The human alcohol dehydrogenase (ADH) family of proteins catalyzes the reversible oxidation of a wide range of alcohols, including beverage alcohol. ADHs are dimers of 40 kDa subunits with a zinc ion in the active site; they use NAD as the coenzyme in catalysis (Hurley et al., 2003). In humans, there are seven isozymes with different electrophoretic and kinetic properties, but overlapping substrate specificities (Edenberg and Bosron, 1997). The isozymes are encoded by seven genes, ADH1A, ADH1B, ADH1C, ADH4, ADH5, ADH6 and ADH7, present as a cluster spanning approximately 365 kb on chromosome 4q23 (Figure 1A). All except ADH7 are expressed in liver (Edenberg, 2000). The class I isozymes ADH1A, ADH1B and ADH1C account for approximately 70% of alcohol metabolism in the liver, with ADH4 contributing most of the remaining 30% (Hurley et al., 2003).
