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Foods rich with unsaturated fatty acids are prone to enzymatic and nonenzymatic lipid peroxidation; lipoxygenase, a metalloenzyme and a free radical former, oxidizes polyunsaturated fatty acids and is one of the key enzymes in lipid oxidation. Here, we report sclerotiorin, purified from the fermented broth of Penicillium frequentans, as a potent reversible, uncompetitive inhibitor against soybean lipoxygenase-1 (LOX-1) with a half-maximal value (IC50) of 4.2 microM. The inhibitor also showed an antioxidant property by scavenging free radical with an ED50 of 0.12 microM; in addition, nonenzymatic lipid peroxidation was inhibited with a PD50 value of 64 microM and did not show metal chelation. The observations made in this study suggest that sclerotiorin possibly inhibits LOX in two ways: one, by interacting with the enzyme-substrate complex, and two, as an antioxidant by quenching or trapping the free radical intermediates formed in the enzyme reaction. Sclerotiorin compares well with other known natural and synthetic lipoxygenase inhibitors.
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PMID:Sclerotiorin, a novel inhibitor of lipoxygenase from Penicillium frequentans. 1738 79

6-Pentadeca(e)nylsalicylic acids isolated from the cashew Anacardium occidentale L. (Anacardiaceae), commonly known as anacardic acids, inhibited the linoleic acid peroxidation catalyzed by soybean lipoxygenase-1 (EC 1.13.11.12, type 1) competitively without prooxidant effects. Their parent compound, salicylic acid, did not have this inhibitory activity up to 800 pm, indicating that the pentadeca(e)nyl group is an essential element to elicit the activity. The inhibition is attributed to its ability to chelate iron in the enzyme. Thus, anacardic acids chelate iron in the active site of the enzyme and then the hydrophobic tail portion slowly begins to interact with the hydrophobic domain close to the active site. Formation of the anacardic acids-ferric ion complex was detected in the ratio of 2:1 as the base peak in the negative ion electrospray ionization mass spectrometry. Hence, anacardic acids inhibit both Eox and Ered forms.
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PMID:Anacardic acids and ferric ion chelation. 1806 45

Oxylipins constitute a class of molecules notably involved in host-pathogen interactions. In the potato-Phytophthora infestans (Mont.) De Barry (P. infestans) relationships, the role of colneleic and colnelenic acids, two oxylipins resulting from the consecutive action of lipoxygenase (EC 1.13.11.12) and divinyl ether synthase (EC 1.-) on respectively linoleic and linolenic acids have been previously reported. In the present paper, five potato cultivars with contrasting resistance to P. infestans were submitted to infection. Lipoxygenase pathway response was studied at both transcriptional and metabolic levels. A Northern blot preliminary study revealed that lipoxygenase (lox1 and lox3) and divinyl ether synthase genes were clearly up-regulated 96h after leaf inoculation with P. infestans. Profiling of free and esterified oxylipins performed 24h, 48h, 72h and 96h after inoculation, showed that esterified oxylipins are mainly produced with 9-derivatives in higher concentrations (esterified forms of colnelenic acid, 9-hydroxy octadecatrienoic acid, 9-hydroperoxy octadecatrienoic acid). Oxylipin accumulation is undetectable 24h after infection, slightly detectable after 48h, reaching highest concentrations after 96h. Cultivars show slightly different oxylipin profiles but the concentration of individual oxylipins differs markedly 96h after infection. No correlation was found between P. infestans resistance levels and oxylipin synthesis rates or concentration. To assess local and systemic effects of colneleic acid application before P. infestans infection, Bintje cultivar was sprayed with colneleic acid 72h before inoculation. Both application modes (local and systemic) resulted in lipoxygenase pathway activation without affecting the resistance level to the pathogen.
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PMID:Changes in oxylipin synthesis after Phytophthora infestans infection of potato leaves do not correlate with resistance. 1853 77

Soybean lipoxygenase-1 (EC 1.13.11.12) reaction with linoleic acid as substrate was used to study the biocatalysis in a biphasic system when the reactants have surface-active properties. The poorly water-soluble substrate was initially dissolved in an apolar solvent (octane). The hydroperoxide produced was water soluble and remained in the aqueous phase (borate buffer). The bioreactor was a modified Lewis cell with a well-defined interfacial area between the two phases. Two phenomena were studied separately: the reactant transfer between the two phases and the biocatalyzed reaction in an aqueous medium. This allowed determination of the transfer and the reaction constants. Substrate transfer was found to be affected by the progress of the reaction, because linoleic acid and the hydroperoxy acid have an influence on the interfacial tension. Inactivation of the biocatalyst at the interface was observed in the bioreactor. These results indicate that it is impossible to analyze the system behavior with the method proposed in the literature, which is based on the sequential study of the substrate transfer to the aqueous phase and its biocatalysis by lipoxygenase. The interaction between transfer phenomena and reaction kinetics was studied in the biphasic system. The kinetics were different from those obtained in the aqueous medium. Catalysis and transfer influence each other reciprocally. In this compartmentalized system, cooperativity phenomena were obtained using a nonallosteric enzyme. The evolution of the system was modeled (Runge-Kutta algorithm). The curves obtained were very close to those determined experimentally.
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PMID:Investigation of behavior of an enzyme in a biphasic system: soybean lipoxygenase-1. 1862 21

Activity of two enzymes of thiol-disulfide cell metabolism, lipoxygenase (LOX, EC 1.13.11.12) and disulfide-reductase (TPDO, EC 1.8.4.2) was studied in recombinant inbred lines of common wheat ITMI. Their activity in the caryopsis may be connected with the gluten quality, one of the most important traits significant for selection. The activity of lipoxygenase under favorable and droughty environmental conditions was shown to be associated with the quantitative trait locus (QTL) located on chromosome 4BS near the structural gene of a subunit of this enzyme. However, no QTL common to this enzyme and any characteristic of gluten quality have been found. Four loci responsible for the activity of disulfide reductase were identified on chromosomes 4A, 5D, 6A, and7D. Previously, indicators of grain and flour properties, such as elasticity, flour vigor, and grain hardiness were mapped at the same loci. This indicates that the given enzyme participates in the formation of the protein complex upon maturation of wheatgrain. The detected QTL can be involved in further genetic studies designed to establish the regularities of gluten formation.
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PMID:[Mapping of quantitative trait loci (QTL) associated with activity of disulfide reductase and lipoxygenase in grains of durum wheat Triticum aestivum L. seeds]. 1867 99

6-Alkylsalicylic acids inhibit the linoleic acid peroxidation catalyzed by soybean lipoxygenase-1 (EC 1.13.11.12, type 1) competitively and without pro-oxidant effects. This activity is largely dependent on the nature of their alkyl side chains. Inhibitory activities of anacardic acids, viz. 6-pentadec(en)ylsalicylic acids, isolated from the cashew Anacardium occidentale, were initially used for comparison because their aromatic head portions are the same. Consequently, the data should be interpreted to mean that changes in the hydrophobic side chain tail portions of the molecules evaluated correlate with the specific activity determined.
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PMID:Evaluation of lipoxygenase inhibitory activity of anacardic acids. 1881 Sep 98

Lipoxygenases (LOX; linoleate:oxygen oxidoreductase EC 1.13.11.12) consist of a class of enzymes that catalyze the regio- and stereo specific dioxygenation of polyunsaturated fatty acids. Here we characterize two proteins that belong to the less studied class of 9-LOXs, Solanum tuberosum StLOX1 and Arabidopsis thaliana AtLOX1. The proteins were recombinantly expressed in E. coli and the product specificity of the enzymes was tested against different fatty acid substrates. Both enzymes showed high specificity against all tested C18 fatty acids and produced (9S)-hydroperoxides. However, incubation of the C20 fatty acid arachidonic acid with AtLOX1 gave a mixture of racemic hydroperoxides. On the other hand, with StLOX1 we observed the formation of a mixture of products among which the (5S)-hydroperoxy eicosatetraenoic acid (5S-H(P)ETE) was the most abundant. Esterified fatty acids were no substrates. We used site directed mutagenesis to modify a conserved valine residue in the active site of StLOX1 and examine the importance of space within the active site, which has been shown to play a role in determining the positional specificity. The Val576Phe mutant still catalyzed the formation of (9S)-hydroperoxides with C18 fatty acids, while it exhibited altered specificity against arachidonic acid and produced mainly (11S)-H(P)ETE. These data confirm the model that in case of linoleate 9-LOX binding of the substrate takes place with the carboxyl-group first.
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PMID:On the substrate binding of linoleate 9-lipoxygenases. 1903 75

A pot experiment was carried out to investigate the effect of exogenous salicylic acid (SA) on the growth, photosynthesis, oxidative stress and responses of chloroplastic antioxidant defense system of maize (Zea mays L.) plants grown in a nickel (Ni)-contaminated soil. The results indicate that exogenous SA significantly decreased the reduction in dry weight, chlorophyll and beta-carotene contents, and net photosynthetic rate of the Ni-stressed maize, demonstrating an alleviating effect of SA on Ni toxicity of plants. Superoxide anion generation rate, H(2)O(2) and malondialdehyde (MDA) contents, and lipoxygenase (LOX, EC 1.13.11.12) activity significantly increased in the chloroplasts of maize exposed to Ni stress, revealing an oxidative damage occurred in maize chloroplasts, whereas, the values of these parameters were markedly lowered in the SA-treated plants under Ni stress. Application of SA significantly enhanced the activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2), and the poll of reduced ascorbate and glutathione in chloroplasts of the Ni-stressed maize. Accordingly, the fact that SA up-regulates the capacity of antioxidant defense system in chloroplasts, thus reducing the oxidative damage, is involved in the SA-induced alleviation of Ni toxicity in maize.
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PMID:Up-regulation of chloroplastic antioxidant capacity is involved in alleviation of nickel toxicity of Zea mays L. by exogenous salicylic acid. 1937 98

Lipoxygenases (linoleate: oxygen oxidoreductase, EC 1.13.11.12; LOXs) are encoded by a multi-gene family in plants. The LOXs are monomeric non-heme, non-sulfur iron dioxygenases, which catalyze the incorporation of molecular oxygen into polyunsaturated fatty acids containing a cis, cis-1,4-pentadiene moiety. The LOX isoforms are distinguished by differences in optimum pH of the reaction, pI, substrate and product specificity, spatial and temporal expression, and subcellular localization. The function of various LOXs in plants has been suggested. Some of the physiological processes in which lipoxygenases have been implicated include wounding, pathogen attack, seed germination, fruit ripening, plant senescence, and synthesis of Abscisic acid (ABA) and Jasmonic acid (JA). During normal vegetative and reproductive growth, lipoxygenases have also been suggested to act as vegetative storage proteins, participate in transference of lipoid, and response to nutrient stress and source/sink relationships. Significant progress in understanding LOX families will be beneficial to the application of the LOX in crop breeding, research on new-type phytoalexin and food industry.
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PMID:[Advances in plant lipoxygenases research]. 1944 Dec 19

Lipoxygenases (LOXs, EC 1.13.11.12) are a class of non-heme iron containing dioxygenases which catalyze the regiospecific and stereospecific hydroperoxidation of polyunsaturated fatty acids with 1,4-pentadiene system such as linoleic acid and linolenic acid in plants. In this work we studied the LOX activity in damaged as well as in distal leaves in response to specialist (Agraulis vanillae vanillae) or generalist (Spodoptera frugiperda) insect attack. Enzymatic assays showed that induction of LOX activity occurred locally and systemically in response to both insects' attacks. Northern blot analysis revealed that LOX expression is also insect-inducible in agreement with enzymatic assay results. In addition, northern analysis corroborated previous reports that LOX activity is wound- and methyl jasmonate-inducible. These results suggest that the herbivore-response in passion fruit is mediated by jasmonates, since a key enzyme of the biosynthetic pathway of jasmonic acid is induced upon lepidopteran insects' attacks.
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PMID:Herbivore response in passion fruit (Passiflora edulis Sims) plants: induction of lipoxygenase activity in leaf tissue in response to generalist and specialist insect attack. 1999 44


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