Last modified: Tue Jul 6 12:00:12 BST 2004

Steroid carbon nomenclature

Trivial name: Pregnenolone
Systematic name: 3ß-Hydroxypregn-5-en-20-one
Molecular formula: C21H32O2
CAS Number: 145-13-1
Merck Index (11th Ed) Number: 7739

Substrate [1]

Pathway: Pregnenolone -> 7ß-Hydroxypregnenolone
Reaction: steroid ß-hydroxylation at C7
Enzyme: P450 1A1

Substrate [2]

Pathway: Pregnenolone -> 17alpha-Hydroxypregnenolone
Reaction: steroid alpha-hydroxylation at C17
Enzyme: P450c17 (steroid 17alpha-hydroxylase/17,20-lyase), CYP17

Product [2]

Pathway: Cholesterol -> Pregnenolone + Isocaproaldehyde
Reaction: cholesterol side-chain cleavage (hydroxylation at C22 and C20 and cleavage of C20-C22 bond)
Enzyme: P450scc (cholesterol side-chain cleavage), CYP11A1


  1. Doostzadeh, J., Urban, P., Pompon, D. and Morfin, R. (1996) Pregnenolone-7ß-hydroxylating activities of yeast-expressed mouse cytochrome P450-1A1 and mouse-tissue microsomes. Eur. J. Biochem. 242, 641-647.
  2. Ruckpaul, K. and Rein, H., Eds. (1990) Frontiers in Biotransformation, vol. 3: Molecular Mechanisms of Adrenal Steroidogenesis and Aspects of Regulation and Application. Taylor & Francis, London.

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