3-Oxo-5α-steroid 4-dehydrogenase 1 (SRD5A1)

**3-Oxo-5α-steroid 4-dehydrogenase 1** (commonly known as steroid 5α-reductase type 1, encoded by the SRD5A1 gene) is a membrane-bound oxidoreductase enzyme that catalyzes the NADPH-dependent reduction of the Δ4,5 double bond in 3-oxo (3-keto) steroid substrates, such as testosterone, converting them into their more potent 5α-dihydro derivatives, like dihydrotestosterone (DHT)[1][2]. It plays a critical role in androgen and estrogen metabolism, bile acid biosynthesis, and the production of various neuroactive steroids that modulate GABAergic signaling[1][2]. SRD5A1 is expressed in many tissues and, along with SRD5A2, has been implicated as a therapeutic target, particularly in the context of hormone-dependent diseases such as prostate cancer and benign prostatic hyperplasia[3]. Clinically used inhibitors like dutasteride and finasteride act on SRD5A1/2 to reduce DHT production as a therapeutic strategy. Distinct roles for SRD5A1 in certain cancers and potential influences on neurophysiology underscore its biomedical importance[2][3].

Other names

Steroid 5α-reductase type 15α-reductase type 1Steroid-5-alpha-reductase, alpha polypeptide 1

Inhibition of enzyme activity to reduce DHT synthesis[3]; Competitive and noncompetitive binding to the steroid substrate binding pocket or NADPH site[3]