An anaerobic reaction between lipoxygenase, linoleic acid and its hydroperoxides

In an anaerobic system soya-bean lipoxygenase together with linoleic acid induces a structural rearrangement of 13-hydroperoxyoctadeca-cis-9-trans-11-dienoic acid leading to the formation of 13-oxotrideca-cis(trans)-9-trans-11-dienoic acid and n-pentane as well as 13-oxo-octadeca-9,11-dienoic acid. It is proposed that the 13-peroxyoctadeca-cis-9-trans-11-dienoic acid radical formed through hydrogen radical abstraction by the linoleic acid radical is the key intermediate for these reactions.     

Large-scale preparation of (9Z,12E)-[1-(13)C]-octadeca-9,12-dienoic acid, (9Z,12Z,15E)-[1-(13)C]-octadeca-9,12,15-trienoic acid and their [1-(13)C] all-cis isomers

Several grams of labelled trans linoleic and linolenic acids with high chemical and isomeric purities (>97%) have been prepared for human metabolism studies. A total of 12.5 g of (9Z, 12E)-[1-(13)C]-octadeca-9,12-dienoic acid and 6.3 g of (9Z,12Z, 15E)-[1-(13)C]-octadeca-9,12,15-trienoic acid were obtained in, respectively, seven steps (7.8% overall yield) and 11 steps (7% overall yield) from 7-bromo-heptan-1-ol. The trans bromo precursors used for the labelling were synthesised by using copper-catalysed couplings. The trans fatty acids were then obtained via the nitrile derivatives. A total of 23.5 g of (9Z,12Z)-[1-(13)C]-octadeca-9, 12-dienoic acid and 10.4 g of (9Z,12Z,15Z)-[1-(13)C]-octadeca-9,12, 15-trienoic acid were prepared in five steps in, respectively, 32 and 18% overall yield. Large quantities of bromo and chloro precursors were synthesised from the commercially available acid according to Barton's procedure. In all cases, the main impurities (>0.5%) of each labelled fatty acid have been characterised.     

The molecular and crystal structures of 4-N-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-l-asparagine trihydrate and 4-N-(β-d-glucopyranosyl)-l-asparagine monohydrate. The X-ray analysis of a carbohydrate–peptide linkage

X-ray analyses have shown that the glucopyranose rings of GlcNAc-Asn [4-N-(2-acetamido-2-deoxy-beta-d-glucopyranosyl)-l-asparagine] and Glc-Asn [4-N-(beta-d-glucopyranosyl)-l-asparagine] both have the C-1 chair conformation and also that the glucose-asparagine linkage of each molecule is present in the beta-anomeric configuration. The dimensions (the estimated standard deviations of the last digit are in parentheses) of the glycosidic bond in GlcNAc-Asn and Glc-Asn are, respectively, C((1))-N((1)) 0.1441(6)nm, 0.146(2)nm; angle O((5))-C((1))-N((1)) 106.8(3) degrees , 105.7(8) degrees ; angle C((2))-C((1))-N((1)) 111.1(4) degrees , 110.4(9) degrees ; angle C((1))-N((1))-C((9)) 121.4(4) degrees , 120.5(9) degrees . The glycosidic torsion angle C((9))-N((1))-C((1))-C((2)) is 141.0 degrees and 157.6 degrees in GlcNAc-Asn and Glc-Asn respectively. Hydrogen-bonding is extensive in these two crystal structures and does affect one torsion angle in particular. Two very different values of chi(1)(N-C(alpha)-C(beta)-C(gamma)) occur for the asparagine residue of the two different molecules; the values of chi(1), -69.0 degrees in GlcNAc-Asn and 61.9 degrees in Glc-Asn, correspond to two different staggered conformations about the C(alpha)-C(beta) bond as the NH(3) (+) group is adjusted to different hydrogen-bonding patterns. The two trans-peptide groups in GlcNAc-Asn show small distortions in planarity whereas that in Glc-Asn is more non-planar. The mean plane through the atoms of the amide group at C((2)) in GlcNAc-Asn is approximately perpendicular (69 degrees ) to the mean plane through the C((2)), C((3)), C((5)) and O((5)) atoms of the glucose ring and that at C((1)) is less perpendicular (65 degrees ). The mean plane through the atoms of the amide group in Glc-Asn makes an angle of only 55 degrees with the mean plane through these same four atoms of the glucose ring. The N((1))-H bond of the amide at C((1)) is trans to the C((1))-H bond in these two compounds; the N((2))-H bond of the amide at C((2)) is trans to the C((2))-H bond in GlcNAc-Asn. The values of the observed and final calculated structure amplitudes have been deposited as Supplementary Publication SUP 50035 (26 pages) at the British Library (Lending Division), (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1973) 131, 5.     

The enzymic conversion of linoleic acid into 9-(nona-1′,3′-dienoxy)non-8-enoic acid, a novel unsaturated ether derivative isolated from homogenates of Solanum tuberosum tubers

1. A major component of the lipids in aqueous (pH7.5) homogenates of tuber tissue from Solanum tuberosum was isolated and characterized as 9-(nona-1',3'-dienoxy)non-8-enoic acid. 2. This novel unsaturated ether fatty acid derivative, which contains a butadienylvinyl ether function, has the structure: [Formula: see text] and is formed from linoleic acid by a sequence of enzymic reactions. 3. A precursor of the unsaturated ether derivative is 9-d-hydroperoxyoctadeca-10,12-dienoic acid, formed by the action of S. tuberosum lipoxygenase on linoleic acid. 4. An enzyme that converts the fatty acid hydroperoxide into the unsaturated ether derivative was isolated from S. tuberosum. The pH optimum of this enzyme is approx. 9, although the overall conversion of linoleic acid into the ether derivative is maximal at pH7.5. 5. An unusual feature of this pathway is the insertion of an oxygen atom into the alkyl chain of a fatty acid. 6. This novel mechanism may play a role in the breakdown of polyunsaturated fatty acids to volatile products in plants.     

Relationship between temporary inhibition and structure of disulfide-linkage analogs of marinostatin, a natural ester-linked protein protease inhibitor.

A 12-residue marinostatin [MST(1-12): (1)FATMRYPSDSDE(12)] which contains two ester linkages of Thr(3)-Asp(9) and Ser(8)-Asp(11) strongly inhibits subtilisin. In order to study the relationship between the inhibitory activity, structure, and stability of MST, MST analogs were prepared by changing ester linkages to a disulfide linkages. The analogs without the disulfide linkage between 3 and 9 positions lost their inhibitory activity. The K(i) value of 1SS(C(3)-C(9)) ((1)FACMRYPSCSDE(12)), which has a single disulfide linkage of Cys(3)-Cys(9) was comparable with those of MST(1-12) and MST-2SS ((1)FACMRYPCCSCE(12)), a doubly linked analog of Cys(3)-Cys(9) and Cys(8)-Cys(11). However, 1SS(C(3)-C(9)) and MST-2SS showed temporary inhibition, but not MST(1-12): These analogs were inactivated after incubation with subtilisin for 30 min, and were specifically hydrolyzed at the reactive site. (1)H NMR study showed that 1SS(C(3)-C(9)) has two conformations, which contain a cis- (70%) or trans- (30%) Pro residue, while MST-2SS as well as MST(1-12) takes a single conformation containing only a cis-Pro residue. Hydrogen-deuterium exchange rate of the Arg(5) (P1') NH proton of the MST analogs was about 100 times faster than that of MST(1-12). These results indicate that the linkage between the positions 8 and 11 plays a role for fixing the cis-conformation of the Pro(7) residue, and that the linkage between 3 and 9 is indispensable for the inhibition, but not enough for stable protease-inhibitor complex.     

An Enzymatic Conversion of Lipoxygenase Products by a Hydroperoxide Lyase in Blue-Green Algae (Oscillatoria sp.)

An enzyme has been isolated from blue-green algae Oscillatoria sp. which utilizes the product, 13-hydroperoxy-9, 11-octadecadienoic acid (13-HPOD), of lipoxygenase for its substrate. This enzyme, termed hydroperoxide lyase, converts the conjugated diene 13-hydroperoxide of linoleic acid to 13-oxotrideca-9, 11-dienoic acid. The structure of the latter has been determined by ultraviolet spectroscopy and mass spectrometry. 9-HPOD is not a substrate for this enzyme. The hydroperoxide lyase from Oscillatoria sp. has a maximum of activity at pH 6.4 and 30°C. The molecular weight of the enzyme was estimated at 56,000. The enzyme was not inhibited by BW 755C, but was inhibited by molecules containing more than one hydroxyl group. Quercetin was found to be the best inhibitor of the enzyme activity. The purified hydroperoxide lyase from Oscillatoria sp. showed an apparent K_m of 7.4 micromolar and a V_max of 35 nanomoles per minute per milligram of protein for 13-HPOD. An enzymatic pathway for the biogenesis of oxodienoic acid from linoleic acid is proposed. This involves the sequential activity of lipoxygenase and hydroperoxide lyase enzymes.     

Quantitative deuterium isotopic profiling at natural abundance indicates mechanistic differences for delta 12-epoxidase and delta 12-desaturase in Vernonia galamensis

Quantitative (2)H NMR spectroscopy can determine the natural abundance ((2)H/(1)H) ratio at each site of a molecule. In natural products, variation in these values is related to the reaction mechanisms in the pertinent biosynthetic pathway. For the first time, this novel approach has been exploited to probe for mechanistic differences in the introduction of different functionalities into a long-chain fatty acid. Vernolic acid, a major component of the seed oil of Vernonia galamensis, contains both an epoxide and a desaturation. The site-specific isotopic distribution ((2)H/(1)H)(i) has been determined for both vernolic acid and linoleic acid isolated from the same V. galamensis oil. It is found that the ((2)H/(1)H) ratio of vernolic acid shows a pattern along the entire length of the chain, consistent with linoleic acid being its immediate precursor. Notably, the C13 relates to the C13 of linoleic acid but not to the C13 of oleic acid. Furthermore, the C12 and C13 positions in vernolic acid are less depleted, consistent with a change in hybridization state from sp(2) to sp(3). However, the C11 position shows a marked relative enrichment in the vernolic acid, implying that it plays a role in the epoxidase but not the desaturase mechanism. Thus, although it can be concluded that the catalytic mechanisms for the epoxidase and desaturase activities are similar, marked differences in the residual ((2)H/(1)H) patterns indicate that the reaction mechanisms are not identical.     

Co-oxidation of carotenes requires one soybean lipoxygenase isoenzyme.

The type II lipoxygenase (optimum pH 6.5) from soybeans was purified and separated into two fractions either by chromatography on DEAE-Sephadex or by isoelectric focusing. In the presence of linoleic acid and oxygen both fractions co-oxidise canthaxanthine or beta-carotene as effectively as a combination of these fractions. Oxygenation of linoleic acid and co-oxidation of canthaxanthine by type II lipoxygenase is stimulated by 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid but not by 13-hydroxy-cis-9,trans-11-octadecadienoic acid or 9-hydroperoxy-trans-10,cis-12-octadecadienoic acid.     

Biomimetic nitration of the linoleic acid metabolite 13-hydroxyoctadecadienoic acid: isolation and spectral characterization of novel chain-rearranged epoxy nitro derivatives

Nitration of unsaturated fatty acids is a (patho)physiologically important pathway of lipid modification induced by nitric oxide-derived species. We report herein on the unexpected chain rearrangement undergone by (13S,9Z,11E)-13-hydroxyoctadeca-9,11-dienoic acid (1), a linoleic acid metabolite, when exposed to nitrating agents of biological relevance. At pH 7.4 and at room temperature, reaction of 1 with peroxynitrite (ONOO-) as well as Fe2+-EDTA/H2O2/NO2- and horseradish peroxidase/H2O2/NO2- led to the formation of two nitration products, which could be isolated as the methyl esters and were identified as diastereoisomeric methyl (12S)-10,11-epoxy-12-hydroxy-9-nitromethylheptadecanoates by extensive 1H, 13C, 15N NMR and MS analysis.     

New conjugated hydroxydienoic fatty acids and acetotriacylglycerols from Securidaca longipedunculata seed oil.

Like other members of the plant family Polygalaceae, Securidaca longipedunculata Fres., is a source of fatty acids and triacylglycerols with unusual structures. Its seed oil contains at least seven chromatographically distinct groups of triacylglycerols divided into two series: One series represents monoacetotriacylglycerols, and the other 'normal' triacylglycerols having only long-chain fatty acids. Each series has groups containing zero, one or two conjugated hydroxydienoic acids. In addition, there is a small amount of triacylglycerol incorporating three hydroxy acids. In addition to coriolic (13-hydroxyoctadeca-cis-9,trans-11-dienoic) acid (27%), two of its previously unknown homologs are present: 11-hydroxyhexadeca-cis-7,trans-9-dienoic acid (15%) and 9-hydroxytetradeca-cis-5,trans-7-dienoic acid (2%).     

Sex-related differences in desaturation and chain elongation of essential fatty acids studied in isolated rat hepatocytes

When [14C]linoleic acid (18:2(n-6)) or [14C]dihomogammalinolenic acid (20:3(n-6)) was incubated with isolated liver cells from rats fed an essential fatty acid deficient diet, delta 6- and delta 5-desaturation, chain elongation and synthesis of 14C-labelled C14-C18 fatty acids (from [14C]acetate) were enhanced in female cells compared with male ones. No sex difference in total secretion of very low density lipoproteins (VLDL) was observed. However, VLDL secreted from female cells contained significantly more C16-C18 fatty acids than male cells. It is suggested that the observed sex differences, at least in part, may be related to the different content of fatty acid binding proteins in female cells compared with males.     

Design and syntheses of putative bioactive taxanes

Reduction of 5 alpha-hydroxy-7 beta,9 alpha,10 beta-triacetoxy-4(20), 11(12)-taxadien-13-one 1 with activated zinc in glacial acetic acid led to rearranged products, including compounds with double bonds at C3-C4, C10-C11 or with an epoxide at C11-C12. Molecular modeling studies suggested that addition of a side chain at C-20 or C-5 of the taxanes with a C3-C4 double bond might lead to bioactivity. Semi-syntheses and results of bioactivities are discussed.     

A linoleic acid (8R)-dioxygenase and hydroperoxide isomerase of the fungus Gaeumannomyces graminis. Biosynthesis of (8R)-hydroxylinoleic acid and (7S,8S)-dihydroxylinoleic acid from (8R)-hydroperoxylinoleic acid.

The fungus Gaeumannomyces graminis metabolized linoleic acid extensively to (8R)-hydroperoxylinoleic acid, (8R)-hydroxylinoleic acid, and threo-(7S,8S)-dihydroxylinoleic acid. When G. graminis was incubated with linoleic acid under an atmosphere of oxygen-18, the isotope was incorporated into (8R)-hydroxylinoleic acid and 7,8-dihydroxylinoleic acid. The two hydroxyls of the latter contained either two oxygen-18 or two oxygen-16 atoms, whereas a molecular species that contained both oxygen isotopes was formed in negligible amounts. Glutathione peroxidase inhibited the biosynthesis of 7,8-dihydroxylinoleic acid. These findings demonstrated that the diol was formed from (8R)-hydroperoxylinoleic acid by intramolecular hydroxylation at carbon 7, catalyzed by a hydroperoxide isomerase. The (8R)-dioxygenase appeared to metabolize substrates with a saturated carboxylic side chain and a 9Z-double bond. G. graminis also formed omega 2- and omega 3-hydroxy metabolites of the fatty acids. In addition, linoleic acid was converted to small amounts of nearly (65% R) racemic 10-hydroxy-8,12-octadecadienoic acid by incorporation of atmospheric oxygen. An unstable metabolite, 11-hydroxylinoleic acid, could also be isolated as well as (13R,13S)-hydroxy-(9E,9Z), (11E)-octadecadienoic acids and (9R,9S)-hydroxy-(10E), (12E,12Z)-octadecadienoic acids. In summary, G. graminis contains a prominent linoleic acid (8R)-dioxygenase, which differs from the lipoxygenase family of dioxygenases by catalyzing the formation of a hydroperoxide without affecting the double bonds of the substrate.     

Studies on polyenoic acid incorporation into human platelet lipid stores: interactions with linoleic and arachidonic acids

Several polyunsaturated fatty acids (C18-C22 acids) have been compared in their uptake by human platelets and their acylation into glycerophospholipid subclasses. This was also studied in the presence of linoleic and/or arachidonic acids, the main fatty acids of plasma free fatty acid pool. Amongst C20 fatty acids, dihomogamma linolenic acid (20:3(n-6)), 5,8,11-icosatrienoic acid (20:3(n-9)) and arachidonic acid (20:4(n-6)) were better incorporated. The uptake of 5,8,11,14,17-icosapentaenoic acid (20:5(n-3)) was significantly lower and comparable to that of C22 fatty acids (7,10,13,16-docosatetraenoic acid (22:4(n-6)) and 4,7,10,13,16,19-docosahexaenoic acid (22:6(n-3)) and linoleic acid (18:2(n-6)). In this respect, linolenic acid (18:3(n-3)) appeared the poorest substrate. The bulk of each acid was acylated into glycerophospholipids although the presence of linoleic and/or arachidonic acids diverted a part towards neutral lipids. This was prominent for 18:3(n-3) and C22 fatty acids. The glycerophospholipid distribution of each acid differed substantially and was not affected by the presence of linoleic and or arachidonic acids, except for 18:3(n-3) and 22:6(n-3) that were strongly diverted towards phosphatidylethanolamine (PE) at the expense of phosphatidylcholine (PC). The main features were an efficient acylation of 20:3(n-9) into phosphatidylinositol (PI) followed by 20:3(n-6) and 20:4(n-6), then by 20:5(n-3) and 22:4(n-6), and finally 22:6(n-3) and C18 fatty acids. This was reciprocal to the acylation into PE and to a lesser extent into PC which remained the main storage species in all cases. We conclude that human platelets may exhibit a certain specificity for taking up polyunsaturated fatty acids both in terms of total uptake and glycerophospholipid subclass distribution. Also the presence of polyunsaturated fatty acids of normal plasma, like linoleic and arachidonic acids, may interact specifically with such an uptake and distribution.     

Optimization of Large Scale Preparation of 13-(S)-Hydroperoxy-9Z, 11E-Octadecadienoic Acid Using Soybean Lipoxygenase. Application to the Chemoenzymatic Synthesis of (+)-Coriolic Acid

The optimization of 13-S-hydroperoxy-9Z, 11E-octadecadienoic acid synthesis is described using lipoxygenase-1 from soybeans at high substrate concentration. The optimal values of the tested parameters are as follows: oxygen pressure 2.5 bar, temperature 5°C, pH 11, enzyme concentration 4 mg/ml and substrate concentration 0.1 M. All these values were used in a single reaction, allowing chemoenzymatic synthesis of gram amounts of (+)-coriolic acid (99%, e.e. 97%) with a 54% yield starting from linoleic acid.     

Thiafatty acids as tracers to investigate biosynthetic pathways of lepidopteran sex pheromones

In order to investigate the potential utility of thiafatty acids as tracers for biosynthetic studies of moth sex pheromones, a series of thiatetradecanoic acids, namely 8-, 9-, 10-, 11-, 12- and 13-thiatetradecanoic, were prepared and their metabolism was investigated in pheromone glands of Spodoptera littoralis. Analysis by gas chromatography coupled to mass spectrometry of extracts from pheromone glands treated with the above acids showed that only 8-thiatetradecanoic acid and 13-thiatetradecanoic acid were metabolized by desaturation and were incorporated into the sex pheromone biosynthetic pathway. 13-Thiatetradecanoic acid was converted into (E)- and (Z)-13-thiatetradec-11-enoic acids, (Z,E)-13-thiatetradeca-9,11-dienoic acid, 11-thiadodecanoic acid, (E)- and (Z)-11-thiadodec-9-enoic acids and 15-thiahexadecanoic acid. 8-Thiatetradecanoic acid gave rise to two monoenoic thiafatty acids and two dienoic thiafatty acids, which were assigned to (Z)- and (E)-8-thiatetradec-11-enoic acids, (Z,E)-8-thiatetradeca-9,11-dienoic acid and (E,E)-8-thiatetradeca-10,12-dienoic acid. The other thiafatty acids tested, 9-, 10-, 11- and 12-thiatetradecanoic acids, were not metabolized by desaturation, although the corresponding products of beta-oxidation and chain elongation were detected. The occurrence of sulfoxides was not detected in this case, in disagreement with results on the metabolism of some thiaacids previously reported by other authors in yeast, Saccharomyces cerevisiae.     

In vitro antiplasmodial investigation of medicinal plants from El Salvador

In vitro antiplasmodial activities of extracts from Albizia saman, Fabaceae, Calea tenuifolia (C. zacatechichi), Asteraceae, Hymenaea courbaril, Fabaceae, Jatropha curcas, Euphorbiaceae, Momordica charantia, Cucurbitaceae, and Moringa oleifera, Moringaceae were evaluated. From the lipophilic extract of C tenuifolia five active flavones were obtained. 4',5-Dihydroxy-7-methoxyflavone [genkwanin] and 5-hydroxy-4',7-dimethoxyflavone [apigenin 4',7-dimethylether] exhibited the strongest antiplasmodial activity against a chloroquine-sensitive strain (poW) and a chloroquine-resistant strain (Dd2) of Plasmodium falciparum [IC50 values: 17.1-28.5 microM). Furthermore octadeca-9,12-dienoic acid [linoleic acid] [IC50] values of 21.8 microM (poW) and 31.1 microM (Dd2)] and octadeca-9,12,15-trienoic acid (alpha-linolenic acid) were isolated.     

Sequential substitution of 1,2-dichloro-ethene: a convenient stereoselective route to (9Z,11E)-, (10E,12Z)- and (10Z,12Z)-

Conjugated linoleic acid (CLA) isomers are present in human foods derived from milk or ruminant meat. To study their metabolism, (9Z,11E)-, (10E,12Z)- and (10Z,12Z)-[1-(14)C]-octadecadienoic acids with high radiochemical and isomeric purities (>98%) were prepared by stereoselective multi-step syntheses involving sequential substitution of 1,2-dichloro-ethene. In the case of the (9Z,11E) isomer, a first metal-catalyzed cross-coupling reaction between (E)-1,2-dichloro-ethene and 2-non-8-ynyloxy-tetrahydro-pyran, obtained from 7-bromo-heptan-1-ol, gave a conjugated chloroenyne. A second coupling reaction with hexylmagnesium bromide provided a heptadecenynyl derivative. Stereoselective reduction of the triple bond and bromination afforded (7E,9Z)-17-bromo-heptadeca-7,9-diene. Formation of the Grignard reagent and carbonation with 14CO(2) gave (9Z,11E)-[1-(14)C]-octadeca-9,11-dienoic acid (overall yield from 7-bromo-heptan-1-ol, 14.4%). (10E,12Z)- and (10Z,12Z)-[1-(14)C]-octadeca-10,12-dienoic acids were synthesized by the same methodology using 1-heptyne, 8-bromo-octan-1-ol and, respectively, (E)-1,2-dichloro-ethene and its (Z) isomer (overall yield from 8-bromo-octan-1-ol, 13.1% (10E,12Z); 17.2% (10Z,12Z)). Impurities (<2% if present) were identified as being (E,E) CLA isomers and were removed by RP-HPLC. Metabolism studies in animal are in progress.     

Self-inactivation by 13-hydroperoxylinoleic acid and lipohydroperoxidase activity of the reticulocyte lipoxygenase

1. The self-inactivation of lipoxygenase from rabbit reticulocytes with linoleic acid at 37 degrees C is caused by the product 13-hydroperoxylinoleic acid. This inactivation is promoted by either oxygen or linoleic acid. 2. Lipohydroperoxidase activity was demonstrated with 13-hydroperoxylinoleic acid plus linoleic acid as hydrogen donor under anaerobic conditions at 2 degrees C. The products were 13-hydroxylinoleic acid, oxodienes and compounds of non-diene structure similar to those produced by soybean lipoxygenase-1. 3. 13-Hydroperoxylinoleic acid also changed the absorbance and fluorescence properties of reticulocyte lipoxygenase. The results indicate that one equivalent of 13-hydroperoxylinoleic acid converts the enzyme from the ferrous state into the ferric state as described for soybean lipoxygenase-1. The spectral changes were reversed by sodium borohydride at 2 degrees C, but not at 37 degrees C; it is assumed that the ferric form of reticulocyte lipoxygenase suffers inactivation.     

Lipoxygenase from potato tubers. Partial purification and properties of an enzyme that specifically oxygenates the 9-position of linoleic acid

A lipoxygenase (EC 1.13.1.13) was partially purified from potato tubers and was shown to differ from previously characterized soya-bean lipoxygenases in the positional specificity and pH characteristics of the oxygenation reaction. The potato enzyme converted linoleic acid almost exclusively (95%) into 9-d-hydroperoxyoctadeca-trans-10,cis-12-dienoic acid. The 13-hydroperoxy isomer was only a minor product (5%). Linolenic acid was an equally effective substrate, which was also oxygenated specifically at the 9-position. The enzyme had a pH optimum at 5.5-6.0 and was inactive at pH9.0. A half-maximal velocity was obtained at a linoleic acid concentration of 0.1mm. No inhibition was observed with EDTA (1mm) and cyanide (1mm) or with p-chloromercuribenzoate (0.2mm). Haemoproteins were not involved in the lipoxygenase activity. The molecular weight of the enzyme was estimated from gel filtration to be approx. 10(5). Preliminary evidence suggested that the enzyme oxygenated the n-10 position of fatty acids containing a penta(n-3, n-6)diene structure.