Methylsterol monooxygenase

{{Short description|Class of enzymes}}

{{Infobox enzyme

| Name = Methylsterol monooxygenase

| EC_number = 1.14.13.72

| CAS_number = 37256-80-7

| GO_code =

| image =

| width =

| caption =

}}

Methylsterol monooxygenase ({{EC number|1.14.13.72}}, methylsterol hydroxylase, 4-methylsterol oxidase, 4,4-dimethyl-5alpha-cholest-7-en-3beta-ol,hydrogen-donor:oxygen oxidoreductase (hydroxylating)) is an enzyme with systematic name 4,4-dimethyl-5alpha-cholest-7-en-3beta-ol,NAD(P)H:oxygen oxidoreductase (hydroxylating).{{cite journal | vauthors = Rahier A, Smith M, Taton M | title = The role of cytochrome b5 in 4alpha-methyl-oxidation and C5(6) desaturation of plant sterol precursors | journal = Biochemical and Biophysical Research Communications | volume = 236 | issue = 2 | pages = 434–7 | date = July 1997 | pmid = 9240456 | doi = 10.1006/bbrc.1997.6974 }}{{cite journal | vauthors = Pascal S, Taton M, Rahier A | title = Plant sterol biosynthesis. Identification and characterization of two distinct microsomal oxidative enzymatic systems involved in sterol C4-demethylation | journal = The Journal of Biological Chemistry | volume = 268 | issue = 16 | pages = 11639–54 | date = June 1993 | pmid = 8505296 }}{{cite journal | vauthors = Kawata S, Trzaskos JM, Gaylor JL | title = Affinity chromatography of microsomal enzymes on immobilized detergent-solubilized cytochrome b5 | journal = The Journal of Biological Chemistry | volume = 261 | issue = 8 | pages = 3790–9 | date = March 1986 | pmid = 3949790 }}{{cite journal | vauthors = Fukushima H, Grinstead GF, Gaylor JL | title = Total enzymic synthesis of cholesterol from lanosterol. Cytochrome b5-dependence of 4-methyl sterol oxidase | journal = The Journal of Biological Chemistry | volume = 256 | issue = 10 | pages = 4822–6 | date = May 1981 | pmid = 7228857 }}{{cite journal | vauthors = Brady DR, Crowder RD, Hayes WJ | title = Mixed function oxidases in sterol metabolism. Source of reducing equivalents | journal = The Journal of Biological Chemistry | volume = 255 | issue = 22 | pages = 10624–9 | date = November 1980 | pmid = 7430141 }}{{cite journal | vauthors = Gaylor JL, Mason HS | title = Investigation of the component reactions of oxidative sterol demethylation. Evidence against participation of cytochrome P-450 | journal = The Journal of Biological Chemistry | volume = 243 | issue = 19 | pages = 4966–72 | date = October 1968 | pmid = 4234469 }}{{cite journal | vauthors = Miller WL, Kalafer ME, Gaylor JL, Delwiche CV | title = Investigation of the component reactions of oxidative sterol demethylation. Study of the aerobic and anaerobic processes | journal = Biochemistry | volume = 6 | issue = 9 | pages = 2673–8 | date = September 1967 | pmid = 4383278 | doi = 10.1021/bi00861a005 }} This enzyme catalyses the following chemical reaction

: 4,4-dimethyl-5alpha-cholest-7-en-3beta-ol + 3 NAD(P)H + 3 H⁺ + 3 O₂ $\backslash rightleftharpoons$ 3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carboxylate + 3 NAD(P)⁺ + 4 H₂O (overall reaction)

:(1a) 4,4-dimethyl-5alpha-cholest-7-en-3beta-ol + NAD(P)H + H⁺ + O₂ $\backslash rightleftharpoons$ 4beta-hydroxymethyl-4alpha-methyl-5alpha-cholest-7-en-3beta-ol + NAD(P)⁺ + H₂O

:(1b) 4beta-hydroxymethyl-4alpha-methyl-5alpha-cholest-7-en-3beta-ol + NAD(P)H + H⁺ + O₂ $\backslash rightleftharpoons$ 3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carbaldehyde + NAD(P)⁺ + 2 H₂O

:(1c) 3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carbaldehyde + NAD(P)H + H⁺ + O₂ $\backslash rightleftharpoons$ 3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carboxylate + NAD(P)⁺ + H₂O

Methylsterol monooxygenase requires cytochrome b5.