Epoxide Hydrolase EC

A valuable alternative to the above existing methods is the use of cofactor-independent epoxide hydrolases [EC 3.3.2.X]. Enzymes from mammalian sour-... 

This enzyme [EC 3.S.2.6] catalyzes the hydrolysis of (7E,9E,11Z,14Z) - (5vS,6.S) - 5,6 - epoxyicosa - 7,9,11,14 - tetra-enoate to form (6Z,8E,10E,14Z)-(55,12R)-5,12-dihy-droxyicosa-6,8,10,14-tetraenoate. This enzyme is highly specific yet it also converts 4,5-leukotriene A4 into leukotriene B4. Note also that epoxide hydrolase [EC 3.3.2.3] is not identical with this enzyme. 

The term dihydrodiol is widely used in reference to vicinal dihydroxydihydro-derivatives of aromatic hydrocarbons. Although most known and potential benzene oxide or substituted benzene oxide metabolites tend to be quite unstable, a recent study has described the isolation of a relatively stable arene oxide metabolite of 2,2, 5,5 -tetrachlorobiphenyl. Perhaps because of the generally high susceptibility of benzene oxide 1 and many substituted benzene oxides to isomerize to phenols, relatively little has been reported on the kinetics and regiospecificity of their microsomal epoxide hydrolase (EC 3.3.2.3) catalyzed trans hydration to dihydro-... 

Epoxide hydrolase (EC 33.23) activity in pulmonary alveolar macrophages obtained from 11 patients by bronchoalveolar lavage was 0.241 0.10 nmol/ min x mg protein (Petruzzelli et al. 1988). Epoxide hydroxylase activity was 0.161 0.02 nmol/min x mg protein in non-smokers and 0.3110.08 nmol/ min x mg protein in smokers (P <0.001). 

Chiral epoxides and their corresponding vicinal diols are very important intermediates in asymmetric synthesis [163]. Chiral nonracemic epoxides can be obtained through asymmetric epoxidation using either chemical catalysts [164] or enzymes [165-167]. Biocatalytic epoxidations require sophisticated techniques and have thus far found limited application. An alternative approach is the asymmetric hydrolysis of racemic or meso-epoxides using transition-metal catalysts [168] or biocatalysts [169-174]. Epoxide hydrolases (EHs) (EC 3.3.2.3) catalyze the conversion of epoxides to their corresponding vicinal diols. EHs are cofactor-independent enzymes that are almost ubiquitous in nature. They are usually employed as whole cells or crude... 

The cytosolic enzyme leukotriene A4 hydrolase (EC 3.3.2.6), which ster-eoselectively converts leukotriene A4 (LTA4) to leukotriene B4 [56], This enzyme catalyzes the hydrolytic cleavage of the 5,6-epoxide ring in LTA4, but, in contrast to what happens with other EHs, the product is not a vicinal diol but a 5,12-diol. As a zinc metalloenzyme, LTA4 hydrolase does not appear to be related to any other epoxide hydrolase. 

Enzyme catalysed hydrolysis of racemic epoxides is interesting from a practical point of view. This reaction is catalysed by epoxide hydrolases (EHs, EC 3.3.2.3) (Archelas and Furstoss, 1998). Mammalian EHs are the most widely studied and they are divided into five groups among which the soluble (cytosolic) epoxide hydrolases (sEH) and microsomal epoxide hydrolases (mEH) are best charactelised. The mechanism of sEH from rat starts with a nucleophilic attack by Asp333 on a carbon of the epoxide (usually the least hindered one) to form a glycol monoester intermediate which is stabilised by an oxyanion hole. A water molecule activated by His523 releases the 1,2-diol product. An... 

EC 3.3.2 Ether hydrolases EC 3.3.2.9 Microsomal epoxide hydrolase [EPHXI] mEH EC 3.3.2.10 Soluble epoxide hydrolase [EPHX2) sEH... 

Relevant enzymes among the serine hydrolases include car-boxylesterases, arylesterases, cholinesterase and a number of serine endopeptidases [EC 3.4.21], The role of arylsulfa-tases, phosphatases, 3-glucuronidases, epoxide hydrolases and some endopeptidases is also significant. 

The epoxide hydrolases (EHs ECS.3.2.3) hydrate simple epoxides to vicinal diols, and they hydrate arene oxides to trans-dihydrodiols (also see Table 8.1). 

D. Hydration Epoxide hydratase (EC 4.2.1.64), also called epoxide hydrase or hydrolase Epoxides (arene and alkene oxides) Epoxides are hydrated to dihydrodiols. Product glycols which are stereochemically fixed by a ring structure invariably have the /ra/i5-configuration... 

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