Steroid 5α-reductase (5α-reductase (SRD5A))

Steroid 5α-reductase is a membrane-embedded, NADPH-dependent enzyme family that catalyzes the irreversible reduction of Δ⁴,⁵ double bonds in 3-keto steroids, most notably the conversion of testosterone to the much more potent androgen dihydrotestosterone (DHT)[1][5][4][6]. In humans, several isoforms exist (SRD5A1, SRD5A2, SRD5A3), which differ in tissue distribution, substrate preference, and physiological role. Aberrant activity or genetic deficiency of these enzymes is implicated in disorders of sexual development, androgenic alopecia, prostate diseases, and may play roles in neuropsychiatric disorders due to effects on neurosteroids[3][4][6]. 5α-reductase inhibitors, such as finasteride and dutasteride, are widely used therapeutically, though treatment is limited by potential endocrine and neurological side effects[3][9][6]. Note: For proper structured data in databases, each isozyme (e.g., "Steroid 5α-reductase type 2" for SRD5A2) should ideally be listed separately, as their disease relevance, tissue expression, and inhibitor selectivity may differ[1][4][5][6].

Other names

5α-reductase3-oxo-5α-steroid 4-dehydrogenase3-oxosteroid Δ⁴-dehydrogenaseTestosterone 5α-reductaseSRD5A

Competitive inhibition of testosterone binding/conversion to DHT (for anti-androgenic drugs); Inhibitor occupies catalytic site, blocking NADPH-mediated reduction; Some inhibitors are mechanism-based, forming stable enzyme-inhibitor complexes.