys - 46, Cys - 174, and His - 67 . Leu - 319, Ala - 317, His - 51, Ile - 269 and Val - 292 stabilize NAD by forming hydrogen bonds . His - 51 and Ile - 269 form hydrogen bonds with the alcohols on nicotinamide ribose . Phe - 319, Ala - 317 and Val - 292 form hydrogen bonds with the amide on NAD . </P> <P> Mammalian alcohol dehydrogenases also have a structural zinc site . This Zn ion plays a structural role and is crucial for protein stability . The structures of the catalytic and structural zinc sites in horse liver alcohol dehydrogenase (HLADH) as revealed in crystallographic structures, which has been studied computationally with quantum chemical as well as with classical molecular dynamics methods . The structural zinc site is composed of four closely spaced cysteine ligands (Cys97, Cys100, Cys103, and Cys111 in the amino acid sequence) positioned in an almost symmetric tetrahedron around the Zn ion . A recent study showed that the interaction between zinc and cysteine is governed by primarily an electrostatic contribution with an additional covalent contribution to the binding . </P> <P> In humans, ADH exists in multiple forms as a dimer and is encoded by at least seven different genes . There are five classes (I-V) of alcohol dehydrogenase, but the hepatic form that is used primarily in humans is class 1 . Class 1 consists of α, β, and γ subunits that are encoded by the genes ADH1A, ADH1B, and ADH1C . The enzyme is present at high levels in the liver and the lining of the stomach . It catalyzes the oxidation of ethanol to acetaldehyde (ethanal): </P> <Dl> <Dd> CH CH OH + NAD → CH CHO + NADH + H </Dd> </Dl>

Where is alcohol dehydrogenase found in the body