Multifunctionality of human 17β-hydroxysteroid dehydrogenases

17β-Hydroxysteroid dehydrogenases (17β-HSDs) belong to the family of short chain dehydrogenases/reductases (SDRs) and aldoketo-reductases (AKRs). Some of the enzymes were discovered and named due to their enzymatic activity on steroid substrates or according to their sequence homology to other 17β-HSDs. During characterisation of these enzymes it turned out that their substrate specificity is broader than first expected and key functions of some 17β-HSDs in vivo are probably not in steroid metabolism but in basic metabolic pathways. The issue of such multifunctionality is the topic of this review.