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allopregnanolone biosynthesis

General Background : 3-BETA-HYDROXY-5-ALPHA-PREGNANE-20-ONE is a neuroactive steroid which is a steroid that is able to regulate neural functions. It is derived from : PROGESTERONE and is synthesized within the nervous tissue . Contrary to : PROGESTERONE and its first metabolite dihydroprogesterone (: CPD-293), : 3-BETA-HYDROXY-5-ALPHA-PREGNANE-20-ONE is able to interact with GABA-A receptor and not with the classical progesterone receptor . About This Pathway This pathway consists in a two step reduction of : PROGESTERONE. In the first step : PROGESTERONE is reduced to its first metabolite dihydroprogesterone by the enzyme 5alpha-reductase. The second step, in which dihydroprogesterone is reduced to : 3-BETA-HYDROXY-5-ALPHA-PREGNANE-20-ONE, is catalyzed by enzymes showing a 3alpha-hydroxysteroid oxidoreductase activity. In humans there are four isoforms: : HS10741, : HS07754, : HS03054, : HS10739. These isoforms display broad specificity for steroid substrates and hence their physiological role in steroid metabolism is influenced by their tissue distribution . : HS07754 is the most implicated in : 3-BETA-HYDROXY-5-ALPHA-PREGNANE-20-ONE formation. The back-oxidation of : 3-BETA-HYDROXY-5-ALPHA-PREGNANE-20-ONE to : CPD-293 is catalyzed by a NAD-dependent 3alpha-hydroxysteroid dehydrogenase : HS01113 .

from BIOCYC source record: HUMAN_PWY-7455
Type: pathway
Taxonomic scope
organism-specific biosystem
Homo sapiens

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