5-alpha reductase

5-alpha reductase is an enzyme involved in steroid metabolism.

Function
It converts testosterone, the male sex hormone, into the more potent dihydrotestosterone:

Note the major difference &mdash; the Δ4,5 double-bond on the A (leftmost) ring. (The other differences between the diagrams are unrelated to chemical structure.)

Isoenzymes
There are two isoenzymes, steroid 5-alpha reductase 1 and 2 (SRD5A1 and SRD5A2).

The second isoenzyme is deficient in 5-alpha-reductase deficiency which leads to a form of intersexualism.

Production and inhibition
The enzyme is produced only in specific tissues of the male human body, namely the skin, seminal vesicles, prostate and epididymis.

Inhibition of 5-alpha reductase results in decreased production of DHT, increased levels of testosterone and possibly increased levels of estradiol. Gynecomastia is a possible side effect of 5-alpha reductase inhibition.

Pharmacology
5-alpha-reductase inhibitor drugs are used in benign prostatic hyperplasia, prostate cancer and baldness. both isoforms are also produced in the brain, where they serve to create the neurosteroid Allopregnenolone (5AR type I) and convert T to DHT(5AR type II)(1). Finasteride inhibits the function of only one of the isoenzymes (type 2), while dutasteride inhibits both forms.

Research has indicated certain mushrooms have anti-5-alpha reductase activity.