The short-chain dehydrogenases/reductases family (SDR) [<cite idref="PUB00000419"/>] is a very large family of enzymes, most of which are known to be NAD- or NADP-dependent oxidoreductases. As the first member of this family to be characterised was Drosophila alcohol dehydrogenase, this family used to be called [<cite idref="PUB00001371"/>, <cite idref="PUB00001399"/>, <cite idref="PUB00001408"/>] 'insect-type', or 'short-chain' alcohol dehydrogenases. Most member of this family are proteins of about 250 to 300 amino acid residues. Most dehydrogenases possess at least 2 domains [<cite idref="PUB00004592"/>], the first binding the coenzyme, often NAD, and the second binding the substrate. This latter domain determines the substrate specificity and contains amino acids involved in catalysis. Little sequence similarity has been found in the coenzyme binding domain although there is a large degree of structural similarity, and it has therefore been suggested that the structure of dehydrogenases has arisen through gene fusion of a common ancestral coenzyme nucleotide sequence with various substrate specific domains [<cite idref="PUB00004592"/>].