The role and mechanism of microbial 3-ketosteroid Delta(1) -dehydrogenases in steroid breakdown

3-Ketosteroid Delta(1)-dehydrogenases are FAD-dependent enzymes that catalyze the introduction of a double bond between the Cl and C2 atoms of the A-ring of 3-ketosteroid substrates. These enzymes are found in a large variety of microorganisms, especially in bacteria belonging to the phylum Actinobacteria. They play a critical role in the early steps of the degradation of the steroid core. 3-Ketosteroid Delta(1)-dehydrogenases are of particular interest for the etiology of some infectious diseases, for the production of starting materials for the pharmaceutical industry, and for environmental bioremediation applications. Here we summarize and discuss the biochemical and enzymological properties of these enzymes, their microbial sources, and their natural diversity. The three-dimensional structure of a 3-ketosteroid Delta(1)-dehydrogenase in connection with the enzyme mechanism is highlighted.