Lipoxygenase biocatalysis: a survey of asymmetric oxygenation

Synthesis of Linoleic Acid 13-Hydroperoxides from Safflower Oil Utilizing Lipoxygenase in a Coupled Enzyme System with In-Situ Oxygen Generation

Linoleic acid hydroperoxides are versatile intermediates for the production of green note aroma compounds and bifunctional ω-oxo-acids. An enzyme cascade consisting of lipoxygenase, lipase and catalase was developed for one-pot synthesis of 13-hydroperoxyoctadecadienoic acid starting from safflower oil. Reaction conditions were optimized for hydroperoxidation using lipoxygenase 1 from Glycine max (LOX-1) in a solvent-free system. The addition of green surfactant Triton CG-110 improved the reaction more than two-fold and yields of >50% were obtained at linoleic acid concentrations up to 100 mM. To combine hydroperoxidation and oil hydrolysis, 12 lipases were screened for safflower oil hydrolysis under the reaction conditions optimized for LOX-1. Lipases from Candida rugosa and Pseudomonas fluorescens were able to hydrolyze safflower oil to >75% within 5 h at a pH of 8.0. In contrast to C. rugosa lipase, the enzyme from P. fluorescens did not exhibit a lag phase. Combination of P. fluorescens lipase and LOX-1 worked well upon LOX-1 dosage and a synergistic effect was observed leading to >80% of hydroperoxides. Catalase from Micrococcus lysodeikticus was used for in-situ oxygen production with continuous H2O2 dosage in the LOX-1/lipase reaction system. Foam generation was significantly reduced in the 3-enzyme cascade in comparison to the aerated reaction system. Safflower oil concentration was increased up to 300 mM linoleic acid equivalent and 13-hydroperoxides could be produced in a yield of 70 g/L and a regioselectivity of 90% within 7 h.

Catalytic characterization of heterodimeric linoleate 13S-lipoxygenase from black soybean (Glycine max (L.) Merr.)

A novel lipoxygenase (BLOX) was purified from black soybean (Glycine max (L.) Merr.), and its catalytic properties were characterized. The molecular weight of BLOX was 101 kDa and its unique heterodimeric structure with two different subunits of molecular weight 46 kDa and 55 kDa was elucidated. The optimum pH and temperature of BLOX were pH 9.5 and 40 °C, respectively. BLOX was highly stable at the pH range of 6.0-10.0 and below 40 °C, and was stimulated by adding ferrous ion (Fe2+). In terms of substrate specificity, BLOX showed a substrate preference to linoleic acid that is the main substance to produce hydroperoxides in soybean. When it reacted with linoleic acid, the major product was 13(S)-hydroperoxy-9,11-octadecadienoic acid; therefore, it could be classified into the linoleate 13S-LOX family (EC 1.13.11.12). Finally, the kinetic parameters (Vmax, Km, and kcat) of BLOX were 0.124 mM min-1, 0.636 mM, and 12.28 s-1, respectively, and consequently, the catalytic efficiency (kcat/Km) was calculated as 1.93 × 104 M-1·s-1. These catalytic characteristics of BLOX could contribute to understanding the enzymatic rancidification of black soybean, and to further biotechnical approaches to control and mitigate the deterioration.

Photobiocatalytic synthesis of chiral secondary fatty alcohols from renewable unsaturated fatty acids

En route to a bio-based chemical industry, the conversion of fatty acids into building blocks is of particular interest. Enzymatic routes, occurring under mild conditions and excelling by intrinsic selectivity, are particularly attractive. Here we report photoenzymatic cascade reactions to transform unsaturated fatty acids into enantiomerically pure secondary fatty alcohols. In a first step the C=C-double bond is stereoselectively hydrated using oleate hydratases from Lactobacillus reuteri or Stenotrophomonas maltophilia. Also, dihydroxylation mediated by the 5,8-diol synthase from Aspergillus nidulans is demonstrated. The second step comprises decarboxylation of the intermediate hydroxy acids by the photoactivated decarboxylase from Chlorella variabilis NC64A. A broad range of (poly)unsaturated fatty acids can be transformed into enantiomerically pure fatty alcohols in a simple one-pot approach.

Natural fatty acids are important starting materials in bio-based chemical production. Here, the authors developed a two-enzyme cascade to produce enantiomerically pure secondary fatty alcohols from natural unsaturated fatty acids in one pot.

Lyophilized extracts from vegetable flours as valuable alternatives to purified oxygenases for the synthesis of oxylipins

In this work, the whole aqueous extracts of soybean flour and oat flour have been used as valuable alternatives to purified oxygenase enzymes for the preparation of oxylipins derived from (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoic acid (EPA). The lipoxygenase activity in the aqueous extracts of soybean (Glycine max. L.) flour was monitored with linoleic acid as substrate and compared with the commercially available purified enzyme (LOX-1). Oat flour extracts (Avena sativa L.) were evaluated for their peroxygenase activity by comparing different enzyme preparations in the epoxidation of methyl oleate. It was found that lyophilization of the aqueous extracts from these vegetable flours offers advantages in terms of enzyme stability, reproducibility and applicability to preparative organic synthesis. The lyophilized enzyme preparations were tested for the oxyfunctionalization of EPA and the formed products were isolated in satisfactory yields. In the presence of lyophilized extract from soybean, EPA gave 15S-hydroxy-(5Z,8Z,11Z,13E,17Z)-eicosapentaenoic acid in enantiopure form as exclusive product. Peroxygenase from oat flour was less selective and catalyzed the formation of different epoxides of EPA. However, the biocatalyzed epoxidation of EPA under controlled conditions allowed to obtain optically active (17R,18S)-epoxy-(5Z,8Z,11Z,14Z)-eicosatetraenoic acid (65% ee) as the main monoepoxide, among the five possible ones.

Biocatalytic Synthesis of Natural Green Leaf Volatiles Using the Lipoxygenase Metabolic Pathway

In higher plants, the lipoxygenase enzymatic pathway combined actions of several enzymes to convert lipid substrates into signaling and defense molecules called phytooxylipins including short chain volatile aldehydes, alcohols, and esters, known as green leaf volatiles (GLVs). GLVs are synthesized from C18:2 and C18:3 fatty acids that are oxygenated by lipoxygenase (LOX) to form corresponding hydroperoxides, then the action of hydroperoxide lyase (HPL) produces C6 or C9 aldehydes that can undergo isomerization, dehydrogenation, and esterification. GLVs are commonly used as flavors to confer a fresh green odor of vegetable to perfumes, cosmetics, and food products. Given the increasing demand in these natural flavors, biocatalytic processes using the LOX pathway reactions constitute an interesting application. Vegetable oils, chosen for their lipid profile are converted in natural GLVs with high added value. This review describes the enzymatic reactions of GLVs biosynthesis in the plant, as well as the structural and functional properties of the enzymes involved. The various stages of the biocatalytic production processes are approached from the lipid substrate to the corresponding aldehyde or alcoholic aromas, as well as the biotechnological improvements to enhance the production potential of the enzymatic catalysts.

High-Speed Counter-Current Chromatography (HSCCC) Purification of Antifungal Hydroxy Unsaturated Fatty Acids from Plant-Seed Oil and Lactobacillus Cultures

Hydroxy unsaturated fatty acids (HUFA) can function as antifungal agents. To investigate the antifungal spectrum, that is, the scope of the in vitro fungal-inhibition activities of HUFA and their potential applications, three HUFA were produced by microbial transformation or extracted from plant-seed oils; these compounds included coriolic acid (13-hydroxy-9,11-octadecadienoic acid) from Coriaria seed oil, 10-hydroxy-12-octadecenoic acid from cultures of Lactobacillus hammesii, and 13-hydroxy-9-octadecenoic acid from cultures of Lactobacillus plantarum TMW1.460Δlah. HUFA were purified by high-speed counter-current chromatography (HSCCC), characterized by LC-MS and MS/MS, and their antifungal activities were evaluated with 15 indicator fungal strains. The HUFA had different antifungal spectra when compared with unsaturated fatty acids with comparable structures but without hydroxy groups. The inhibitory effects of HUFA specifically targeted filamentous fungi, including Aspergillus niger and Penicillium roqueforti, whereas yeasts, including Candida spp. and Saccharomyces spp., were resistant to HUFA. The findings here support the development of food applications for antifungal HUFA.

Photobiocatalytic decarboxylation for olefin synthesis

The oxidative decarboxylation of fatty acids to terminal alkenes was accomplished with high selectivity by combining a fatty acid decarboxylase OleT_JE with the light-catalyzed generation of the cosubstrate hydrogen peroxide, resulting in a simple and efficient system for the light-driven cleavage of C–C bonds.

Cationic substrates of soybean lipoxygenase-1

Soybean lipoxygenase-1 (SBLO-1) catalyzes the oxygenation of 1,4-dienes to produce conjugated diene hydroperoxides. The best substrates are anions of fatty acids; for example, linoleate is converted to 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate. The manner in which SBLO-1 binds substrates is uncertain. In the present work, it was found that SBLO-1 will oxygenate linoleyltrimethylammonium ion (LTMA) to give primarily13(S)-hydroperoxy-9(Z),11(E)-octadecadienyltrimethylammonium ion. The rate of this process is about the same at pH 7 and pH 9 and is about 30% of the rate observed with linoleate at pH 9. At pH 7, SBLO-1 oxygenates linoleyldimethylamine (LDMA) to give primarily 13(S)-hydroperoxy-9(Z),11(E)-octadecadienyldimethylamine. The oxygenation of LDMA occurs at about the same rate as LTMA at pH 7, but more slowly at pH 9. The results demonstrate that SBLO-1 will readily oxygenate substrates in which the carboxylate of linoleate is replaced with a cationic group, and the products of these reactions have the same stereo- and regiochemistry as the products obtained from fatty acid substrates.

Inhibitory effect on soybean lipoxygenase and docking studies of some secondary metabolites, isolated from Origanum vulgare L. ssp. hirtum

In this study, five secondary metabolites (caffeic acid, rosmarinic acid, lithospermic acid B, 12-hydroxyjasmonic acid 12-O-beta-glucoside and p-menth-3-ene-1,2-diol 1-O-beta-glucopyranoside) isolated from the polar extracts of the plant Origanum vulgare L. ssp. hirtum, were tested in vitro for their ability to inhibit soybean lipoxygenase. Among the examined compounds, lithospermic acid B demonstrated the best inhibitory activity on soybean lipoxygenase with IC50 = 0.1 mM. Docking studies have been undertaken as an attempt for better understanding the interactions of these compounds within the active site of soybean lipoxygenase. The predicted binding energy values correlated well with the observed biological data.

Purification, product characterization and kinetic properties of lipoxygenase from olive fruit (Olea europaea L.)

Lipoxygenase from olive fruit was purified to homogeneity for the first time after differential centrifugations and by hydrophobic chromatography. The enzyme had a molecular mass of 98 kDa and exhibited a maximal activity at pH 6. Lipoxygenase had a better affinity for linoleic acid (Km=82.44 microM) than for linolenic acid (Km = 306.26 microM). It is inhibited by linoleate:oxygen oxidoreductase (LOX) inhibitors like nordihydroguaiaretic acid (NDGA) or propyl gallate. The reaction product was 13-hydroperoxy octadecadienoic acid when linoleic acid was used as substrate.

Lipoxygenases: occurrence, functions and catalysis

Lipid peroxidation is common to all biological systems, both appearing in developmentally and environmentally regulated processes. Products are hydroperoxy polyunsaturated fatty acids and metabolites derived there from collectively named oxylipins. They may either originate from chemical oxidation or are synthesized by the action of various enzymes, such as lipoxygenases (LOXes). Signalling compounds such as jasmonates, antimicrobial and antifungal compounds such as leaf aldehydes or divinyl ethers, and a plant-specific blend of volatiles including leaf alcohols are among the numerous products. Cloning of many LOXes and other key enzymes metabolizing oxylipins, as well as analyses by reverse genetic approaches and metabolic profiling revealed new insights on oxylipin functions, new reactions and the first hints on enzyme mechanisms. These aspects are reviewed with respect to function of specific LOX forms and on the development of new models on their substrate and product specificity.