Determination of the activity of lipoxygenase (lipoxidase)

Antioxidative and Metabolic Responses in Canola: Strategies with Wood Distillate and Sugarcane Bagasse Ash for Improved Growth under Abiotic Stress

In the context of increasing agricultural challenges posed by soil salinity and drought stress, the main importance of the present study was to evaluate some novel treatments for improving canola productivity and resilience by applying wood distillate (WD) in combination with bagasse ash (SBA). A two-year field experiment using a split plot design was conducted and evaluated several physiological and biochemical parameters under different irrigation regimes conducted at 80% and 50% field capacity. While there were considerable moderation effects of SBA and WD on soil salinity, expressed as exchangeable sodium percentage (ESP), under both well-irrigated and drought conditions, more importantly, the ESP was reduced to 31% under drought stress with combined WD and SBA applications over any single factor. WD and SBA treatments of canola leaves showed reduced Na content with increased K levels, and the plants maintained physiological attributes-chlorophyll content, stomatal conductance, and relative water content-to the level of controls of well-irrigation. Besides, they significantly alleviated oxidative stress by decreasing the hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL) levels and increasing the activities of antioxidant enzymes like superoxide dismutase (SOD) and ascorbate peroxidase (APX). Nonenzymatic antioxidants such as total soluble sugars (TSS), total soluble proteins (TSP), total phenolic content (TPC), and total flavonoid content (TFC) were significantly increased under stress conditions with a special accent on combined treatment, whereas the levels of proline and GB that increased in alignment with drought reduced under the combined application. Various growth parameters of plants like plant height, number of branches, and siliques per plant were significantly improved with WD and SBA under drought stress. Principal component analysis (PCA) and Pearson correlation further confirmed the relationships among these parameters and thus underpinned that WD and SBA can evoke a synergistic effect to enhance growth promotion and stress tolerance in canola. This, therefore, infers that the combined application of WD and SBA can be key, offering very high potential as viable options to better canola productivity under adverse environmental conditions.

Biochar and silicon relegate the adversities of beryllium stress in pepper by modulating methylglyoxal detoxification and antioxidant defense mechanism

Industrial activities have escalated beryllium (Be) release in environment which negatively affect plant growth and human health. This investigation describes Be-induced stress in pepper and its palliation by application of pineapple fruit peel biochar (BC) and potassium silicate (Si). The treatment of Be reduced seedling length, biomass, and physiological attributes and enhanced electrolyte leakage, hydrogen peroxide (H2O2), superoxide (O2•-) level in pepper plants; however, these oxidative stress markers were reduced with combined treatment (Be + BC + Si). Application of BC and Si also lowered Be cumulation in roots and shoots of pepper. Under combined treatment, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities exhibited significant enhancement 19, 7.6, 22.8, and 48%, respectively, in Be-stressed pepper. The Be + BC + Si increased peroxidase (POD), glutathione S-transferase (GPX), and glutathione peroxidase (GST) activities 121, 55, and 53%, respectively, as compared to Be-treated pepper. Methylglyoxal level was reduced in pepper with rise in glyoxalase I and II enzymes. Thus, combined application of SS and BC effectively protects pepper against oxidative stress induced by Be by increasing both antioxidant defense and glyoxalase systems. Hence, pineapple fruit peel biochar along with potassium silicate can be used for enhancing crop productivity under Be-contaminated soil.

Unlocking the potential of co-application of steel slag and biochar in mitigation of arsenic-induced oxidative stress by modulating antioxidant and glyoxalase system in Abelmoschus esculentus L

This study investigates our hypothesis that how effect of arsenic stress on okra (Abelmoschus esculentus L.) can be alleviated through the use of waste materials such as steel slag (SS) and corncob biochar (BC). Different growth variables, biochemical parameters, oxidative stress markers, enzymatic and non-enzymatic antioxidants and glyoxylase enzyme activities were assessed. When okra was exposed to As, there was a noticeable decrease in seedling length, biomass, relative water content, various biochemical attributes, however, electrolyte leakage and lipid peroxidation in okra were enhanced. The supplementation of SS and BC-either individually or in combination-improved the growth parameters and reduced oxidative stress markers. Application of SS and BC also lowered As accumulation in roots and shoots of okra mitigating adverse effects of As exposure. Additionally, the activities of antioxidant and glyoxalase enzyme increased when SS and BC were present, concurrently reducing methylglyoxal content. Arsenic-induced stress led to oxidative damage, an enhancement in both enzymatic and non-enzymatic antioxidants, induced the synthesis of thiol and phytochelatins in roots and shoots. These may play a vital function in alleviating oxidative stress induced by As. Superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase activities were significantly enhanced in As-treated plants. These enhancement were further amplified when SS and BC were amended to As-treated okra. Therefore, synergistic application of SS and BC effectively protects okra against oxidative stress induced by As by increasing both antioxidant defense and glyoxalase systems. Both SS, an industrial byproduct, and BC, generated from agricultural waste, are cost-effective, environmentally friendly, safe, and non-toxic materials which can be used for crop production in As contaminated soil.

A review of thermosensitive antinutritional factors in plant-based foods

Legumes and cereals account for the vast proportion of people's daily intake of plant-based foods. Meanwhile, a large number of antinutritional factors in legumes and cereals hinder the body absorption of nutrients and reduce the nutritional value of food. In this paper, the antinutritional effects, determination, and passivation methods of thermosensitive antinutritional factors such as trypsin inhibitors, urease, lipoxygenase, and lectin were reviewed to provide theoretical help to reduce antinutritional factors in food and improve the utilization rate of plant-based food nutrition. Since trypsin inhibitors and lectin have been more extensively studied and reviewed previously, the review mainly focused on urease and lipoxygenase. This review summarized the information of thermosensitive antinutritional factors, trypsin inhibitors, urease, lipoxygenase, and lectin, in cereals and legumes. The antinutritional effects, and physical and chemical properties of trypsin inhibitors, urease, lipoxygenase, and lectin were introduced. At the same time, the research methods for the detection and inactivation of these four antinutritional factors were also summarized in the order of research conducted time. The rapid determination and inactivation of antinutrients will be the focus of attention for the food industry in the future to improve the nutritional value of food. Exploring what structural changes could passivation technologies bring to antinutritional factors will provide a theoretical basis for further understanding the mechanisms of antinutritional factor inactivation. PRACTICAL APPLICATIONS: Antinutritional factors in plant-based foods hinder the absorption of nutrients and reduce the nutritional value of the food. Among them, thermosensitive antinutritional factors, such as trypsin inhibitors, urease, lipoxygenase, and lectins, have a high proportion among the antinutritional factors. In this paper, we investigate thermosensitive antinutritional factors from three perspectives: the antinutritional effect of thermosensitive antinutritional factors, determination, and passivation methods. The current passivation methods for thermosensitive antinutritional factors revolve around biological, physical, and chemical aspects, and their elimination mechanisms still need further research, especially at the protein structure level. Reducing the level of antinutritional factors in the future food industry while controlling the loss of other nutrients in food is a goal that needs to be balanced. This paper reviews the antinutritional effects of thermosensitive antinutritional factors and passivation methods, expecting to provide new research ideas to improve the nutrient utilization of food.

Zinc Oxide Nanoparticles Improve Pleioblastus pygmaeus Plant Tolerance to Arsenic and Mercury by Stimulating Antioxidant Defense and Reducing the Metal Accumulation and Translocation

The utilization of nanoparticles to potentially reduce toxicity from metals/metalloids in plants has increased in recent years, which can help them to achieve tolerance under the stressful conditions. An in vitro experiment was conducted to investigate five different levels of zinc oxide nanoparticles (ZnO-NPs; 0, 50, 100, 150, and 200 μM) both alone and in combination with 150 μM arsenic (As) and 150 μM mercury (Hg) in one-year-old Pleioblastus pygmaeus (Miq.) Nakai plants through four replications. The results demonstrated that As and Hg alone had damaging effects on the plant growth and development. However, the addition of various concentrations of ZnO-NPs led to increased antioxidant activity, proline (79%) content, glycine betaine (71%) content, tyrosine ammonia-lyase (43%) activity, phenylalanine ammonia-lyase (69%) activity, chlorophyll indices, and eventually plant biomass, while the lipoxygenase activity, electrolyte leakage, soluble protein, hydrogen peroxide content, and thiobarbituric acid reactive substances were reduced. We concluded that ZnO-NPs detoxified As and Hg toxicity in the plants through increasing antioxidant activity, reducing As and Hg accumulation, As and Hg translocation from roots to shoots, and adjusting stomatal closure. This detoxification was further confirmed by the reduction of the translocation factor of As and Hg and the enhancement of the tolerance index in combination with ZnO-NPs. However, there is a need for further investigation with different metals/metalloids.

Tumor-killing nanoreactors fueled by tumor debris can enhance radiofrequency ablation therapy and boost antitumor immune responses

Radiofrequency ablation (RFA) is clinically adopted to destruct solid tumors, but is often incapable of completely ablating large tumors and those with multiple metastatic sites. Here we develop a CaCO₃-assisted double emulsion method to encapsulate lipoxidase and hemin with poly(lactic-co-glycolic acid) (PLGA) to enhance RFA. We show the HLCaP nanoreactors (NRs) with pH-dependent catalytic capacity can continuously produce cytotoxic lipid radicals via the lipid peroxidation chain reaction using cancer cell debris as the fuel. Upon being fixed inside the residual tumors post RFA, HLCaP NRs exhibit a suppression effect on residual tumors in mice and rabbits by triggering ferroptosis. Moreover, treatment with HLCaP NRs post RFA can prime antitumor immunity to effectively suppress the growth of both residual and metastatic tumors, also in combination with immune checkpoint blockade. This work highlights that tumor-debris-fueled nanoreactors can benefit RFA by inhibiting tumor recurrence and preventing tumor metastasis.

Consequences of copper treatment on pigeon pea photosynthesis, osmolytes and antioxidants defense

An attempt was made to explore the effect of copper sulphate treatment on growth, photosynthesis, osmolytes and antioxidants in 15 days old seedlings of C. cajan (Pigeonpea). C. cajan seedlings were grown in 0, 1, 5 and 10 mM concentrations of copper sulphate in petriplates lined with Whatman filter paper for 15 days. Root length and shoot length was decreased in a dose dependent manner with highest decrease of 82.80 and 45.92% in 10 mM Cu stress. Photosynthetic efficiency (qP, qN and Y) was decreased in a dose dependent manner whereas NPQ was increased in 1 and 5 mM and decreased in 10 mM Cu. Photosynthetic pigments viz total chlorophyll and carotenoids were increased in low concentrations and decreased in high concentrations of Cu. Osmolytes such as proline, glycine betaine and sugars were found to be increased in a dose dependent manner. Similarly antioxidants such as superoxide dismutase and catalase increased to 129.17 and 169.7%, respectively under Cu stress. Vitamin C and vitamin E was also increased in different concentrations of Cu to a significant level. It can be concluded from the present study that C. cajan can tolerate Cu stress up to 5 mM by adjusting the proportion of proline, glycine betaine, sugars and vitamins along with increasing the activity of some of the antioxidant enzymes.

Cooking influence on physico-chemical fruit characteristics of eggplant (Solanum melongena L.)

Physico-chemical traits of three eggplant genotypes ("Tunisina", "Buia" and "L 305") were evaluated before and after two cooking treatments (grilling and boiling). Different genotypes revealed different changes after cooking, with "Tunisina" showing a better retention of phytochemicals with respect to other two genotypes. The main physical phenomena were water loss during grilling, and dry matter loss after boiling. Chlorogenic acid, the main phenolic in eggplant, resulted higher in grilled samples, while delphinidin glycosides resulted more retained in boiled samples. Glycoalkaloids, thiols and biogenic amines were generally stable, while 5-hydroxy-methyl-furfural was found only in grilled samples. Interestingly, Folin-Ciocalteu index and free radical scavenging capacity, measured with three different assays, were generally increased after cooking, with a greater formation of antioxidant substances in grilled samples. NMR relaxation experiments clarified the hypothesis about the changes of eggplant compounds in terms of decomposition of larger molecules and production of small ones after cooking.

Near-isogenic lines of Triticum aestivum with distinct modes of resistance exhibit dissimilar transcriptional regulation during Diuraphis noxia feeding

Russian wheat aphid (Diuraphis noxia, Kurdjumov) feeding on susceptible Triticum aestivum L. leads to leaf rolling, chlorosis and plant death - symptoms not present in resistant lines. Although the effects of several D. noxia (Dn) resistance genes are known, none have been isolated or characterized. Wheat varieties expressing different Dn genes exhibit distinct modes of D. noxia resistance, such as antibiosis (Dn1), tolerance (Dn2), and antixenosis (Dn5). However, the mechanism whereby feeding aphids are perceived, and how subsequent transcriptional responses are partitioned into resistance categories, remains unclear. Here we report on downstream events in near-isogenic wheat lines containing different Dn genes after D. noxia biotype SA1 feeding. Transcripts involved in stress, signal transduction, photosynthesis, metabolism and gene regulation were differentially regulated during D. noxia feeding. Expression analyses using RT-qPCR and RNA hybridization, as well as enzyme activity profiling, provide evidence that the timing and intensity of pathways induced are critical in the development of particular modes of resistance. Pathways involved include the generation of kinase signalling cascades that lead to a sustained oxidative burst, and a hypersensitive response that is active during antibiosis. Tolerance is a passive resistance mechanism that acts through repair or de novo synthesis of photosystem proteins. Results further suggest that ethylene-mediated pathways are possibly involved in generating volatile compounds and cell wall fortification during the antixenosic response.

Hypervirulent Diuraphis noxia (Hemiptera: Aphididae) biotype SAM avoids triggering defenses in its host (Triticum aestivum) (Poales: Poaceae) during feeding

In the molecular arms race between aphids and plants, both organisms rely on adaptive strategies to outcompete their evolutionary rival. In the current study, we investigated the difference in elicited defense responses of wheat (Triticum aestivum L.) near-isogenic lines with different Dn resistance genes, upon feeding by an avirulent and hypervirulent Diuraphis noxia Kurdjumov biotype. After measuring the activity of a suite of enzymes associated with plant defense, it became apparent that the host does not recognize the invasion by the hypervirulent aphid because none of these were induced, while feeding by the avirulent biotype did result in induction of enzyme activity. Genomic plasticity in D. noxia may be a likely explanation for the observed differences in virulence between D. noxia biotype SA1 and SAM, as demonstrated in the current study.

Mitochondria induce oxidative stress, generation of reactive oxygen species and redox state unbalance of the eye lens leading to human cataract formation: disruption of redox lens organization by phospholipid hydroperoxides as a common basis for cataract disease

The aging eye appears to be at considerable risk from oxidative stress. Lipid peroxidation (LPO) is one of the mechanisms of cataractogenesis, initiated by enhanced promotion of oxygen free radicals in the eye fluids and tissues and impaired enzymatic and non-enzymatic antioxidant defenses of the crystalline lens. The present study proposes that mitochondria are one of the major sources of reactive oxygen species (ROS) in mammalian and human lens epithelial cells and that therapies that protect mitochondria in lens epithelial cells from damage and reduce damaging ROS generation may potentially ameliorate the effects of free radical-induced oxidation that occur in aging ocular tissues and in human cataract diseases. It has been found that rather than complete removal of oxidants by the high levels of protective enzyme activities such as superoxide dismutase (SOD), catalase, lipid peroxidases in transparent lenses, the lens conversely, possess a balance between peroxidants and antioxidants in a way that normal lens tends to generate oxidants diffusing from lenticular tissues, shifting the redox status of the lens to become more oxidizing during both morphogenesis and aging. Release of the oxidants (O(2)(-)·, H(2)O(2) , OH·, and lipid hydroperoxides) by the intact lenses in the absence of respiratory inhibitors indicates that these metabolites are normal physiological products inversely related to the lens life-span potential (maturity of cataract) generated through the metal-ion catalyzed redox-coupled pro-oxidant activation of the lens reductants (ascorbic acid, glutathione). The membrane-bound phospholipid (PL) hydroperoxides escape detoxification by the lens enzymatic reduction. The lens cells containing these species would be vulnerable to peroxidative attack which trigger the PL hydroperoxide-dependent chain propagation of LPO and other damages in membrane (lipid and protein alterations). The increased concentrations of primary LPO products (diene conjugates, lipid hydroperoxides) and end fluorescent LPO products were detected in the lipid moiety of the aqueous humor samples obtained from patients with cataract as compared to normal donors. Since LPO is clinically important in many of the pathological effects and aging, new therapeutic modalities, such as patented N-acetylcarnosine prodrug lubricant eye drops, should treat the incessant infliction of damage to the lens cells and biomolecules by reactive lipid peroxides and oxygen species and "refashion" the affected lens membranes in the lack of important metabolic detoxification of PL peroxides. Combined in ophthalmic formulations with N-acetylcarnosine, mitochondria-targeted antioxidants are promising to become investigated as a potential tool for treating a number of ROS-related ocular diseases, including human cataracts.

Antioxidant activity in vitro of the selenium-contained protein from the Se-enriched Bifidobacterium animalis 01

Several studies indicated that bifidobacteria possessed strong antioxidant activity. In present study, the antioxidant activities of Bifidobacterium animalis 01 proteins were evaluated using six assays, namely, linoleic acid preoxidation assay, erythrocyte hemolysis assay, 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, reducing power assay, hydroxyl (.OH) and superoxide radicals (.O(2)(-)) assays, in which the last two assays were measured by electron spin resonance (ESR). There were two kinds of B. animalis 01 proteins in this study, the regular B. animalis 01 protein (Pro-CK) and the B. animalis 01 selenium-contained protein (Pro-Se). Both Pro-CK and Pro-Se showed concentration dependent antioxidant activity in DPPH assay, reducing power assay and erythrocyte hemolysis assay. All results of six assays indicated that the antioxidant activity of the B. animalis 01 protein was improved remarkably after selenium was incorporated. The antioxidant activity of Pro-Se increased with the increase of selenium content in Pro-Se suggesting selenium played a positive role in enhancing the antioxidant activity of B. animalis 01 protein. Moreover, organic selenium was more effective than inorganic selenium on enhancing the hydroxyl radical scavenging ability of B. animalis 01 protein.

Molecular and functional characterization of a rose lipoxygenase cDNA related to flower senescence

A cDNA encoding lipoxygenase, Rlox1, was isolated from a cDNA library of senescing rose petals using tomato lipoxygenase cDNA fragments as probes. Characterization of the Rlox1 protein expressed in Echerichia coli revealed that the Rlox1 protein was a soluble lipoxygenase with an unusual optimal pH in the acidic region (pH 4.5-5.0). Northern blot analysis showed that the transcript of the Rlox1 gene was dramatically increased in response to senescence of rose petals. Treatment of rose flowers with ethylene also elevated the mRNA of the Rlox1 gene. These results suggest that the Rlox1 lipoxygenase is involved in senescence of rose flowers.

Antioxidant and eicosanoid enzyme inhibition properties of pomegranate seed oil and fermented juice flavonoids

The antioxidant and eicosanoid enzyme inhibition properties of pomegranate (Punica granatum) fermented juice and seed oil flavonoids were studied. The pomegranate fermented juice (pfj) and cold pressed seed oil (pcpso) showed strong antioxidant activity close to that of butylated hydroxyanisole (BHA) and green tea (Thea sinensis), and significantly greater than that of red wine (Vitis vitifera). Flavonoids extracted from pcpso showed 31-44% inhibition of sheep cyclooxygenase and 69-81% inhibition of soybean lipoxygenase. Flavonoids extracted from pfj showed 21-30% inhibition of soybean lipoxygenase though no significant inhibition of sheep cyclooxygenase. The pcpso was analyzed for its polyphenol content and fatty acid composition. Total polyphenols in pcpso showed a concentration by weight of approximately 0.015%. Pcpso fatty acid composition showed punicic acid (65.3%) along with palmitic acid (4.8%), stearic acid (2.3%), oleic acid (6.3%), linoleic acid (6.6%) and three unidentified peaks from which two (14.2%) are probably isomers of punicic acid (El-Shaarawy, M.I., Nahpetian, A., 1983). Studies on pomegranate seed oil. Fette Seifen Anstrichmittel 83(3), 123-126).

Lipophilic flavonoids from Orthosiphon spicatus prevent oxidative inactivation of 15-lipoxygenase

15-Lipoxygenase from soybeans is inactivated by bubbling air through enzyme solutions. This inactivation is prevented by flavonoids from the East Asian medicinal plant Orthosiphon spicatus, previously found to be inhibitors of the enzyme. 5,7,4'-Trimethylapigenin, eupatorin and 5,7,3',4'-tetramethylluteolin show the strongest enzyme-stabilizing effects, decreasing loss of activity by 50% at concentrations of 2.0 +/- 0.04, 2.4 +/- 0.3 and 4.3 +/- 1.1 microM, respectively. There is no significant correlation between enzyme-inhibiting and enzyme-stabilizing effect. The Orthosiphon flavonoids show radical-scavenging activity towards the diphenylpicrylhydrazyl radical. This is correlated to their enzyme-stabilizing effect, but not to their inhibitory activity towards 15-lipoxygenase. When the enzyme is inactivated by air bubbling, a loss of sulfhydryl groups is observed. Sinensetin, a poor stabilizer of the enzyme, shows less efficiency in protecting sulfhydryl groups than tetramethylscutellarein, which stabilizes the enzyme more efficiently. Thus, oxidation of sulfhydryl groups may contribute to the observed air-induced inactivation of 15-lipoxygenase.

Stimulation of leukotriene production and membrane translocation of 5-lipoxygenase by cross-linking of the IgE receptors in RBL-2H3 cells

Recent studies in rat basophilic leukemia cells (RBL-2H3) have shown that two pharmacological agents, ionomycin and thapsigargin, induce leukotriene C4 production and translocation of 5-lipoxygenase from cytosol to membrane, primarily by causing an influx of extracellular calcium. In the present study, we investigate the induction of these events by receptor activation. Cross-linking of high-affinity IgE receptors (Fc epsilon RI) by antigen in RBL-2H3 cells leads to leukotriene C4 production and membrane translocation of 5-lipoxygenase. As in the ionomycin-stimulated cells, leukotriene C4 production in antigen-stimulated cells is calcium-dependent since the amount of leukotriene C4 produced correlates quantitatively with the increase in intracellular free calcium concentration ([Ca2+]i). However, the increase in [Ca2+]i required for equivalent leukotriene C4 production by antigen is not as high as it is using ionomycin. In addition, no threshold [Ca2+]i level is required for leukotriene production by antigen, which is in contrast to the ionomycin stimulation that a [Ca2+]i level of 300-400 nM is required. Furthermore, antigen causes an additive increase in leukotriene C4 production in cells stimulated by the ionomycin. These results suggest that another as yet unidentified intracellular pathway acts in conjunction with Ca2+ for leukotriene synthesis in antigen-stimulated cells. Antigen stimulation causes 20-30% of the total cell 5-lipoxygenase to associate with membranes (compared with 10% in unstimulated cells) as demonstrated by enzyme activity assay and by Western Blot using antibodies to 5-lipoxygenase.(ABSTRACT TRUNCATED AT 250 WORDS)

Product yield in oxygenation of linoleate by soybean lipoxygenase: the value of the molar extinction coefficient in the spectrophotometric assay

Two iodimetric methods and a gravimetric method were used to determine the spectrophotometric molar absorptivity of the purified product of lipoxygenase-catalyzed dioxygenation of linoleate (13-LS-hydroperoxy-cis,trans-9,11-octadecadienoate). Earlier determinations had led to the use of values varying from 24,000 to 28,000 M-1 cm-1 for epsilon at 235 nm. In the current work, the two iodimetric values (spectrophotometric and titrimetric) average 22,500, while gravimetric analysis of scrupulously purified material gives 22,900. Final 235-nm absorbancies for lipoxygenase runs over a wide range of linoleic acid concentrations up to 200 microM give a constant final percentage completion. If one assumes a 100% reaction, epsilon is 23,600. Each method has less than 1.5% standard error; the average of the three independent methods is 23,000 +/- 580 (2.5%), all being lower than the previous values. In the enzyme-catalyzed reaction of linoleate at less than 200 microM substrate, only 235-nm-absorbing material is formed. Above 200 microM linoleate, yields at 235 nm decrease and yields of materials absorbing at 280 nm increase (the latter is known to arise from lipoxygenase-catalyzed reaction of linoleyl hydroperoxide). Below 200 microM substrate, linoleate purified by HPLC produces only one HPLC-observable product, 13-linoleyl hydroperoxide. At higher substrate concentrations other HPLC peaks arise, again with higher wave-length absorptions. Spectrophotometric data using the epsilon determined here agree with those from the O2 electrode. It is concluded that at S less than 200 microM, saturating air, and sufficient enzyme, soybean lipoxygenase-1 produces a sole product and the reaction proceeds to completion.

Oxidative interactions between fatty acid peroxy radicals and quinones: possible involvement in cyanide-resistant electron transport in plant mitochondria

The interactions between duroquinol, linoleic acid, and lipoxygenase have been followed spectrophotometrically in the uv (210-340 nm) in a simple reaction medium (5 mM [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid] buffer, pH 6.0). Duroquinol is oxidized by reacting with the peroxy radicals of linoleic acid generated in the presence of lipoxygenase. This oxidation is insensitive to cyanide but is sensitive to salicylhydroxamic acid, propylgallate, and disulfiram, the known inhibitors of lipoxygenase and of the cyanide-resistant electron transport pathway of plant mitochondria. This reaction is proposed as a model for the functioning of this pathway in plant mitochondria.