Cytosolic alcohol dehydrogenase catalyzes the reaction of ethanol and NAD+ to form acetaldehyde and NADH + H+. The active form of the enzyme is a dimer with one zinc ion bound to each protein subunit. In the body, alcohol dehydrogenase is present in the liver, kidney, lung and gastric mucosa.
Six genes encode proteins active in ethanol oxidation: ADH1A, ADH1B, ADH1C, ADH4, ADH6, and ADH7 (Lange et al. 1976; Yin et al. 1985; Li et al. 1978; Bosron et al. 1979; Moreno and Pares 1991; Yokoyama et al. 1994; Chen and Yoshida 1991). ADH1A, B and C proteins can associate to form homodimers or heterodimers; ADH4, 6, and 7 proteins each form homodimers. Expression of ADH1A, B and C is developmentally regulated: ADH1A protein is abundant in the fetus, but expressed only at low levels in adulthood, when ADH1B and C proteins are abundant (Edenberg 2000). The various dimers differ substantially in the efficiency with which they oxidize ethanol. The ADH1B homodimer and heterodimers containing at least one 1B monomer are the most active towards ethanol (Yin et al. 1985). In addition, common polymorphic variants of ADH1B and C proteins differ substantially in this respect (Murray and Price 1972).