Reaction: a Δ7-sterol + 2 ferrocytochrome b5 + O2 + 2 H+ = a Δ5,7-sterol + 2 ferricytochrome b5 + 2 H2O
For diagram of reaction click here.
Other name(s): lathosterol oxidase; Δ7-sterol Δ5-dehydrogenase; Δ7-sterol 5-desaturase; Δ7-sterol-C5(6)-desaturase; 5-DES; SC5DL (gene name); ERG3 (gene name)
Systematic name: Δ7-sterol,ferrocytochrome b5:oxygen oxidoreductase 5,6-dehydrogenating
Comments: This enzyme, found in eukaryotic organisms, catalyses the introduction of a double bond between the C5 and C6 carbons of the B ring of Δ7-sterols, to yield the corresponding Δ5,7-sterols. The enzymes from yeast, plants and vertebrates act on avenasterol, episterol, and lathosterol, respectively. The enzyme is located at the endoplasmic reticulum and is membrane bound.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Dempsey, M.E., Seaton, J.D., Schroepfer, G.J. and Trockman, R.W. The intermediary role of Δ5,7-cholestadien-3β-ol in cholesterol biosynthesis. J. Biol. Chem. 239 (1964) 1381-1387. [PMID: 14189869]
2. Honjo, K., Ishibashi, T. and Imai, Y. Partial purification and characterization of lathosterol 5-desaturase from rat liver microsomes. J. Biochem. 97 (1985) 955-959. [PMID: 4019441]
3. Arthington, B.A., Bennett, L.G., Skatrud, P.L., Guynn, C.J., Barbuch, R.J., Ulbright, C.E. and Bard, M. Cloning, disruption and sequence of the gene encoding yeast C-5 sterol desaturase. Gene 102 (1991) 39-44. [PMID: 1864507]
4. Taton, M. and Rahier, A. Plant sterol biosynthesis: identification and characterization of higher plant Δ7-sterol C5(6)-desaturase. Arch. Biochem. Biophys. 325 (1996) 279-288. [PMID: 8561508]
5. Nishino, H., Nakaya, J., Nishi, S., Kurosawa, T. and Ishibashi, T. Temperature-induced differential kinetic properties between an initial burst and the following steady state in membrane-bound enzymes: studies on lathosterol 5-desaturase. Arch. Biochem. Biophys. 339 (1997) 298-304. [PMID: 9056262]
6. Taton, M., Husselstein, T., Benveniste, P. and Rahier, A. Role of highly conserved residues in the reaction catalyzed by recombinant Δ7-sterol-C5(6)-desaturase studied by site-directed mutagenesis. Biochemistry 39 (2000) 701-711. [PMID: 10651635]
7. Poklepovich, T.J., Rinaldi, M.A., Tomazic, M.L., Favale, N.O., Turkewitz, A.P., Nudel, C.B. and Nusblat, A.D. The cytochrome b5 dependent C-5(6) sterol desaturase DES5A from the endoplasmic reticulum of Tetrahymena thermophila complements ergosterol biosynthesis mutants in Saccharomyces cerevisiae. Steroids 77 (2012) 1313-1320. [PMID: 22982564]