Class IV mammalian alcohol dehydrogenase. Structural data of the rat stomach enzyme reveal a new class well separated from those already characterized.

The stomach form of alcohol dehydrogenase has been structurally evaluated by peptide analysis covering six separate regions of the rat enzyme. Overall, this new structure differs widely (32-40% residue differences) from the structures of three classes of alcohol dehydrogenase characterized before from the same species. Consequently, this novel enzyme constitutes a true fourth class of mammalian alcohol dehydrogenase. In particular, differences are extensive also towards class II, although enzymatic and physicochemical properties initially suggested overall similarities with class II. The new structure establishes the presence of one further alcohol dehydrogenase mammalian gene, extends the enzyme family derived from repeated gene duplications, and confirms tissue-specific expressions.