Steroid 5-alpha-reductase enzyme (5α-reductase)

Steroid 5-alpha-reductase enzyme is a family of membrane-bound oxidoreductase enzymes that catalyze the irreversible reduction of the Δ⁴,⁵ double bond in 3-oxo (3-keto) C19 or C21 steroids, converting testosterone into the more potent androgen dihydrotestosterone (DHT) using NADPH as a cofactor[1][5]. There are three main human isozymes (types 1, 2, and 3) encoded by SRD5A1, SRD5A2, and SRD5A3 genes, each with distinctive tissue distributions and roles[1][4][5]. Type 2 is critical in male sexual differentiation and external genital development, and its deficiency causes 5-alpha-reductase deficiency. Inhibition of these enzymes is a validated therapeutic approach in prostate disorders (BPH, cancer), androgenetic alopecia, and hirsutism, with finasteride and dutasteride being principal drugs[7]. The enzyme is expressed in the skin, prostate, reproductive organs, liver, and nervous system[5]. Safety concerns for inhibitors include sexual dysfunction, fertility effects, and potential teratogenic risk.

Other names

3-oxo-5α-steroid 4-dehydrogenase5-alpha-reductase5α-RSRD5A (gene family abbreviation)Steroid 5α-reductase isoenzyme 1 (SRD5A1)Steroid 5α-reductase isoenzyme 2 (SRD5A2)Steroid 5α-reductase isoenzyme 3 (SRD5A3)

Enzyme inhibition (prevents conversion of testosterone to DHT) Selective blockade (Type 1, Type 2, or both isoenzymes, depending on the drug)