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In enzymology, a Δ⁷-sterol 5(6)-desaturase ( EC 1.14.19.20) is an enzyme that catalyzes the chemical reaction

Δ⁷-sterol + 2 ferrocytochrome b₅ + O₂ + 2 H⁺ = Δ^5,7-sterol + 2 ferricytochrome b₅ + 2 H₂O

The four substrates of this enzyme are Δ⁷-sterol, ferrocytochrome b₅, H⁺, and O₂. Its three products are Δ^5,7-sterol, ferricytochrome b₅, and H₂O.

Classification

This enzyme is one of C-5 sterol desaturases, belongs to the family of oxidoreductases, specifically those acting on paired donors, with O₂ as oxidant and incorporation or reduction of oxygen. The oxygen incorporated need not be derived from O₂. With oxidation of a pair of donors resulting in the reduction of molecular oxygen to two molecules of water.

Nomenclature

The systematic name of this enzyme class is Δ⁷-sterol,ferrocytochrome b5:oxygen oxidoreductase 5,6-dehydrogenating. Other names in common use include:

• lathosterol oxidase
• Δ⁷-sterol Δ⁵-dehydrogenase
• Δ⁷-sterol 5-desaturase
• Δ⁷-sterol-C5(6)-desaturase
• 5-DES

Gene names:

• SC5D (vertebrates)
• ERG3 (yeast)

Biological role

This enzyme participates in biosynthesis of steroids.

History

Previously, this enzyme was known under the name lathosterol oxidase and ( EC 1.14.21.6), and the entry is now transferred. The following incorrect reaction was suggested:

5α-cholest-7-en-3β-ol + NAD(P)H + H⁺ + O₂ ${\displaystyle \rightleftharpoons }$ cholesta-5,7-dien-3β-ol + NAD(P)+ + 2 H₂O

The substrates of this enzyme were listed as 5α-cholest-7-en-3β-ol, NAD(P)H, H⁺, and O₂. Its products were listed as cholesta-5,7-dien-3β-ol (provitamin D₃), NAD⁺ or NADP⁺, and H₂O. It was stated that the enzyme has two cofactors: FAD, and FMN.

See also

• Fatty acid desaturase
• C-5 sterol desaturase

References

• Dempsey ME, Seaton JD, Schroepfer GJ, Trockman RW (1964). "The Intermediary Role of Δ^5,7-cholestadien-3-β-ol in Cholesterol Biosynthesis". J. Biol. Chem. 239: 1381–7. PMID  14189869.
• Nishino H, Nakaya J, Nishi S, Kurosawa T, Ishibashi T (1997). "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 (2): 298–304. doi: 10.1006/abbi.1996.9871. PMID  9056262.
• Taton M, Rahier A (1996). "Plant sterol biosynthesis: identification and characterization of higher plant Δ⁷-sterol C5(6)-desaturase". Arch. Biochem. Biophys. 325 (2): 279–88. doi: 10.1006/abbi.1996.0035. PMID  8561508.
• Taton M, Husselstein T, Benveniste P, Rahier A (2000). "Role of highly conserved residues in the reaction catalyzed by recombinant Δ⁷-sterol-C5(6)-desaturase studied by site-directed mutagenesis". Biochemistry. 39 (4): 701–11. doi: 10.1021/bi991467t. PMID  10651635.