Lipoxygenase EC

Lipoxygenase (LOX) is a non-haem, iron-containing dioxygenase that catalyses the regioselective and enantioselective dioxygenation of unsaturated fatty acids containing at least one (Z,Z)-l,4-pentadienoic system. For instance, LOX from soy converts linoleic acid to the (S)-13-hydroperoxide [1]. 

It is supposed that the catalytic mechanism proceeds through a free-radical intermediate which reacts directly with oxygen or an organic iron intermediate [63]. The three-dimensional protein structure of the native form of LOX isoenzyme L-1 from soybean has already been described [64, 65]. 

LOX is an important factor in the large-scale use of plant enzymes for the production of natural green note aroma compounds, a group of isomeric C6 aldehydes and alcohols [66]. 

In nature, the green notes are produced after the destruction of the plants tissue (leaves, fruits or vegetables). Destruction of the cell wall leads to a cascade of enzyme-catalysed reactions polyunsaturated fatty acids with the diene system described before are converted into hydroperoxides by LOX catalysis. The hydroperoxide lyase cleaves the hydroperoxides in the whole cascade, oxireduc-tases are involved too. The biotechnological large-scale production of natural green notes follows the natural pathway. 

A patented process for the production of green notes applying bakers yeast for in situ reduction of enzymatically produced aldehydes [67, 68] has been called into question regarding the effective production of (Z)-3-hexenol. According to Gatfield s report [69] the isomerisation of (Z)-3-hexenol to (E)-2-hexenal is a very fast process. The latter undergoes facile conversion to hexanol. Beside this, baker s yeast can add activated acetaldehyde to ( )-2-hexenal, forming 4-octen-2,3-diol. 

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Lipoxygenase (EC 1.13.11.12, nonheme iron dioxygenase), the substrate (polyunsaturated fatty acid) is poorly water soluble and the product (hydroperoxy-fatty acid) is hydrophilic. The reaction occurs in the aqueous phase [85,86]. 

This selenium-dependent enzyme [EC 1.11.1.9] catalyzes the reaction of two molecules of glutathione with hydrogen peroxide to produce glutathione disulfide and two water molecules. Hydrogen peroxide can be replaced by steroid and lipid hydroperoxides, albeit not as effectively (nevertheless, this enzyme is not identical with phospholipid-hydroperoxide glutathione peroxidase [EC 1.11.1.12]). However, the hydroperoxy products formed by the action of lipoxygenase [EC 1.13.11.12] are not substrates. 

Lipoxygenase [EC 1.13.11.12] catalyzes the reaction of linoleate with dioxygen to produce (9Z,11 )-(135 )-13-hydroperoxyoctadeca-9,ll-dienoate. This iron-depen-dent enzyme can also oxidize other methylene-interrupted polyunsaturated fatty acids. See also specific enzyme... 

Lipoxygenase (EC 1.13.11.12) is an enzyme that catalyzes the hydroperoxidation of polyunsaturated fatty acids and esters containing a cis-cis-l, 4-pentadiene system (Table 6). In 1947, Theorell et al. obtained the enzyme in a crystalline form from soybeans and reported that the enzyme neither contained nor required a metal cofactor192. Subsequent studies from three groups of investigators have demonstrated that the enzyme purified from soybeans in an iron-containing dioxygenase74-76 ... 

Lipoxygenases (EC 1.13.11.12, linoleate oxygen oxidoreductase) are found in many plants with soybeans having the highest activity. The characteristics of these enzymes were reviewed recently (Robinson et al., 1995 Gardner, 2003). Fujimaki et al. (1965) showed that lipoxygenase was associated with hexanal production in soybeans. 

The oxidation of catecholamines by the hydroperoxidase activity of lipoxygenase (EC 1.13.11.12) is documented by Rosei et al. (1994) and NOnez-Delicado et al. (1996). o-Diphenols are easily studies spectrophotometrically since, when oxidised, they render coloured compounds, quinones, or their corresponding aminochromes. In the case of isoprenaline the maximum of the oxidation product was developed at 490 nm (NOnez-Delicado et al. 1999), which corresponds to that of the aminochrome product (Jim nez et al. 1985, NOnez-Delicado et al. 1996). 

Lipoxygenase (EC 1.13.11.12) catalyses the stereospecific dioxygenation of polyunsaturated fatty acids containing a l,4-cis,cis-pentadiene system to a pentadienyl radical intermediate which reacts with molecular oxygen to yield ris,trans-conjugated diene hydroperoxides (Wiseman et al. 1988). 

Lipoxygenase (EC 1.13.11.12) catalyzes the dioxygenation of polyunsaturated fatty acids to form their corresponding hydroperoxides. Reduc derivatives of these have the potential to replace ricinoleic acid in industrial products. Currently ricinoleic acid is obtained from castor oil, a commodity that is imported into the U.S. at the level of thirty thousand metric tons per year (1). A method for immobilizing lipoxygenase was developed, and the use of this immobilized preparation to produce die hydroperoxide of linoleic acid (HPOD) in aqueous buffer-organic solvent mixtures was investiga. ... 

This iron-dependent enzyme [EC 1.13.11.34], better known as arachidonate 5-lipoxygenase and occasionally referred to as leukotriene A4 synthase, catalyzes the reaction of arachidonate with dioxygen to produce (6 , 8Z,1 lZ,14Z)-(5S)-5-hydroperoxyicosa-6,8,ll, 14-tetraenoate, which rapidly converts to leukotriene A4. 

Axelrod, B., Cheesebrough, T.M., and Laakso. S. 1981. Lipoxygenase from soybeans. EC... 

The committed biosynthetic path to the leukotrienes begins (see Fig. 5.2) with the action of 5-lipoxygenase (5-LO)[EC 1.13.11.34] (14)on arachidonic acid. Purified human 5-LO is an unstable, 78,000-Da protein that has been isolated and cloned (15,16). It contains a tightly bound, nonheme iron that is essential for enzymatic activity (17). Like all known lipoxygenases, 5-LO catalyzes the insertion of molecular oxygen into a l,4-cis,cis-pentadiene unit. The effect of 5-LO on AA is to abstract stereospecifically the pro-S hydrogen at position C7 and to insert molecular oxygen at... 

It is clear that 5-lipoxygenase (5-LO) [EC 1.13.11.34], through a two-step process, is the enzyme responsible for the production of LTA4. Thus the mechanism of action and, to a lesser extent, the structure of 5-LO have largely influenced the design and discovery of inhibitors of leukotriene biosynthesis. This enzyme has been the subject of intense research since its discovery, as discussed below (Section 5.1), and many inhibitors have been described. 

FIGURE 8.11 First-order reaction rate constants k for heat inactivation, plotted against mass fraction of water w. AP alkaline phosphatase, in skim milk, 80°C. Ec killing of Eschericia coli, in skim milk, 63°C. Ch chymosin, in whey, 80°C. Li lipoxygenase, in sucrose/calcium alginate, 72°C. 

Biosynthesis The endoperoxides PGG2 and PGH2 are formed in the so-called arachidonic acid cascade from eicosatetraenoic acid (arachidonic acid) liberated from membrane phospholipids by phospholipase A2 (EC 3.1.1.4) (see figure under thromboxanes) under the action of cyclooxygenase. All other PG are then formed by further enzymatic reactions. In contrast to other hormones, PG are not stored in the cell but are always newly synthesized when required. The close relatives of the PG, the thromboxanes, prostacyclins, leuko-trienes, and lipoxins are also generated from eicosa-polyenoic acids in the lipoxygenase pathway. For synthesis, see Ut.. ... 

Lipoxygenase (linoleate oxygen oxidoreductase, EC 1.13.11,12) is a term applied to a group of enzymes which catalyse the oxygenation, by molecular oxygen, of fatty acids containing a cw, cw-1, 4-pentadiene system to produce conjugated hydroperoxydiene derivatives (see also Section 10.3) ... 

The presence of a lipid-oxidizing enzyme in plants, then termed lipoxidase, was first described by Andre and Hou in 1932 [1]. A pigment bleaching property, attributed to a separate enzyme activity described as carotene oxidase, was later found to originate from this enzyme as well [2]. The name lipoxygenase (linoleateioxygen oxidoreductase, EC 1.13.11.12) is now used for this enzyme. 

A pendent mercury drop electrode has been used to reduce the 4,5-azomethine group in 1,4-benzodiazepines There were additional contributions from partial reduction of nitro moieties, as in nitrazepam, and A -oxides, as in chlordiazepoxide. The 5-lipoxygenase inhibitor methyl 2-[(3,4-dihydro-3,4-dioxo-l-naphthalenyl) aminojbenzoate (CGS 8515) has been measured in ethyl acetate extracts of plasma from animals treated with the drug using an ODS-modified silica column with methanol-aq. acetate buffer (0.15 mol L, pH 4.5) (60 -f 40) as eluent and EC... 

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