5β-Reductase

5β-Reductase, or Δ⁴-3-oxosteroid 5β-reductase (EC 1.3.1.3, 3-oxo-Δ⁴-steroid 5β-reductase, androstenedione 5β-reductase, cholestenone 5β-reductase, cortisone 5β-reductase, cortisone Δ⁴-5β-reductase, steroid 5β-reductase, testosterone 5β-reductase, Δ⁴-3-ketosteroid 5β-reductase, Δ⁴-5β-reductase, Δ⁴-hydrogenase, 4,5β-dihydrocortisone:NADP⁺ Δ⁴-oxidoreductase, 3-oxo-5β-steroid:NADP⁺ Δ⁴-oxidoreductase) is an enzyme with systematic name 5β-cholestan-3-one:NADP⁺ 4,5-oxidoreductase.^{[1][2][3][4][5][6][7][8]}

This enzyme catalyses the following general chemical reaction:

5β-cholestan-3-one + NADP⁺ ${\displaystyle \rightleftharpoons }$ cholest-4-en-3-one + NADPH + H⁺

For example, it interconverts 5β-dihydrocortisone and cortisone:^[9][10]

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.^[9]