Accepted name: Δ7-sterol 5(6)-desaturase
Reaction: a Δ7-sterol + 2 ferrocytochrome b5 + O2 + 2 H+ = a Δ5,7-sterol + 2 ferricytochrome b5 + 2 H2O
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.
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]
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