5α-reductase

5α-reductase is a family of enzymes that converts testosterone into dihydrotestosterone by reducing the steroid’s Δ4,5 double bond. Its three human isoenzymes differ in tissue distribution and biochemical properties.

Dihydrotestosterone: A potent androgen formed from testosterone by reduction of its Δ4,5 double bond. It is the direct product of the reaction catalyzed by 5α-reductase.
Finasteride: A medication that inhibits type 2 and, at higher doses, type 1 5α-reductase. It reduces dihydrotestosterone production to treat benign prostatic hyperplasia and pattern hair loss.
Steroid: A class of lipids built around a four-ring carbon skeleton, including hormones and membrane components. Testosterone and dihydrotestosterone are steroids with a shared four-ring structure.
External genital development: The formation of external reproductive structures during embryonic and fetal development. Dihydrotestosterone produced by 5α-reductase is required for typical masculinization of external genitalia.
Testosterone: A steroid hormone that supports reproductive development and serves as a precursor to dihydrotestosterone and estradiol. It supplies the substrate that 5α-reductase converts into dihydrotestosterone.
Dutasteride: A medication that inhibits both type 1 and type 2 5α-reductase. Its dual inhibition lowers dihydrotestosterone more broadly than finasteride.
Oxidoreductase: An enzyme class that catalyzes electron-transfer reactions between molecules. 5α-reductase belongs to this broad enzyme class because its reaction reduces a carbon-carbon double bond.
Prostate: A gland beneath the bladder that contributes fluid to semen and is responsive to androgens. Local conversion of testosterone supplies dihydrotestosterone that supports prostate development and growth.
SRD5A1: A gene encoding the type 1 isoenzyme of steroid 5α-reductase. Its enzyme product is one of the three human 5α-reductase isoenzymes.
Benign prostatic hyperplasia: A noncancerous enlargement of the prostate that can obstruct urine flow. 5α-reductase inhibitors can shrink the prostate by reducing local dihydrotestosterone.

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