The Enzyme Database

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Accepted name: microsomal epoxide hydrolase
Reaction: (1) cis-stilbene oxide + H2O = (1R,2R)-1,2-diphenylethane-1,2-diol
(2) 1-(4-methoxyphenyl)-N-methyl-N-[(3-methyloxetan-3-yl)methyl]methanamine + H2O = 2-({[(4-methoxyphenyl)methyl](methyl)amino}methyl)-2-methylpropane-1,3-diol
Glossary: oxirane = ethylene oxide = a 3-membered oxygen-containing ring
oxetane = 1,3-propylene oxide = a 4-membered oxygen-containing ring
Other name(s): microsomal oxirane/oxetane hydrolase; epoxide hydratase (ambiguous); microsomal epoxide hydratase (ambiguous); epoxide hydrase; microsomal epoxide hydrase; arene-oxide hydratase (ambiguous); benzo[a]pyrene-4,5-oxide hydratase; benzo(a)pyrene-4,5-epoxide hydratase; aryl epoxide hydrase (ambiguous); cis-epoxide hydrolase; mEH; EPHX1 (gene name)
Systematic name: cis-stilbene-oxide hydrolase
Comments: This is a key hepatic enzyme that catalyses the hydrolytic ring opening of oxiranes (epoxides) and oxetanes to give the corresponding diols. The enzyme is involved in the metabolism of numerous substrates including the stereoselective hydrolytic ring opening of 7-oxabicyclo[4.1.0]hepta-2,4-dienes (arene oxides) to the corresponding trans-dihydrodiols. The reaction proceeds via a triad mechanism and involves the formation of an hydroxyalkyl-enzyme intermediate. Five epoxide-hydrolase enzymes have been identified in vertebrates to date: EC (leukotriene-A4 hydrolase), EC (hepoxilin-epoxide hydrolase), EC (microsomal epoxide hydrolase), EC (soluble epoxide hydrolase) and EC (cholesterol-5,6-oxide hydrolase).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Oesch, F. and Daly, J. Solubilization, purification, and properties of a hepatic epoxide hydrase. Biochim. Biophys. Acta 227 (1971) 692–697. [DOI] [PMID: 4998715]
2.  Jakoby, W.B. and Fjellstedt, T.A. Epoxidases. In: Boyer, P.D. (Ed.), The Enzymes, 3rd edn, vol. 7, Academic Press, New York, 1972, pp. 199–212.
3.  Oesch, F. Mammalian epoxide hydrases: inducible enzymes catalysing the inactivation of carcinogenic and cytotoxic metabolites derived from aromatic and olefinic compounds. Xenobiotica 3 (1973) 305–340. [DOI] [PMID: 4584115]
4.  Oesch, F. Purification and specificity of a human microsomal epoxide hydratase. Biochem. J. 139 (1974) 77–88. [PMID: 4463951]
5.  Lu, A.Y., Ryan, D., Jerina, D.M., Daly, J.W. and Levin, W. Liver microsomal expoxide hydrase. Solubilization, purification, and characterization. J. Biol. Chem. 250 (1975) 8283–8288. [PMID: 240858]
6.  Bellucci, G., Chiappe, C. and Ingrosso, G. Kinetics and stereochemistry of the microsomal epoxide hydrolase-catalyzed hydrolysis of cis-stilbene oxides. Chirality 6 (1994) 577–582. [DOI] [PMID: 7986671]
7.  Fretland, A.J. and Omiecinski, C.J. Epoxide hydrolases: biochemistry and molecular biology. Chem. Biol. Interact. 129 (2000) 41–59. [DOI] [PMID: 11154734]
8.  Morisseau, C. and Hammock, B.D. Epoxide hydrolases: mechanisms, inhibitor designs, and biological roles. Annu. Rev. Pharmacol. Toxicol. 45 (2005) 311–333. [DOI] [PMID: 15822179]
9.  Newman, J.W., Morisseau, C. and Hammock, B.D. Epoxide hydrolases: their roles and interactions with lipid metabolism. Prog. Lipid Res. 44 (2005) 1–51. [DOI] [PMID: 15748653]
10.  Toselli, F., Fredenwall, M., Svensson, P., Li, X.Q., Johansson, A., Weidolf, L. and Hayes, M.A. Oxetane substrates of human microsomal epoxide hydrolase. Drug Metab. Dispos. 45 (2017) 966–973. [DOI] [PMID: 28600384]
[EC created 2006 (EC created 1978, modified 1999, part incorporated 2006), modified 2017]
Accepted name: (6-4)DNA photolyase
Reaction: (6-4) photoproduct (in DNA) = 2 pyrimidine residues (in DNA)
For diagram click here
Other name(s): DNA photolyase; H64PRH; NF-10; phr (6-4); PL-(6-4); OtCPF1; (6-4) PHR; At64PHR
Systematic name: (6-4) photoproduct pyrimidine-lyase
Comments: A flavoprotein (FAD). The overall repair reaction consists of two distinct steps, one of which is light-independent and the other one light-dependent. In the initial light-independent step, a 6-iminium ion is thought to be generated via proton transfer induced by two histidines highly conserved among the (6-4) photolyases. This intermediate spontaneously rearranges to form an oxetane intermediate by intramolecular nucleophilic attack. In the subsequent light-driven reaction, one electron is believed to be transferred from the fully reduced FAD cofactor (FADH-) to the oxetane intermediate thus forming a neutral FADH radical and an anionic oxetane radical, which spontaneously fractures. The excess electron is then back-transferred to the flavin radical restoring the fully reduced flavin cofactor and a pair of pyrimidine bases [2].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 37290-70-3
1.  Hitomi, K., DiTacchio, L., Arvai, A.S., Yamamoto, J., Kim, S.T., Todo, T., Tainer, J.A., Iwai, S., Panda, S. and Getzoff, E.D. Functional motifs in the (6-4) photolyase crystal structure make a comparative framework for DNA repair photolyases and clock cryptochromes. Proc. Natl. Acad. Sci. USA 106 (2009) 6962–6967. [DOI] [PMID: 19359474]
2.  Schleicher, E., Hitomi, K., Kay, C.W., Getzoff, E.D., Todo, T. and Weber, S. Electron nuclear double resonance differentiates complementary roles for active site histidines in (6-4) photolyase. J. Biol. Chem. 282 (2007) 4738–4747. [DOI] [PMID: 17164245]
[EC created 2009]

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