IntEnz

EC 1.14.15.6 - Cholesterol monooxygenase (side-chain-cleaving)

IntEnz Enzyme Nomenclature
EC 1.14.15.6

Names

Reactions

• (1) cholesterol + 6 reduced adrenodoxin + 3 O2 + 6 H+ = pregnenolone + 4-methylpentanal + 6 oxidized adrenodoxin + 4 H2O
•   (1a) cholesterol + 2 reduced adrenodoxin + O2 + 2 H+ = (22R)-22-hydroxycholesterol + 2 oxidized adrenodoxin + H2O
•   (1b) (22R)-22-hydroxycholesterol + 2 reduced adrenodoxin + O2 + 2 H+ = (20R,22R)-20,22-dihydroxycholesterol + 2 oxidized adrenodoxin + H2O
•   (1c) (20R,22R)-20,22-dihydroxy-cholesterol + 2 reduced adrenodoxin + O2 + 2 H+ = pregnenolone + 4-methylpentanal + 2 oxidized adrenodoxin + 2 H2O

Cofactor

• heme-thiolate

Comments:

A heme-thiolate protein (cytochrome P450). The reaction proceeds in three stages, with two hydroxylations at C-22 and C-20 preceding scission of the side-chain between carbons 20 and 22. The initial source of the electrons is NADPH, which transfers the electrons to the adrenodoxin via EC 1.18.1.6, adrenodoxin-NADP+ reductase.

Links to other databases

References

1. Burstein, S., Middleditch, B. S., Gut, M.
   Mass spectrometric study of the enzymatic conversion of cholesterol to (22R)-22-hydroxycholesterol, (20R,22R)-20,22-dihydroxycholesterol, and pregnenolone, and of (22R)-22-hydroxycholesterol to the lgycol and pregnenolone in bovine adrenocortical preparations. Mode of oxygen incorporation.
   J. Biol. Chem. 250 : 9028-9037 (1975). [PMID: 1238395]
2. Hanukoglu, I., Spitsberg, V., Bumpus, J. A., Dus, K. M., Jefcoate, C. R.
   Adrenal mitochondrial cytochrome P-450scc. Cholesterol and adrenodoxin interactions at equilibrium and during turnover.
   J. Biol. Chem. 256 : 4321-4328 (1981). [PMID: 7217084]
3. Hanukoglu, I., Hanukoglu, Z.
   Stoichiometry of mitochondrial cytochromes P-450, adrenodoxin and adrenodoxin reductase in adrenal cortex and corpus luteum. Implications for membrane organization and gene regulation.
   Eur. J. Biochem. 157 : 27-31 (1986). [PMID: 3011431]
4. Strushkevich, N., MacKenzie, F., Cherkesova, T., Grabovec, I., Usanov, S., Park, H. W.
   Structural basis for pregnenolone biosynthesis by the mitochondrial monooxygenase system.
   Proc. Natl. Acad. Sci. U.S.A. 108 : 10139-10143 (2011). [PMID: 21636783]
5. Mast, N., Annalora, A. J., Lodowski, D. T., Palczewski, K., Stout, C. D., Pikuleva, I. A.
   Structural basis for three-step sequential catalysis by the cholesterol side chain cleavage enzyme CYP11A1.
   J. Biol. Chem. 286 : 5607-5613 (2011). [PMID: 21159775]

[EC 1.14.15.6 created 1983, modified 2013, modified 2014]