Short-chaindehydrogenases/reductases (SDRs) are enzymes of great functional diversity. Even at sequence identities of typically only 15–30%, specific sequence motifs are detect-able, reflecting common folding patterns. We have devel-oped a functional assignment scheme based on these motifs and we find five families. Two of these families were known previously and are called classical and extended families, but they are now distinguished at a further level based on coenzyme specificities.
