Figure 1.

Biosynthesis of neurosteroids. 5α-DHP, 5α-dehydroprogesterone; ALLO, 3α-hydroxy, 5α-pregnane-20-one; 3α5α20α-HHP, 3α,5α,20α-hexahydroprogesterone; P450_scc, cytochrome P₄₅₀ side chain cleavage; 3β-HSD, 3β-hydroxysteroid dehydrogenase; 3α-HSOR^C, 3α-hydroxysteroid oxidoreductase cytosolic (K_m for 5αDHP, 80 nM; K_m for ALLO, 2 μM; NADPH/NADP⁺ linked); 3α-HSOR^P, 3α-hydroxysteroid oxidoreductase particulate (K_m for 5α-DHP, 230 nM; K_m for ALLO, 58 nM; NADH/NAD⁺-linked); 20α-HSOR, 20α-hydroxysteroidoxydoreductase. The kinetic properties of 3α-HSOR^C and 3α-HSOR^P are from Karavolas and Hodges (8).