The heterogeneity of soyabean lipoxygenase

New C16 fatty-acid-based oxylipin pathway in the marine diatom Thalassiosira rotula

An unprecedented series of C16 oxylipins (1-8) has been characterized from the marine diatom Thalassiosira rotula. Absolute stereochemistry of the major alcohols 1 and 3 was determined to be 9S by spectroscopic and chemical methods. All the described products are formally derived by unprecedented enzymatic oxidation of C16 fatty acids. Conversion of hexadeca-6,9,12-trienoic acid (C16:3 omega-4) into 3 unequivocally established the occurrence of (at least) a specific 9S-oxygenase activity. To the best of our knowledge, the present data reveal for the first time the existence of an organic network of oxygenase-mediated transformations that require C16 fatty acids as substrates in living cells.

Effects of soybean lipoxygenase-1 on phosphatidylcholines containing furan fatty acids

Naturally occurring tetraalkylsubstituted furan fatty acids (F-acids) were tested as potential substrates for soybean lipoxygenase-1. For this purpose, F-acid methyl ester and phosphatidylcholines containing F-acids at the sn-2 position of the glycerol residue were incubated with the enzyme. Oxidation of F-acids only occurs in the presence of linoleic acid as co-substrate. Linoleic acid is converted by lipoxygenase to the corresponding hydroperoxide that oxidizes the F-acid, probably in a radical reaction, to form an unstable dioxoene compound. This intermediate then forms, dependent on pH, unsaturated furanoid acids or isomers with cyclopentenolone structure that can be detected by gas chromatography/mass spectrometry (GC/MS). F-acids located at the sn-2 position of a synthetic phosphatidylcholine (PC), containing linoleic acid in the sn-1 position, are co-oxidized to a greater extent by incubation with soybean lipoxygenase-1 than are F-acids bound to PC with myristic acid in the sn-1 position when subjected to the enzyme in the presence of a great excess of linoleic acid. The results suggest that F-acids may play a strategic role in antioxidative processes in plant cells.

Bile acids: antioxidants or enhancers of peroxidation depending on lipid concentration

Using three different assay systems, we have discovered a heretofore unrecognized antioxidant property of bile acids at physiological concentrations. Bile acids inhibit peroxidation of the polyunsaturated lipid, linoleic acid, and of the highly fluorescent protein phycoerythrin. In part, the antioxidant activity results from scavenging of peroxyl radicals by direct oxidation of the bile acids. The most abundant products of the reaction of cholate and chenodeoxycholate with peroxyl radicals were studied in detail and shown to be the keto derivatives formed by oxidation of the 7 alpha-hydroxyl groups. Paradoxically, at linoleate concentrations higher than 1-2 mM, glycocholate up to approximately 10-14 mM enhances lipid peroxidation and inhibits only at higher concentrations. These findings may prove important in understanding the etiology of certain disease states of the biliary tract and intestine where lipid peroxidation may be involved and in providing a rationale for the positive epidemiological correlation between high lipid intake and higher fecal bile acid output and colon cancer.

Resolution of the isoenzymes of soybean lipoxygenase using isoelectric focusing and chromatofocusing

Isoelectric focusing in thin-layer polyacrylamide gels has been applied to the analysis of the enzymes involved in the formation and destruction of peroxides in soybeans [Glycine max (L.)], lipoxygenases and peroxidases, respectively. As a result of differences in pH optima for catalytic activity, lipoxygenases were selectively detected by adjusting the pH employed for activity-specific staining. Type-1 lipoxygenase was revealed not only by staining based on the conversion of linoleic acid to hydroperoxide but also by two stains based on the reduction of the hydroperoxide. These methods were found to be suitable for the analysis and characterization of isoenzyme patterns in different soybean cultivars. A substantial difference in the distribution of lipoxygenases maximally active near pH 7 was observed for cultivars Provar and Vickery. A similar degree of separation of the isoenzymes was achieved on a larger scale using chromato-focusing in the pH range 7.4-5.0.

Legume lipids

The storage lipids of legume seeds are a major source of dietary fat. As a result of their importance in the food industry, much is known about lipid composition, chemistry, flavor, off-flavor development, and their technological implications in foods of dry, oil-rich seeds such as soybeans and peanuts. Lipids from green pea have also been investigated to some extent. Other food legume lipids have not been studied in any great detail because of their low lipid content and limited or negligible use for oil purposes. Literature on the biochemical, nutritional, and toxicological aspects of lipids from these other legumes is scanty, compared to published reports of seed lipids from soybean and peanuts. Lipids of soybean, peanut, and green pea are reported in this article. Their chemistry, interactions with other constituents, role in flavor development, as well as alterations due to processing and removal of off-flavors are reviewed. The nutritional and toxicological implications of legume lipids from soybean, peanuts, and other food legumes are also discussed.

A study of oxygen isotope scrambling in the enzymic and non-enzymic oxidation of linoleic acid

Lipoxygenases-1 and -2 isolated from soybeans were incubated with linoleic acid in the presence of a mixture of 16O2 and 18O2. The formation of 16O/18O-molecules which is indicative for a head-to head reaction of peroxy radicals was determined and compared with that produced during autoxidation of a linoleic acid emulsion in the presence of ferric ions. Lipoxygenase-1 was much less active in scrambling than lipoxygenase-2 which was comparable to that found in the autoxidation reaction.

Oxidation of 3-oxygenated delta 4 and delta 5 - C27 steroids by soybean lipoxygenase and rat liver microsomes

The formation of dioxygenated metabolites of cholesterol, epicholesterol (5-cholesten-3 alpha-ol) 4-cholesten-3 beta-ol, 4-cholesten-3 alpha-one and 4-stigmasten-3-one was studied after incubations with soybean lipoxygenase and linoleic acid. From cholesterol and epicholesterol were formed the 7 alpha-hydroxy, 7 beta-hydroxy-, 7 beta-hydroperoxy-, 7-oxo and 5,6-epoxy-derivatives as well as 6 beta-hydroxy-4-cholesten-3-one. All delta 4-steroids were hydroxylated in the 6 alpha- and 6 beta-positions. The ratios between the yields of 6 beta- and 6 alpha-hydroxylated metabolites varied between 3:1 and 2:1. Incubations with 4-cholesten-3 alpha-ol and 4-cholesten-3 beta-ol also afforded the 4,5-epoxides of these steroids. The ratios between the yields of the 4 beta, 5 beta- and 4 alpha, 5 alpha-epoxides were ca. 4:1 for 4-cholesten 3 beta-ol and ca. 3:2 for 4-cholesten-3 alpha-ol. With iron-supplemented microsomes from rat liver, the compounds formed were qualitatively and quantitatively the same as with soybean lipoxygenase, whereas with 18,000 X g rat liver supernatant fractions the yields of all products formed--except 7 alpha-hydroxycholesterol and 6 beta-hydroxy-4-cholesten-3-one--were markedly decreased. The results indicate the presence of a rat liver microsomal 6 beta-hydroxylase which can use 4-cholesten-3-one as a substrate and extend previous findings of similarities between soybean lipoxygenase and a nonspecific lipoxygenase in rat liver microsomes.

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.

1H NMR study of the conversion of 13(S)-hydroperoxy linoleic acid by soya bean lipoxygenase I

The conversion of 13(S)-hydroperoxy linoleic acid by lipoxygenase I at 298 K was monitored by 1H NMR and ultraviolet absorption spectroscopy. The rate constant for the conversion of the hydroperoxide, k = 45.8 +/- 7.5 M-1 . s-1, depends on the concentrations of both enzyme and hydroperoxide. This constant is not affected by O2, nor by solvent isotope effects.

Cyclic peroxides from a soya lipoxygenase-catalysed oxygenation of methyl linolenate

Incubation of methyl linolenate with an aqueous extract of soyabean flour at neutral pH gives the hydroperoxyendoperoxides 16-hydroxyperoxy-13,15-endoperoxylinolenate and 9-hydroxyperoxy-10,12-endoperoxylinolenate as the principal oxygenation products in addition to monohydroperoxides. Lipoxygenase I (EC 1.13.11.12) does not catalyse the oxygenation under this condition. The enzyme contributing most to the formation of the hydroperoxyendoperoxides is assumed to be a high molecular mass lipoxygenase aggregate.

Purification and characterization of two isoenzymes of lipoxygenase from soybeans

A chromatographic procedure for the purification of two lipoxygenase isoenzymes (linoleate: O2 oxidoreductase, EC 1.13.11.12.) from soybean is described. The procedure for the purification of isoenzyme L-1 includes optimalized extraction, ammonium sulfate fractionation, heat treatment and gradient elution from a CM-Sephadex C-50 column. The purification of L-2 includes ammonium sulfate fractionation, gelfiltration on Sephadex G-150 and gradient elution from a DEAE-cellulose column. Both isoenzymes L-1 and L-2 appear homogeneous after Disc-PAGE. The isoelectric points are 5.6 for L-1 and 5.8 for L-2. Molecular weights are estimated as 100,000 for L-1 as well as L-2 applying three different methods. Both isoenzymes contain 0.9 mol iron per mol protien. The estimated turn over numbers are 8,200 mol linoleate per mol enzyme and min for L-1 and 3,100 for L-2. Amino acid compositions determined after acid hydrolysis show marked differences between L-1 and L-2, particularly with respect to the amino acids Lys, Phe, Ser, Gly and Leu. L-1 posesses a total of 9 cysteine molecules, 6 of which are present as disulfide bonds. L-2 posesses a total of 8 cysteine molecules with only one disulfide bond.

[Co-oxydation of linoleic acid to volatile compounds by lipoxygenase isoenzymes from soya beans (author's transl)]

Lipoxygenase isoenzymes L-1 (optimum pH 9.0) and L-2 (pH 6.5) were incubated with linoleic acid. The extracted volatile compounds were separated by gas-chromatography and analysed by mass spectrometry. The relative amounts of volatile carbonyl compounds, which were formed during catalysis were determined (mole percent). L-1 yielded hexanal (greater than 90% at pH 7 and 70% at pH 8.5). L-2 at pH 7 yielded hexanal (31), two geometric isomers of 2,4-decadienal (40), 2-trans-heptenal (12) and 2-trans-octenal (10).

[Co-oxidation of beta-carotene and canthaxanthine by purified lipoxygenases from soya beans (author's transl)]

Isolation and purification of soya bean lipoxygenase (linoleate: O2 oxidoreductase, EC, 1.13.11.12) on Sephadex G-200, DEAE-cellulose and by isolectric focusing yields two isoenzymes of the L- 2 type (optimum pH 6.5) and two of the L-1 type (optimum pH9.0). Different crude extracts from soya beans as well as the purified L-2 isoenzymes exhibit the same capacity for co-oxidation of beta-carotene and canthaxanthine, when the comparison is based upon equal lipoxygenase activities. In contrast to L-2 the alkaline lipoxygenase L-1 is a poor "carotene oxidase".

Biochemistry of lipoxygenase in relation to food quality

A renewed interest in lipoxygenase has led to detailed studies of its isoenzymes, substrate specificity, and the nature of its reaction products. Lipoxygenase is highly specific for cis,cis-1,4-pentadiene systems such as linoleic, linolenic, and arachidonic acid (or ester) and catalyzes the formation of the corresponding hydroperoxides with a cis,-trans-conjugated diene system. The hydroperoxides can then undergo enzymic or spontaneous degradation, producing a range of carbonyl compounds. This review will discuss the biochemical properties of this enzyme and its contribution to the quality of raw and processed food products. An attempt has been made to discuss both the desirable and undesirable effects associated with the action of lipoxygenase, citing specific food examples where appropriate.

Affinity chromatography of lipoxygenases

A number of aminohexyl agarose derivatives of unsaturated fatty acids have been prepared and evaluated as materials for the affinity chromatography of soybean and pea lipoxygenases. A practical method for a one-stage purification of soybean lipoxygenase-1, with a purification factor of 16, is described, using either linolenate or docosa-4,7,10,13,16,19-hexaenoate as ligands. Results show that alleged competitive inhibitors do not cause sharp elution from the affinity column, and that there is an increasing specificity of binding and sharpness of elution as the proportion of unsaturation in the ligand is increased. These results are discussed in terms of the relative importance of the types of bonding involved in enzyme-substrate binding.

Steady-state kinetics of lipoxygenase oxygenation of unsaturated fatty acids

The oxygenation of linoleate and arachidonate catalyzed by soybean lipoxygenase is subject to competitive product inhibition. For normal conditions, there is an additional inhibition due to product that causes the reaction to cease before completion. This process is reversible upon addition of further substrate and is proposed to be a chemical (reversible) change of the enzyme. At very low enzyme concentrations, inactivation or adsorption of enzyme on the vessel surface (or "wall effect") is significant, leading to even lower rates and percent completions. In the very early stages of a typical catalyzed reaction, a lag, or induction period, occurs. It was previously known that this lag is eliminated by product hydroperoxide--and not by the corresponding alcohol. The hydroperoxide elimination of the lag is inhibited by the alcohol. It is proposed that this is a chemical activation of the enzyme to produce a catalytically functional form.

Preparation and purification of lipid hydroperoxides from arachidonic and gamma-linolenic acids

Commercial soybean lipoxygenase may be used under carefully controlled reaction conditions to give high yields of lipid hydroperoxides. Lipid hydroperoxides so derived from gamma-linolenic or arachidonic acid may be purified by high pressure liquid chromatography. Thus, commercial lipoxygenase serves as a viable source for 100 mg quantities of lipid hydroperoxides.

Co-oxydation of a carotenoid by the enzyme lipoxygenase: influence on the formation of linoleic acid hydroperoxides

A partially purified soybean lipoxygenase (L-3) was incubated for 15 min at pH 6.5 with linoleic acid and oxygen. Systems with and without the polyene glycoside crocin were compared. The system with crocin reacted with higher velocity with oxygen than did the control experiment without polyene. From the crocin 40% was destroyed. In the presence of crocin about 40% more linoleic acid hydroperoxides was formed than without the polyene but the linoleic acid break-down was equal in both experiments. L-3 peroxidises linoleic acid to 13L:13D:9L:9D-hydroperoxides in the proportions 43:11:21:25. In the presence of crocin the ratio of the isomers changed to 64:11:11:14.