5β-Reductase
5β-Reductase, or Δ4-3-oxosteroid 5β-reductase is an enzyme with systematic name 5β-cholestan-3-one:NADP+ 4,5-oxidoreductase.
This enzyme catalyses the following general chemical reaction:
For example, it interconverts 5β-dihydrocortisone and cortisone:
The human enzyme efficiently acts on progesterone, 17α-hydroxyprogesterone, androstenedione, and testosterone to transform them into 5β-reduced metabolites. It can also act on aldosterone, corticosterone, and cortisol.