Calcium modulates membrane association, positional specificity, and product distribution in dual positional specific maize lipoxygenase-1

This study investigates how calcium modulates the properties of dual positional specific maize lipoxygenase-1, including its interaction with substrate, association with subcellular membrane and alteration of product distribution. Bioinformatic analyses identified Asp(38), Glu(127) and Glu(201) as putative calcium binding residues and Leu(37) as a flanking hydrophobic residue also potentially involved in calcium-mediated binding of the enzyme to subcellular membranes. Asp(38) and Leu(37) were shown to be important but not essential for calcium-mediated association of maize lipoxygenase-1 to subcellular membranes in vitro. Kinetic studies demonstrate that catalytic efficiency (Vmax/Km) shows a bell-shaped dependence on log of the molar ratio of substrate to unbound calcium. Calcium also modulates product distribution of the maize lipoxygenase-1 reaction, favoring 13-positional specificity and increasing the relative amount of (E,Z)-isomeric products. The results suggest that calcium regulates the maize lipoxygenase-1 reaction by binding to substrate, and by promoting binding of substrate to enzyme and association of maize lipoxygenase-1 to subcellular membranes.

Maternal dietary omega-3 fatty acid intake increases resolvin and protectin levels in the rat placenta

Placental inflammation is associated with several pregnancy disorders. Inflammation is limited by anti-inflammatory and proresolving mechanisms, the latter partly mediated by resolvins and protectins derived from omega-3 polyunsaturated fatty acids (n-3PUFA). We examined effects of dietary n-3PUFAs on levels of resolvins, protectins, and lipoxygenase (ALOX) enzymes in the rat placenta. Rats consumed standard (Std) or high n-3PUFA (Hn3) diets from day 1 of pregnancy; tissues were collected on day 17 or 22 (term = day 23). Maternal Hn3 diet increased resolvin and protectin precursors, 18R/S-HEPE (P < 0.001), and 17R/S-HDHA (P < 0.01) at both days. Resolvins (17R-RvD1 and RvD1) increased at day 22 (P < 0.001) after Hn3 consumption, coincident with higher Alox15b and Alox5 mRNA expression, while RvD2 increased at both days (P < 0.05). Protectins, PD1, and 10S,17S-DiHDHA increased over late gestation (P < 0.001), coincident with higher Alox15 mRNA expression (P < 0.001) and further increased with Hn3 diet (P < 0.05). Maternal systemic and placental proinflammatory mediators were not suppressed by Hn3 diet; systemic IL1β, placental Il1β, and Il6 mRNA expression increased marginally with Hn3 at day 22 (P < 0.001), while Ptgs1 (Cox1) expression increased both days (P < 0.05). Our data indicate that maternal n-3PUFA supplementation enhances expression of enzymes in the n-3PUFA metabolic pathway and increases placental levels of resolvins and protectins.

High-throughput assay for detection of soybean lipoxygenase-1

A high-throughput assay was developed to detect soybean lipoxygenase 1 (LOX-1) using a multilabel plate reader. The assay was also adapted to a single cell fluorometer. Fluorescein is degraded by linoleic hydroperoxide produced from soybean lipoxygenase and linoleic acid. The decrease in fluorescence is measured over time, and the area-under-the-curve (AUC) is used to quantify the LOX-1 content of soybean extract. A dose-dependent response is seen with varied dilutions of pure LOX enzyme or soybean extracts. Percent recovery was between 97% and 108%, and relative standard deviation was 4.3%. Advantages of the assay include the reduced preparation time of samples and reduced use of reagents in the high-throughput assay. Multiple samples can be measured in a single run with a multilabel plate reader.

Antioxidant and anti-inflammatory activities of bean ( Phaseolus vulgaris L.) hulls

Hulls obtained by mechanical abrasive dehulling from four bean cultivars were extracted with two solvents, aqueous (70%) acetone and water, and the extracts evaluated for antioxidant and anti-inflammatory activities in relation to their phenolic contents. Total phenolic content and antioxidant activity of bean hulls, measured using oxygen radical absorbance capacity (ORAC) values, were 6-8-fold those of corresponding whole beans. Aqueous acetone (70%) extracted over twice the amount of total phenolics from hulls that exhibited significantly higher antioxidant and stronger inhibitory effect on both cyclooxygenases, COX-1 and COX-2, than water. Acetone extract of black bean hull exhibited strong COX-1 (IC(50) = 1.2 microg/mL) and COX-2 (IC(50) = 38 microg/mL) inhibitory effects, even outperforming aspirin. Bean hull water extracts were stronger inhibitors of lipoxygenase, 15-LOX, than corresponding acetone extracts. Anti-inflammatory activity of bean hulls was dependent on their phenolic content and antioxidant activity that were significantly affected by cultivar and extracting solvent.

Lipoxygenase distribution in coffee (Coffea arabica L.) berries

In this paper lipoxygenase (LOX) presence was investigated in coffee berries to determine its involvement in lipid degradative metabolism of plants grown in organic and conventional cultivations. An immunochemical analysis has evidenced a ca. 80 kDa protein, cross-reacting with an anti-LOX antibody, only in the pulp fraction of berries obtained from plants of both cultivations. LOX activity in this fraction could be monitored either as conjugated diene formation or reaction products (determined by HPLC) and was mainly associated with a heavy membrane fraction (HMF, enriched in tonoplast, endoplasmic reticulum, plasma membrane, and mitochondria) and a light membrane fraction (LMF, enriched in plasma membrane and endoplasmic reticulum, with low levels of tonoplast and mitochondria). The LOX activity of LMF from berries of both cultivations showed an optimum at pH 8.0. The HMF exhibited a different activity peak in samples from conventional (pH 8.0) and organic (pH 5.5) cultures, suggesting the presence of different isoenzymes. These findings were also confirmed by variation of the ratio of 9- and 13-hydroperoxides in organic (1:1) and conventional cultivations (1:10), indicating that the organic one was subjected to an oxidative stress in the coffee pulp fraction leading to the expression of an acidic LOX. Such de novo synthesized LOX activity could be responsible for the production of secondary metabolites, which may interfere with the organoleptic profile of coffee.

Differential distribution of the lipoxygenase pathway enzymes within potato chloroplasts

The lipoxygenase pathway is responsible for the production of oxylipins, which are important compounds for plant defence responses. Jasmonic acid, the final product of the allene oxide synthase/allene oxide cyclase branch of the pathway, regulates wound-induced gene expression. In contrast, C6 aliphatic aldehydes produced via an alternative branch catalysed by hydroperoxide lyase, are themselves toxic to pests and pathogens. Current evidence on the subcellular localization of the lipoxygenase pathway is conflicting, and the regulation of metabolic channelling between the two branches of the pathway is largely unknown. It is shown here that while a 13-lipoxygenase (LOX H3), allene oxide synthase and allene oxide cyclase proteins accumulate upon wounding in potato, a second 13-lipoxygenase (LOX H1) and hydroperoxide lyase are present at constant levels in both non-wounded and wounded tissues. Wound-induced accumulation of the jasmonic acid biosynthetic enzymes may thus commit the lipoxygenase pathway to jasmonic acid production in damaged plants. It is shown that all enzymes of the lipoxygenase pathway differentially localize within chloroplasts, and are largely found associated to thylakoid membranes. This differential localization is consistently observed using confocal microscopy of GFP-tagged proteins, chloroplast fractionation, and western blotting, and immunodetection by electron microscopy. While LOX H1 and LOX H3 are localized both in stroma and thylakoids, both allene oxide synthase and hydroperoxide lyase protein localize almost exclusively to thylakoids and are strongly bound to membranes. Allene oxide cyclase is weakly associated with the thylakoid membrane and is also detected in the stroma. Moreover, allene oxide synthase and hydroperoxide lyase are differentially distributed in thylakoids, with hydroperoxide lyase localized almost exclusively to the stromal part, thus closely resembling the localization pattern of LOX H1. It is suggested that, in addition to their differential expression pattern, this segregation underlies the regulation of metabolic fluxes through the alternative branches of the lipoxygenase pathway.

Different protection mechanisms after pretreatment with glycine or alpha-lipoic acid in a rat model of warm hepatic ischemia

BACKGROUND/AIM

Alpha-lipoic (LA) acid pretreatment has previously been described to reduce ischemia/reperfusion injury (IRI) after warm liver ischemia, whereas glycine pretreatment has been shown to be protective mostly in models of cold hepatic ischemia. The aim of this study was to determine whether glycine decreases IRI after warm hepatic ischemia. Furthermore we investigated whether doses of LA other than those used previously are also protective against IRI after warm hepatic ischemia.

METHODS

Selective liver ischemia was maintained over a period of 90 min. In long-term as well as short-term experiments we studied IRI in several groups comparing animal survival as the pivotal endpoint.

RESULTS

Animal survival was improved by glycine and 5,000 micromol LA, whereas all animals died within 3 days after pretreatment with 50 micromol LA. In the glycine group we observed a tendency towards decreased apoptosis-related cell death measured by the activity of caspase-3 in liver tissue and the percentage of TUNEL-positive hepatocytes in comparison to the untreated group. Serum alpha-glutathione S-transferase, lipid peroxidation, and caspase-3 activity as well as the percentage of TUNEL-positive hepatocytes and the percentage of liver necrosis were only significantly decreased by 5,000 micromol LA pretreatment. Liver tissue levels of tumor necrosis factor (TNF)alpha were reduced only in the glycine group whereas TNFalpha was increased in the untreated as well as the LA group. Levels of TNFalpha mRNA were upregulated in both the glycine- and LA-pretreated groups.

CONCLUSION

Our data show that increased animal survival by glycine was accompanied by a reduced TNFalpha content in liver tissue. Protection by glycine is likely to result from a reduction in adverse TNFalpha effects. Administration of high-dose LA on the other hand led to a significant reduction in necrosis- and apoptosis-related cell death in IRI of the liver without a reduction in liver TNFalpha.

Lipoxygenase involvement in ripening strawberry

The enzymatic activity, subcellular localization, and immunolocalization of plant lipoxygenase (LOX) in strawberry fruits (Fragaria x ananassa, Duch) were investigated. Chemical and enzymatic properties of LOX have been characterized, and the LOX capability of oxygenating free and esterified unsaturated fatty acids into C6 volatile aldehydes has been confirmed. Fruits at unripe, turning, and ripe stages were analyzed for LOX activity and protein localization by Western blots, two-dimensional electrophoresis, and immunolocalization analyses. The ability of strawberry tissues to in vivo metabolize linolenic acid or linoleic acid into C6 volatile aldehydes and the LOX products was also analyzed. Analysis of strawberry proteins showed that a number of LOX forms, corresponding to at least two mobility groups of approximately 100 and 98 kDa and pI values ranging between 4.4 and 6.5, were present. Confocal and electron microscopy analyses support the idea that LOX proteins are associated to lipid-protein aggregates. Both exogenously supplied linoleate and linolenate were converted into hexanal and trans-2-hexenal at the three fruit-ripening stages. Our experiments suggest the presence of different LOX isoforms in strawberry fruits and that the lipoxygenase-hydroperoxide lyase pathway plays a role in converting lipids to C6 volatiles during ripening.

Fourier transform infrared study of lipoxygenase conformation in organic solvent media

The secondary structure of commercially purified soybean lipoxygenase (EC 1.13.11.12) was investigated in selected monophasic organic solvents, including chloroform, methanol, acetonitrile, hexane, and octane. The Fourier transform infrared (FT-IR) spectra of the enzyme obtained in chloroform, methanol, and acetonitrile showed an absorption band at 1617 cm(-1) indicative of significant protein aggregation, whereas spectra of lipoxygenase in hexane and octane exhibited substantially less aggregate formation. Variable-temperature infrared studies of lipoxygenase in D(2)O show that the predominately alpha-helical structure of the protein undergoes an irreversible transition to intermolecular beta-sheet at and above 65 degrees C. Chemical imaging technology employing an FT-IR spectrometer equipped with an infrared microscope and a focal-plane array detector was used to examine the changes in the secondary structure of lipoxygenase at the water-hexane interface in the presence and absence of substrate. The secondary structure of lipoxygenase at the hexane-water interface was comparable to that of the structure of lipoxygenase in D(2)O after exposure of lipoxygenase solution to hexane.

Regulated spatial distribution of cyclooxygenases and lipoxygenases in Crohn's ulcer

BACKGROUND AND AIMS

Arachidonic acid metabolism actively participates in the initiation, climaxing, and resolution phases of inflammation, and its close connection with inflammatory bowel diseases has been only recently discovered. We aimed to clarify the role of different arachidonic pathways and the interrelationships between them in Crohn's disease.

METHODS

Seventeen specimens of Crohn's disease dated between 2003/1/1 and 2005/1/1 were collected and underwent immunohistochemical analyses with cylcooxygenase 1, cyclooxygenase 2, 5-lipoxygenase, and 15-lipoxygenase-1 antibodies.

RESULTS

(1) The spatial distribution of the three leading enzymes in arachidonic acid pathway--cyclooxygenase 2, 5-lipoxygenase, and 15-lipoxygenase-1--followed sequential arrangement in Crohn's ulcer: neutrophils highly expressing 5-lipoxygenase were in the utmost surface which bordered the band of cyclooxygenase-2 expression that is located just beneath it, and in the lower layers and below the granulation region were eosinophils carrying 15-lipoxygeanse-1. (2) Cyclooxygenase-2 and 15-Lipoxygenase-1-positive cells formed two barrier-like structures that possibly inhibited neutrophil infiltration.

CONCLUSION

The regulated distribution indicated coordinated interplay between inflammatory cells and parenchymal cells, between arachidonic acid pathways, and between innate and adaptive immunity; and the barrier-like structures indicated protective roles for cyclooxygenase 2 and 15-Lipoxygenase-1 in Crohn's disease.

Biochemical and immunochemical evidences for the presence of lipoxygenase in plant mitochondria

In this paper, both biochemical and immunochemical evidence for the presence of lipoxygenase (LOX) in plant mitochondria is presented. Highly purified pea (Pisum sativum L., cv. Alaska) mitochondria show LOX activity, evaluated as conjugated diene formation, oxygen consumption, and hydroperoxide formation. Both 9- and 13-hydroperoxy-octadecadienoic acids are produced by the oxidation of linoleic acid. LOX activity is particularly evident in swollen mitochondria; it is inhibited by nordihydroguaiaretic acid, a pea anti-LOX B antibody, and has two pH optima (6.0 and 7.5). A mitochondrial protein of approximately 97 kDa cross-reacts with a pea seed anti-LOX B antibody. This reaction is detectable in both soluble (matrix fraction) and membrane-bound (submitochondrial particles) proteins. Considering that pea mitochondria were extracted from actively growing stems that were differentiating tube elements, it is suggested that the presence of LOX in these organelles may be related to their degradation linked to xylem differentiation.

Occurrence of the allene oxide cyclase in different organs and tissues of Arabidopsis thaliana

Occurrence of an essential enzyme in jasmonate (JA) biosynthesis, the allene oxide cyclase, (AOC) was analyzed in different developmental stages and various organs of Arabidopsis thaliana plants by immuno blot analysis and immunocytological approaches. Levels of AOC and of the two preceding enzymes in JA biosynthesis increased during seedling development accompanied by increased levels of JA and 12-oxophytodienoic acid levels after 4 and 8 weeks. Most tissues including all vascular bundles and that of flower buds contain AOC protein. Flowers shortly before opening, however, contain AOC protein preferentially in ovules, stigma cells and vascular bundles, whereas in anthers and pollen AOC could not be detected. The putative roles of AOC and JA in development are discussed.

Oxylipin profiling in pathogen-infected potato leaves

Plants respond to pathogen attack with a multicomponent defense response. Synthesis of oxylipins via the lipoxygenase (LOX) pathway appears to be an important factor for establishment of resistance in a number of pathosystems. In potato cells, pathogen-derived elicitors preferentially stimulate the 9-LOX-dependent metabolism of polyunsaturated fatty acids (PUFAs). Here we show by oxylipin profiling that potato plants react to pathogen infection with increases in the amounts of the 9-LOX-derived 9,10,11- and 9,12,13-trihydroxy derivatives of linolenic acid (LnA), the divinyl ethers colnelenic acid (CnA) and colneleic acid (CA) as well as 9-hydroxy linolenic acid. Accumulation of these compounds is faster and more pronounced during the interaction of potato with the phytopathogenic bacterium Pseudomonas syringae pv. maculicola, which does not lead to disease, compared to the infection of potato with Phytophthora infestans, the causal agent of late blight disease. Jasmonic acid (JA), a 13-LOX-derived oxylipin, accumulates in potato leaves after infiltration with P. syringae pv. maculicola, but not after infection with P. infestans.

Improved amperometric method for the rapid and quantitative measurement of lipoxygenase activity in vegetable tissue crude homogenates

An improved amperometric method for rapid (2 min) quantitative determination of lipoxygenase (LOX) activity in vegetable tissue crude homogenates is presented. Measured LOX activity was linear (R(2) > 0.99) throughout the entire activity range for green bean and for corn below 70% activity. The resolution was 0.4% or 1.11 micromol L(-1) s(-1) of oxygen. The limit of detection was 3.43 micromol L(-1) s(-1) of oxygen. The amperometric method was improved by encapsulating linoleic acid (LA) in beta-cyclodextrin (CD) resulting in a stable substrate-buffer solution at a pH below 8.0. Ethanol and Tween 20 were not effective in solubilizing high LA concentrations required by the assay. A prototype benchtop instrument with the potential for use in an industrial environment is also presented.

Lipoxygenase H1 gene silencing reveals a specific role in supplying fatty acid hydroperoxides for aliphatic aldehyde production

Lipoxygenases catalyze the formation of fatty acid hydroperoxide precursors of an array of compounds involved in the regulation of plant development and responses to stress. To elucidate the function of the potato 13-lipoxygenase H1 (LOX H1), we have generated transgenic potato plants with reduced expression of the LOX H1 gene as a consequence of co-suppression-mediated gene silencing. Three independent LOX H1-silenced transgenic lines were obtained, having less than 1% of the LOX H1 protein present in wild-type plants. This depletion of LOX H1 has no effect on the basal or wound-induced levels of jasmonates derived from 13-hydroperoxylinolenic acid. However, LOX H1 depletion results in a marked reduction in the production of volatile aliphatic C6 aldehydes. These compounds are involved in plant defense responses, acting as either signaling molecules for wound-induced gene expression or as antimicrobial substances. LOX H1 protein was localized to the chloroplast and the protein, expressed in Escherichia coli, showed activity toward unesterified linoleic and linolenic acids and plastidic phosphatidylglycerol. The results demonstrate that LOX H1 is a specific isoform involved in the generation of volatile defense and signaling compounds through the HPL branch of the octadecanoid pathway.

Enzymatic and non-enzymatic lipid peroxidation in leaf development

Enzymatic and non-enzymatic lipid peroxidation has been implicated in programmed cell death, which is a major process of leaf senescence. To test this hypothesis we developed a high-performance liquid chromatography (HPLC) method for a simultaneous analysis of the major hydro(pero)xy polyenoic fatty acids. Quantities of lipid peroxidation products in leaves of different stages of development including natural senescence indicated a strong increase in the level of oxygenated polyenoic fatty acids (PUFAs) during the late stages of leaf senescence. Comprehensive structural elucidation of the oxygenation products by means of HPLC, gas chromatography/mass spectrometry and (1)H nuclear magnetic resonance suggested a non-enzymatic origin. However, in some cases a small share of specifically oxidized PUFAs was identified suggesting involvement of lipid peroxidizing enzymes. To inspect the possible role of enzymatic lipid peroxidation in leaf senescence, we analyzed the abundance of lipoxygenases (LOXs) in rosette leaves of Arabidopsis. LOXs and their product (9Z,11E,13S,15Z)-13-hydroperoxy-9,11,15-octadecatrienoic acid were exclusively detected in young green leaves. In contrast, in senescing leaves the specific LOX products were overlaid by large amounts of stereo-random lipid peroxidation products originating from non-enzymatic oxidation. These data indicate a limited contribution of LOXs to total lipid peroxidation, and a dominant role of non-enzymatic lipid peroxidation in late stages of leaf development.

Characterization of lipoxygenase oxidation products by high-performance liquid chromatography with electron impact-mass spectrometric detection

Lipoxygenase (LOX) is an enzyme that oxygenates polyunsaturated fatty acids to their corresponding hydroperoxy derivatives. For example, LOX found in plants produce the corresponding 13- and 9-hydroperoxide derivatives of linoleic acid (13-HPOD and 9-HPOD). Identification of the HPOD products is usually accomplished by using gas chromatography with mass spectrometric (MS) detection, which requires extensive derivatization of the thermally unstable hydroperoxy group. Here we report a high-performance liquid chromatographic method in combination with electron impact (EI)-MS detection that separates and characterizes the HPOD isomers generated by soybean LOX type I oxygenation of linoleic (LA) and linolenic acids as well as HPOD products produced by photosensitized oxidation of LA. The method does not required derivatization of the hydroxyperoxide group, and location of its position can be determined by the EI-MS fragmentation pattern. The method has been used for the analysis of HPOD produced by action of partially purified LOX from the micro-alga Chlorella pyrenoidosa on LA. The study suggests the presence of two LOX isozymes in the micro-alga that oxygenate LA to its 13-HPOD and 9-HPOD derivatives. Moreover, the 9-LOX isozyme under anaerobic conditions cleaves 13-HPOD to 13-oxo-tridecadienoic acid and pentane but does not cleave 9-HPOD.

Composition of pecan cultivars Wichita and Western Schley [Carya illinoinensis (Wangenh.)K. Koch] grown in Australia

Pecans from the cultivars Wichita and Western Schley [Carya illinoinensis (Wangenh.) K. Koch] collected over three years were analyzed for the following constituents: total lipid content; fatty acid profiles; sucrose content; protein; total dietary fiber; the minerals magnesium, calcium, potassium, sulfur, phosphorus, boron, copper, iron, manganese, sodium, zinc, and aluminum; vitamin C; and lipase and lipoxygenase activities. Year of harvest and cultivar had little effect on the composition of the pecans. Overall, protein content was the only constituent that differed between pecans grown in Australia and those grown in the United States. This difference is probably related to differences in growing location and horticultural practices between the two countries.

Formation by mechanical stimulus of the flavor compounds in young leaves of Japanese pepper (Xanthoxylum piperitum DC.)

The volatile compounds formed in slapped and crushed young leaves of Japanese pepper (Xanthoxylum piperitum DC.) were compared with those of intact leaves by using a dynamic headspace gas analysis combined with GC-MS in an on-line system, together with the results of a sensory evaluation. The results indicated that the factors influencing the aroma note were mainly the constituent oxygenated monoterpenes and C(6) compounds and the quantity of terpene hydrocarbons. To clarify the formation mechanism for the aroma, the activities of lipoxygenase and beta-D-glucosidase were investigated. The results revealed that the hydrolysis of glycosides and the degradation of unsaturated fatty acids both played an important role in the formation of the major aroma compounds in young leaves of Japanese pepper.

Preferential induction of a 9-lipoxygenase by salt in salt-tolerant cells of Citrus sinensis L. Osbeck

Recent findings in our laboratory suggested that in citrus cells the salt induction of phospholipid hydroperoxide glutathione peroxidase, an enzyme active in cellular antioxidant defense, is mediated by the accumulation of hydroperoxides. Production of hydroperoxides occurs as a result of non-enzymatic auto-oxidation or via the action of lipoxygenases (LOXs). In an attempt to resolve the role of LOX activity in the accumulation of peroxides we analyzed the expression of this protein under stress conditions and in cells of Citrus sinensis L. differing in sensitivity to salt. Lipoxygenase expression was induced very rapidly only in the salt-tolerant cells and in a transient manner. The induction was specific to salt stress and did not occur with other osmotic-stress-inducing agents, such as polyethylene glycol or mannitol, or under hot or cold conditions, or in the presence of abscisic acid. The induction was eliminated by the antioxidants dithiothreitol and kaempferol, thus once more establishing a correlation between salt and oxidative stresses. Analyses of both in vitro and in vivo products of LOX revealed a specific 9-LOX activity, and a very fast reduction of the hydroperoxides to the corresponding hydroxy derivatives. This suggests that one of the metabolites further downstream in the reductase pathway may play a key role in triggering defense responses against salt stress.

Colorimetric method for the determination of lipoxygenase activity

A colorimetic assay for lipoxygenase activity has been developed. The assay is based on the detection of the lipoxygenase reaction product, linoleic acid hydroperoxide, by the oxidative coupling of 3-methyl-2-benzothiazolinone (MBTH) with 3-(dimethylamino)benzoic acid (DMAB) in a hemoglobin-catalyzed reaction. This test reaction is rapid and sensitive, and it offers advantages over other methods for detecting lipoxygenase activity. The assay is capable of detecting activity in a number of crude vegetable homogenates and should be particularly useful where a rapid visual determination of lipoxygenase activity is desired.

Changes of specific activity of lipase and lipoxygenase during germination of wheat and barley

Changes of lipase and lipoxygenase specific activities were monitored during wheat and barley germination. Statistically significant correlation (r2 = 0.8148, P < or = 0.02) was found between the specific activities of lipase and lipoxygenase during wheat germination, whereas such correlation did not occur during barley germination.

Qualitative and quantitative analysis of lipoxygenase products in bovine corneal epithelium by liquid chromatography-mass spectrometry with an ion trap

Electrospray ionization ion trap mass spectra of 5-, 12-, and 15-hydroperoxyeicosatetraenoic (HPETE), hydroxyeicosatetraenoic (HETE), and ketoeicosatetraenoic (KETE) acids were recorded. The HPETE were partly dehydrated to the corresponding KETE in the heated capillary of the mass spectrometer. 12-HPETE and 15-HPETE were also converted to KETE by collision-induced dissociation (CID) in the ion trap, whereas CID of 5-HPETE yielded little formation of 5-KETE. Subcellular fractions of bovine corneal epithelium were incubated with arachidonic acid (AA) and the metabolites were analyzed. 15-HETE and 12-HETE were consistently formed, whereas significant accumulation of HPETE and KETE was not detected. Biosynthesis of 12- and 15-HETE was quantified with octadeuterated 12-HETE and 15-HETE as internal standards. The average biosynthesis of 15-HETE and 12-HETE from 30 microM AA by the cytosol was 38 +/- 8 and below 3 ng/mg protein/30 min, respectively, which increased to 78 +/- 21 and 10 +/- 4 ng/mg protein/30 min in the presence of 1 mM free Ca2+. The microsomal biosynthesis was unaffected by Ca2+. The microsomes metabolized AA to 15-HETE as the main metabolite at a low protein concentration (0.3 mg/mL), whereas 12-HETE and 15-HETE were formed in a 2:1 ratio at a combined rate of 0.7 +/- 0.2 microg/mg protein/30 min at a high protein concentration (1.8 mg/mL). The level of 12-HETE in corneal epithelial cells was 50 +/- 13 pg/mg tissue, whereas the endogenous amount of 15-HETE was low or undetectable (<3 pg/mg tissue). Incubation of corneas for 20 min at 37 degrees C before processing selectively increased the amounts of 12-HETE in the epithelium fourfold to approximately 0.2 ng/mg tissue. We conclude that 12-HETE is the main endogenously formed lipoxygenase product of bovine corneal epithelium.

Effects of ozone treatment on postharvest strawberry quality

The effect of ozone treatment on the postharvest quality of strawberry was evaluated. Strawberry fruits (Fragaria x ananassa Duch. cv. Camarosa) were stored at 2 degrees C in an atmosphere containing ozone (0.35 ppm). After 3 days at 2 degrees C, fruits were moved to 20 degrees C to mimic retail conditions (shelf life). The changes in several quality parameters such as fungal decay, color, sugar and acids distribution, and aroma were evaluated during the strawberries' shelf life. Ozone treatment was ineffective in preventing fungal decay in strawberries after 4 days at 20 degrees C. Significant differences in sugars and ascorbic acid content were found in ozone-treated strawberries. At the end of cold storage, the vitamin C content of ozonated strawberries was 3 times that of control fruits. A detrimental effect of ozone treatment on strawberry aroma was observed, with a 40% reduced emission of volatile esters in ozonated fruits.

Volatile components in stored rice [Oryza sativa (L.)] of varieties with and without lipoxygenase-3 in seeds

Lipoxygenase (LOX) is thought to play an important role in the formation of desirable or undesirable flavor and aroma in many plant products. In rice seeds, LOX activity is localized in the bran fraction and LOX-3 is the major isozyme component. We used gas chromatography-mass spectrometry to determine whether the degree of staleness in the flavor of stored brown rice was related to the presence of LOX-3. We found that the amount of hexanal, pentanal, and pentanol in normal raw LOX-3 rice markedly increased during storage at 35 degrees C. That in LOX-3-less rice increased slightly but was a third to a fifth that of normal LOX-3 rice. In cooked rice, the amount of these components from glutinous rice exceeded that in nonglutinous rice, and that in normal LOX-3 rice exceeded that in LOX-3-less rice. These results indicate that the stale flavor production in LOX-3-less rice during storage is less than that in normal LOX-3 rice.

Antisense-mediated depletion of a potato lipoxygenase reduces wound induction of proteinase inhibitors and increases weight gain of insect pests

De novo jasmonic acid (JA) synthesis is required for wound-induced expression of proteinase inhibitors and other defense genes in potato and tomato. The first step in JA biosynthesis involves lipoxygenase (LOX) introducing molecular oxygen at the C-13 position of linolenic acid. We previously have shown that, in potato, at least two gene families code for 13-LOX proteins. We have now produced transgenic potato plants devoid of one specific 13-LOX isoform (LOX-H3) through antisense-mediated depletion of its mRNA. LOX-H3 depletion largely abolishes accumulation of proteinase inhibitors on wounding, indicating that this specific LOX plays an instrumental role in the regulation of wound-induced gene expression. As a consequence, weight gain of Colorado potato beetles fed on antisense plants is significantly larger than those fed on wild-type plants. The poorer performance of LOX-H3-deficient plants toward herbivory is more evident with a polyphagous insect; larvae of beet armyworm reared on the antisense lines have up to 57% higher weight than those fed on nontransformed plants. LOX-H3 thus appears to regulate gene activation in response to pest attack, and this inducible response is likely to be a major determinant for reducing performance of nonspecialized herbivores. However, the regulatory role of LOX-H3 is not caused by its involvement in the wound-induced increase of JA, as wild-type and LOX-H3 deficient plants have similar jasmonate levels after wounding. LOX-H3-deficient plants have higher tuber yields. The apparent effect of suppressing the inducible defensive response on plant vigor suggests that it may pose a penalty in plant fitness under nonstress situations.

An immunoreactive protein to wheat-germ agglutinin antibody is induced in oat roots following invasion of the cereal cyst nematode Heterodera avenae, and by jasmonate

A protein that cross-reacts to a wheat-germ agglutinin antibody was induced in oat roots following the invasion of second-stage juveniles (J2) of the cereal cyst nematode Heterodera avenae. This protein, designated ASP45, was acid soluble, and its molecular mass was about 45 kDa on a sodium dodecyl sulfate-polyacrylamide gel. ASP45 was induced in both compatible and incompatible interactions between the nematode and the plant, and also in roots by exposure to jasmonic acid (JA) or methyl jasmonate. However, ASP45 was not induced by elicitors of pathogenesis-related proteins, abscisic acid, or wounding. Lipoxygenase activity, which is involved in JA synthesis, was higher in nematode-infected and JA-treated roots than in their noninfected, untreated counterparts. Inhibition of lipoxygenase activity in roots abolished ASP45 induction in the nematode-infected roots. Amino acid sequences similar to that of ASP45 were found in chitinases of poplar tree and Arabidopsis, even though ASP45 showed no chitinase activity. Although the biological role of ASP45 in infected roots is not clear, JA is suggested to be involved in signal transduction after pathogen invasion of the plant.

A specific assay for discriminating between peroxidase and lipoxygenase activities

Peroxidases are widespread heme-containing enzymes able to catalyze the oxidation of a large array of organic substrates. There is growing interest in the measurements of peroxidase activity. We noticed that many substrates used in the routine assays for the biological and cytological determinations of peroxidase could be oxidized by lipoxygenase. We found interesting to set up a procedure to detect selectively peroxidase. In the present note, we report a fluorometric test for peroxidase detection using phenolic compounds or hydroxycoumarins.

Quality indices of Jew's mallow and spinach during frozen storage

In this study, Jew's mallow and spinach were heat treated and kept frozen, at -18 degrees C, for 3 months. Analysis of some chemical components and enzymatic activities as well as a sensory evaluation were undertaken. At the end of the storage period, blanched spinach showed no PPO (polyphenyloxidase) activity at all, but still contained PO (peroxydase) and LO (lipoxygenase) activities. The untreated spinach stored under the same conditions showed high activities of PO, PPO and LO. The heat treated mallow still contained high enzyme activities which decreased slowly during frozen storage. Statistical analysis of the chemical composition and the sensory evaluation results indicated that heat treatments of mallow caused significant differences in total solids, pH, chlorophyll a and total chlorophyll, while frozen storage, of samples of the same treatment for 3 months caused no significant differences in moisture, ash, oxalic acid, pH, chlorophyll a and total chlorophyll. No significant differences could be noticed in the overall acceptability between mallow samples mixed with hot water and those mixed with a hot 0.1% MgCO3 solution. Significant differences were found between the heat treated and the untreated mallow. Changes of the chemical composition and the overall acceptability of blanched spinach during frozen storage showed almost the same trend noticed for the Jew's mallow.

Long-term elevation of cyclooxygenase-2, but not lipoxygenase, in regions synaptically distant from spreading depression

Eicosanoids, produced from arachidonic acid by cyclooxygenases (COXs) and lipoxygenases (LIPOXs), are involved in numerous brain processes. To explore if brief and noninjurious stimuli chronically alter expression of these enzymes, we examined the induction of COX-2 and LIPOX expression following unilateral neocortical spreading depression (SD). Expression was examined over time and in regions not experiencing SD (hippocampus) but synaptically connected to the site of stimulation (cortex). One hundred six male Wistar rats had SD induced via microinjection of 0.5 M KCl (0.5 M NaCl for sham) into left parietal cortex every 9 minutes for 1 or 3 hours. One hour before SD some animals received dexamethasone (Dex), mepacrine (Mep), indomethacin (Indo), nordihydroguaiaretic acid (Ndga), phenylephrine (Pe), sodium nitroprusside (Snp) with Pe, or N omega-nitro-L-arginine methyl ester (Lnam). Animals survived for 0, 3, or 6 hours, or 1, 2, 3, 7, 14, 21, or 28 days. Brains were processed immunohistochemically for COX-2 and LIPOX, and the optical density (OD) of the left and right cortex, dentate gyrus (DG), CA3, and CA1 immunoreactivity (IR) were measured. Induction was expressed as the log of left divided by right side OD for each region. COX-2 IR in the left cortex was elevated rapidly and was sustained for 21 days following SD. COX-2 IR was also elevated in the ipsilateral hippocampus not experiencing SD, with the rank order of induction as follows: DG > CA3 > CA1. Dex, Snp, and/or Pe significantly reduced the induction of COX-2. No changes in LIPOX IR were observed. These results show that long-term changes in COX-2 expression are induced by SD and these changes decrease with synaptic distance. Benign stimuli increase COX-2 expression and thus may influence brain function for extended periods and at distant locations.

Arachidonate metabolism in human placenta, fetal membranes, decidua and myometrium: lipoxygenase and cytochrome P450 metabolites as main products in HPLC profiles

Eicosanoids play a key role in pregnancy maintenance and parturition. We investigated the metabolism of arachidonic acid (AA) in short-term tissue cultures of placenta, fetal membranes, decidua and myometrium. Tissues were obtained from caesarean sections before the onset of labour after uncomplicated pregnancies. The released metabolites were analysed by high performance liquid chromatography (HPLC) and specific immunoassays. In radiotracer experiments tissues were labelled with [3H]-AA and metabolites released after incubation with calcium ionophore A23187 were profiled by HPLC. Decidua was more active in metabolizing AA (turnover 34 per cent) than myometrium (28 per cent), placenta (21 per cent) and fetal membranes (17 per cent). Main product in placenta, decidua and myometrium was 12-hydroxyeicosatetraeinoic (12-HETE) (decidua: 19 per cent of released radioactivity, myometrium 14 per cent, placenta 7 per cent). Fetal membranes formed 5-HETE as main product. Another major metabolite in placenta, fetal membranes and decidua was characterized by HPLC as 5(6)-epoxyeicosatrienoic acid. Only myometrium released appreciable amounts of prostaglandins in form of 6-keto-prostaglandin F1 alpha. In non-radioactive experiments formation of eicosanoids from endogenous AA was investigated by HPLC (fluorescence- and UV-detection) and immunoassays. These experiments confirmed the high production of 12-HETE and the low formation of prostaglandins. Our results suggest that the biological role of AA-metabolites, other than prostaglandins, have as yet been underestimated.

Photosynthetic photon flux, photoperiod, and temperature effects on emissions of (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate from lettuce

To investigate the effects of environment on plant volatile emissions, 'Waldmann's Green' leaf lettuce was cultivated under different levels of photosynthetic photon flux (PPF), photoperiod, and temperature. A modified growth chamber was used to sample plant volatile emissions nondestructively, over time, and under controlled conditions. Total volatile emission rates were significantly higher from lettuce cultivated under PPF of 360 or 200 micromoles m-2 s-1 compared to 105 micromoles m-2 s-1, and significantly higher under a 16-h photoperiod than an 8-h photoperiod. No differences were detected among emission rates from different temperature treatments. In controlled environments, emissions could be regulated by adjusting environmental conditions accordingly.

Visible spectrophotometric assay, purification, and molecular properties of a lipoxygenase from eggplant (Solanum melongena Linne) fruits

We purified a lipoxygenase to homogeneity from eggplant (Solanum melongena Linne) fruits employing the established visible spectrophotometric assay, in which the products of the lipoxygenase-catalyzed reaction, hydroperoxyfatty acids, oxidizes 2,2'-azino-di-[3-ethylbenzothiazoline-(6)-sulfonic acid] diammonium salt in the presence of a catalyst cytochrome c to yield chromophores in the visible region. This allowed for the rapid detection of the lipoxygenase activity and was helpful in accomplishing the efficient purification of the lipoxygenase. The purified lipoxygenase was a monomeric enzyme with a molecular weight of 95,000, s20,w of 5.3 S, and an isoelectric point of 4.4. The specific activity and Km value for the linoleate oxygenation were 7.8 mumol min-1 mg-1 and 0.8 mM, respectively, at 25 degrees C and pH 7.0. The enzyme contained 1.3 g-atom of nonheme iron per enzyme.

Variation of iron, copper, free fatty acid content and lipoxygenase activity in peanut kernels subjected to various pretreatments and roasting

Peanut kernels subjected to pretreatment including rehydration, blanching and dehydration, and untreated kernels were roasted at 160 degrees C for times ranging from 0 to 90 min. For both peanuts, the iron content in oil and specific lipoxygenase activity in defatted peanut flour decreased, free fatty acid content increased and copper content changed insignificantly with roasting time. Changes of iron content, lipoxygenase activity and free fatty acid content were more significant in untreated peanuts than in pretreated peanuts. At each roasting time, iron, copper and free fatty acid contents in the oils and lipoxygenase activities in the defatted flours prepared from untreated peanuts were higher than in the oils and flours prepared from pretreated peanuts.

Analysis of lipoxygenase kinetics by high-performance liquid chromatography with a polymer column

Soybean lipoxygenase (LOX; EC 1.12.11.12) catalyzes the oxygenation of polyunsaturated fatty acids, acylglycerols and phosphoglycerols, producing a regio- and enantiospecific hydroperoxide product. The goal of this work was to measure the relative rate of LOX-catalyzed oxidation of mixtures of lipids containing linoleate, using high-performance liquid chromatography (HPLC) and a light-scattering detector (LSD). Previous literature suggested that reversed-phase HPLC with silica-based columns could be used for the separation of individual fatty acids, acylglycerols, phosphoglycerides and their oxidation products. However, these columns produced ineffective separations of phosphoglycerides unless choline chloride and a strong base, such as KOH, are present in the mobile phase. Such modifiers precluded the use of the LSD. It was found that a reversed-phase column based upon an organic polymer support, rather than on silica, was able to separate these mixtures with a ternary solvent gradient of methanol/water/acetonitrile without the need for the addition of modifiers. The oxidation time course of a mixture of linoleic acid, trilinolein and 1-linoleoyl-2-stearoyl-sn-glycero-3-phosphocholine was followed using the developed HPLC method. The results showed that trilinolein and phosphatidylcholine reacted at one-tenth the rate of linoleic acid. The diacylglycerol, 1,3-dilinolein, was oxidized at a rate that was approximately 40% that of linoleic acid, with the formation of mono- and dihydroperoxides as well as other unidentified products.

An octaethylene glycol monododecyl ether-based mixed micellar assay for lipoxygenase acting at neutral pH

Using the detergent octaethylene glycol monododecyl ether (C12E8), a spectrophotometric mixed micellar assay for lipoxygenas (LOX) activity was designed. Potato LOX was able to use the linoleic acid (LA) solubilized in C12E8 micelles, displaying the characteristic induction period of LOX-catalyzed LA peroxidation. In the mixed micellar system, LOX responds to the LA surface concentration expressed as mol% (=[lipid]*100/([detergent]-cmc)) and not to the molarity of the LA. For both potato and soybean LOX, Vmax was independent of the mixed micelle concentration, while Km was independent as well when expressed as mol% but was dependent on C12E8 concentration when expressed in molar. In mixed micelles, H2O2 shortened the induction period, while 13-hydroperoxylinoleic acid and t-butyl hydroperoxide completely removed it. C12E8/LA proved to be a reliable system for assaying LOX activity at pH values around neutrality. Like Tween 20, this system avoided the turbidity problems arising from the protonated fatty acid and did not interfere with the uv-absorption band of the hydroperoxide product. However, this system is superior to the commonly used Tween 20 because it permits investigation of the lipid requirements of LOX since the concentration-independent Km can be determined both in mol% and as the absolute number of lipids per micelle. In addition, the detergent did not affect the enzyme through any side effects.

Synthesis of 12-hydroxyeicosatetraenoic acid by human endometrium and decidua

In order to clarify the possible involvement of lipoxygenase metabolites of arachidonic acid (AA) in implantation, monohydroxylic acid production was examined using human endometrium and decidua in early pregnancy. As 14C-AA was mainly converted to 12-hydroxyeicosatetraenoic acid (12-HETE) as well as prostaglandins (PGs) by the microsomal fraction of the endometrium, a subsequent study was carried out on the endometrium (at various stages) and decidua in early pregnancy using tissue incubation and high performance liquid chromatography (HPLC) analysis for 12-HETE. The amounts of 12-HETE released into the culture medium by proliferative and secretory endometrium were 165.1 +/- 123.4 (ng/mg.protein/24 h, mean +/- SD) and 502.3 +/- 127.2, respectively, whereas, decidua produced a smaller amount of 12-HETE that declined as gestation progressed. This lipoxygenase product as well as PGs might have a role in implantation.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-caused tumor promotion in 7,12-dimethylbenz[a]anthracene-initiated SENCAR mouse skin by a polyphenolic fraction isolated from green tea

Our laboratory has been studying cancer chemopreventive effects of polyphenolic fraction isolated from green tea (GTP). In prior studies we have shown that (a) GTP possesses antigenotoxic effects in various test systems; (b) topical application of GTP protects against UV radiation and chemical carcinogen-induced tumorigenesis in murine skin; and (c) feeding of GTP in drinking water p.o. to mice protects against carcinogen-induced forestomach and lung tumorigenesis. Recently, we showed that in a dose-dependent manner GTP inhibits tumor promoter-caused induction of epidermal ornithine decarboxylase activity in SENCAR mice (R. Agarwal et al., Cancer Res., 52: 3582-3588, 1992). In the present study, we assessed the effect of GTP on TPA-induced skin tumor promotion in 7,12-dimethylbenz(a)anthracene-initiated SENCAR mouse. Topical application of varying doses of GTP (1-24 mg) 30 min prior to that of each TPA application resulted in highly significant protection against skin tumor promotion in a dose-dependent manner. The animals pretreated with GTP showed substantially lower tumor body burden such as decrease in total number of tumors per group, number of tumors per animal, tumor volume per mouse, and average volume per tumor, as compared to the animals that did not receive GTP. Since TPA-induced epidermal cyclooxygenase and lipoxygenase activities and edema and hyperplasia are conventionally used markers of skin tumor promotion, we also assessed the effect of preapplication of GTP on these parameters. As quantitated by the formation of prostaglandin and hydroxy-eicosatetraenoic acid metabolites from, respectively, cyclooxygenase- and lipoxygenase-catalyzed metabolism of arachidonic acid, skin application of GTP to SENCAR mice resulted in significant inhibition of TPA-caused effects on these 2 enzymes. Prior application of GTP to mouse skin also resulted in 30-46% inhibition of TPA-induced epidermal edema and hyperplasia. The results of the present study suggest that GTP possesses anti-skin tumor-promoting effects, and that the mechanism of such effects may involve inhibition of tumor promoter-induced epidermal ornithine decarboxylase, cyclooxygenase and lipoxygenase activities, edema, and hyperplasia. Further studies are in progress to define which component present in GTP is responsible for its anti-skin tumor-promoting effects.

Screening soybean (grain and vegetable) genotypes for nutrients and anti-nutritional factors

Fifty six genotypes of grain-type soybean and 17 genotypes of vegetable-type soybean collections were analyzed for protein and oil content, trypsin inhibitor, and lipoxygenase activities. The protein and oil content ranged from 36.9 to 47.9% and from 13.3 to 23.0% for different accessions in grain- and vegetable-type soybeans, respectively. Trypsin inhibitor and lipoxygenase activities ranged from 22.0 to 47.0 trypsin inhibitor units/mg meal and from 482 to 6265 lipoxygenase units/min/mg meal for grain- and vegetable-type soybeans, respectively. Significant correlations (r = -0.62 and -0.52, P less than 0.05) were found between protein and oil, and between protein and trypsin inhibitor. A significant positive correlation (r = 0.42, P less than 0.05) was also calculated for oil and lipoxygenase activity. Several genotypes of soybean and vegetable soybean (plant introductions 423905, 417330, 417223, 171451, 200506, 200523, 417124, 227687, 203402, 445842, 203399, 423852, 416771, FC 31927, Avoyelles, and Sooty) showed good nutritional potential and may be useful in a breeding program to improve the nutritional quality of soybean. Screening for essential amino acids, fatty acids, and trace minerals for selected genotypes is underway.

An aldehyde-containing galactolipid from the red alga Gracilariopsis lemaneiformis

An unprecedented aldehyde-containing digalactosyldiacylglycerol (DGDAG) has been isolated from the red alga Gracilariopsis lemaneiformis and structurally defined. Its structure was determined as 1-O-[5-hydroxy-12-oxo-dodeca-6(E),8(E),10(E)-trienoyl]-2-O-p almitoyl-3-O- [-beta-D-galactopyranosyl-6,1-alpha-D-galactopyranosyl]-glycerol by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry and degradation to simple fragments. The identification of this aldehyde-containing DGDAG from G. lemaneiformis, in addition to our previous findings of unusual galactolipids, further indicates that this alga has unique lipoxygenase capacities.

Assay of liver cytosol lipoxygenase by differential pulse polarography

Lipoxygenase activity assayed by differential pulse polarography was found to be more sensitive than that determined by the increase in absorption at 234 nm. The lipoxygenase activity level in the liver cytosol of rats fed oxidized palm oil was significantly higher than that of the control animals fed either saline or fresh palm oil. The effects of flavonoids on the inhibition of lipoxygenase activity level in liver cytosol of rats were in the decreasing order quercetin greater than myricetin greater than morin greater than phloretin. The observed free malonaldehyde (MDA) in liver cytosol of rats determined by high-performance liquid chromatography using malonaldehyde-dinitro-phenylhydrazine complex was 23, 25, and 51.2% for rats fed saline, fresh palm oil, and oxidized palm oil, respectively. A linear relationship between the lipoxygenase activity and the free liver cytosol MDA was shown. The assay of lipoxygenase by differential pulse polarography provides a simple, sensitive, and quantitative method for the study of liver lipid peroxidation.

Preparation and characterization of monoclonal antibodies against soybean seed lipoxygenase isoenzymes

Sets of monoclonal antibodies have been prepared using two soybean seed lipoxygenase isoenzymes as the antigens. The antibodies were characterized by ELISA, Western blot analysis, immunoprecipitation, and in kinetic assays. Several antibodies displaying selectivity for the two closely related polypeptides were obtained, while the majority of the antibodies generated were crossreactive. Antibodies specific to the native and denatured forms of the two proteins were also obtained. Two of the monospecific antibodies were shown to immunoprecipitate the appropriate isoenzyme selectively from a mixture. When these antibodies were immobilized on agarose, they were successful in the immunoaffinity purification of the individual isoenzymes. In kinetic experiments certain antibodies were found to influence catalysis upon incubation with lipoxygenase. Antibodies which both inhibited and stimulated catalysis were identified.

Altered arachidonic acid metabolism during differentiation of the human monoblastoid cell line U937

The human cell line U937 was used as a model for differentiation along the mononuclear phagocyte lineage. Following treatment with the phorbol ester TPA, PGE2 and TxB2 secretion was induced 50-100-fold, and both PGF2 alpha and PGI2 levels became detectable in the supernatant of TPA-differentiated U937 cells. The content of the prostaglandin precursor, arachidonic acid, remained unchanged in the cellular phospholipids of undifferentiated and TPA-differentiated U937 cells. Of the enzymes involved in the availability and metabolism of arachidonic acid, phospholipase A2 activity was increased 2-fold in the membranes of TPA-differentiated U937 cells, whereas lysophosphatide acyltransferase activity remained unaltered. Cyclooxygenase activity, however, was enhanced 5-10-fold, which was due to enhanced expression of the enzyme as demonstrated by dot-blot analysis. The data suggest that the capacity to secrete prostaglandins is acquired during differentiation with TPA and results mainly from an increased cyclooxygenase activity. Despite the capacity of TPA-differentiated U937 cells to synthesize prostaglandins, none of the known monocytic stimuli further stimulated prostaglandin secretion in TPA-differentiated U937 cells. Generation of leukotrienes appears to represent a later state in the differentiation along the monocyte-macrophage lineage, since neither LTB4 nor cysteinyl-leukotrienes were detectable in the supernatants of either undifferentiated or TPA-differentiated U937 cells.

Arachidonic acid metabolism in HEL/30 murine epidermal cell line

The established mouse epidermis-derived cell line HEL/30 was incubated in the presence of 3H arachidonic acid (AA) for 1 h. After medium removal, cells were reincubated with fresh medium in the presence or absence of the calcium ionophore A23187 and tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). The AA metabolites formed were extracted from cell-free medium and analyzed using TLC and HPLC. The distribution of the recovered radioactivity showed PGE2, 15-hydroxy-eicosatetraenoic acid (15-HETE), and leukotriene B4 (LTB4), as major products of AA metabolism. The presence of calcium ionophore A23187 increased the release of radioactivity, without affecting the profile of metabolites present in the medium. TPA elicited a preferential increase of cycloxygenase metabolism, this effect being reversed by indomethacin. 5,8,11,14-eicosatetraynoic acid (ETYA) almost completely inhibited LT and HETE formation in A23187 and TPA-treated cells. The results show that HEL/30 cells are able to metabolize AA via both cyclo- and lipoxygenase pathways and that these activities can be modified by chemical means. This cell line might be a suitable tool for studying the involvement of arachidonic acid cascade in cell response to exogenous stimuli.

[A coupled enzyme system for detection of phospholipase A2 inhibitors]

A coupled assay of phospholipase-A2 and lipoxygenase that especially can be applied to the determination of phospholipase-A2-inhibition is described. A partialsynthetic dilinolenoylglycerophosphocholine is used as substrate in the form of mixed micelles with Twenn-20. Pentadienoic fatty acids primarily produced by venom phospholipase-A2 are peroxydized in a second step quantitatively. Diminution in oxygen content is registrated by an oxygen sensitive electrode and the reaction process is plotted continuously. The usefulness of this assay in the screening of inhibitors and disturbing influences are discussed.

Primary structure of soybean lipoxygenase-1

The primary structure of lipoxygenase-1 from soybeans has been determined. The results were deduced from the nucleotide sequence of the complete cDNA for isozyme lipoxygenase-1 and were confirmed by Edman sequencing of selected peptides obtained by CNBr cleavage and supported by carboxyl-terminal sequencing of the intact protein and by partial peptide analysis employing fast atom bombardment-mass spectroscopy. The enzyme has a molecular weight of 94,038 based on its content of 838 amino acids.