5beta-cholestane-3alpha,7alpha-diol 12alpha-hydroxylase

The 4 substrates of this enzyme are 5beta-cholestane-3alpha,7alpha-diol, NADPH, H⁺, and O₂, whereas its 3 products are 5beta-cholestane-3alpha,7alpha,12alpha-triol, NADP⁺, and H₂O.

This enzyme 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 NADH or NADPH as one donor, and incorporation of one atom o oxygen into the other donor. The systematic name of this enzyme class is 5beta-cholestane-3alpha,7alpha-diol,NADPH:oxygen oxidoreductase (12alpha-hydroxylating). Other names in common use include 5beta-cholestane-3alpha,7alpha-diol 12alpha-monooxygenase, sterol 12alpha-hydroxylase (ambiguous), CYP8B1, and cytochrome P450 8B1.

References

Hansson R; Wikvall K (1982). "Hydroxylations in biosynthesis of bile acids. Cytochrome P-450 LM4 and 12alpha-hydroxylation of 5beta-cholestane-3alpha, 7alpha-diol". Eur. J. Biochem. 125 (2): 423–9. doi:10.1111/j.1432-1033.1982.tb06700.x. PMID 6811268.
Hansson R; Wikvall K (1980). "Hydroxylations in biosynthesis and metabolism of bile acids Catalytic properties of different forms of cytochrome P-450". J. Biol. Chem. 255 (4): 1643–9. PMID 6766451.
Lundell K; Wikvall K (2003). "Gene structure of pig sterol 12alpha-hydroxylase (CYP8B1) and expression in fetal liver: comparison with expression of taurochenodeoxycholic acid 6alpha-hydroxylase (CYP4A21)". Biochim. Biophys. Acta. 1634 (3): 86–96. doi:10.1016/j.bbalip.2003.09.002. PMID 14643796.
G, Martens S; Matern, U; Junghanns, KT; Heskamp, ML; Britsch, L; Forkmann, G; Martens, S (2001). "Purification and antigenicity of flavone synthase I from irradiated parsley cells". Arch. Biochem. Biophys. 393 (1): 177–83. doi:10.1006/abbi.2001.2491. PMID 11516175.
Yang Y; Zhang M; Eggertsen G; Chiang JY (2002). "On the mechanism of bile acid inhibition of rat sterol 12alpha-hydroxylase gene (CYP8B1) transcription: roles of alpha-fetoprotein transcription factor and hepatocyte nuclear factor 4alpha". Biochim. Biophys. Acta. 1583 (1): 63–73. doi:10.1016/s1388-1981(02)00186-5. PMID 12069850.
Russell DW (2003). "The enzymes, regulation, and genetics of bile acid synthesis". Annu. Rev. Biochem. 72 (1): 137–74. doi:10.1146/annurev.biochem.72.121801.161712. PMID 12543708.

Oxidoreductases: dioxygenases, including steroid hydroxylases (EC 1.14)

1.14.11: 2-oxoglutarate	Prolyl hydroxylase Lysyl hydroxylase

1.14.13: NADH or NADPH	Flavin-containing monooxygenase FMO1 FMO2 FMO3 FMO4 FMO5 Nitric oxide synthase NOS1 NOS2 NOS3 Cholesterol 7 alpha-hydroxylase Methane monooxygenase 3A4 Lanosterol 14 alpha-demethylase 24-hydroxycholesterol 7α-hydroxylase

1.14.14: reduced flavin or flavoprotein	19A1 2D6 2E1

1.14.15: reduced iron-sulfur protein	11B1 11B2 11A1

1.14.16: reduced pteridine (BH4 dependent)	Phenylalanine hydroxylase Tyrosine hydroxylase Tryptophan hydroxylase

1.14.17: reduced ascorbate	Dopamine beta-hydroxylase

1.14.18-19: other	Tyrosinase Stearoyl-CoA desaturase-1

1.14.99 - miscellaneous	Cyclooxygenase Heme oxygenase (HMOX1) Squalene monooxygenase 17A1 21A2

Enzymes

Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Catalytically perfect enzyme Coenzyme Cofactor Enzyme catalysis Enzyme kinetics Lineweaver–Burk plot Michaelis–Menten kinetics

Regulation	Allosteric regulation Cooperativity Enzyme inhibitor

Classification	EC number Enzyme superfamily Enzyme family List of enzymes

Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list)

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