3β-Hydroxysteroid dehydrogenase/Δ5-4 isomerase (3β-HSD) (EC 1.1.1.145) is an enzyme that catalyzes the biosynthesis of the steroid progesterone from pregnenolone, 17α-hydroxyprogesterone from 17α-hydroxypregnenolone, and androstenedione from dehydroepiandrosterone (DHEA) in the adrenal gland.
3β-HSD is also known as delta Δ5-4-isomerase, which catalyzes the oxidative conversion of Δ5-3β-hydroxysteroids to the Δ4-3-keto configuration and is, therefore, essential for the biosynthesis of all classes of hormonal steroids, namely progesterone, glucocorticoids, mineralocorticoids, androgens, and estrogens.
[2] The 3β-HSD complex is responsible for the conversion of: 3β-HSD belongs to the family of oxidoreductases, to be specific, those acting on the CH-OH group with NAD+ or NADP+ as acceptor.
The fetal adrenal cortex lacks expression of the enzyme early on, thus mineralocorticoids (e.g. aldosterone) and glucocorticoids (e.g. cortisol) cannot be synthesized.
This is significant because cortisol induces type II pneumocytes of the lungs to synthesize and secrete pulmonary surfactant; without pulmonary surfactant to reduce the alveolar surface tension, premature neonates may die of neonatal respiratory distress syndrome.