Purification of soybean lipoxygenase by affinity chromatography

Enhanced production of hydroperoxides by immobilized lipoxygenase in the presence of cyclodextrins

The advantages of the presence of cyclodextrins in a reaction catalyzed by immobilized lipoxygenase at neutral pH are reported for the first time. The steady-state rate in the presence of beta-cyclodextrins was seven times higher than in control experiments using the same concentration of linoleic acid; furthermore the percentage of substrate conversion (and product accumulation) obtained in the presence of beta-cyclodextrins was higher than in the control assays. The optimum concentration of free linoleic acid coincided with the critical micellar concentration for linoleic acid at neutral pH. The operational stability of the immobilized enzyme increased in the presence of beta-cyclodextins, while an increase in the percentage of 13-HPOD was also observed.

The interaction between beta-carotene and lipoxygenase in plant and animal systems

The effect of beta-carotene (BC) on the activity of lipoxygenase (LOX) from plant and animal sources has been examined. Soybean lipoxygenase L-2 activity towards linoleate was inhibited by BC by a maximum of 70% at pH 6.5, whereas L-1 activity was little affected at pH 9.0. Lineweaver-Burk plots indicated that BC inhibited LOX activity by mixed competitive/non-competitive mechanisms. Other hydrophobic compounds also inhibited LOX activity; oleic acid and retinol were competitive inhibitors whereas tocopherol acetate and 5,8,11,14-eicosatetraynoic acid (ETYA) were non-competitive inhibitors. Binding studies with L-2 LOX bound to Sepharose indicated BC-binding and inhibition with the immobilized LOX. Activity of LOX from animal sources was also inhibited by BC both towards linoleate and arachidonate.

Lipoxygenase and other enzymes of arachidonic acid metabolism in the brain of chicks affected by nutritional encephalomalacia

1. Prostaglandin endoperoxide synthetase (PES) and lipoxygenase (Lox) activities were compared in the cerebella and cerebra of vitamin E-sufficient young chicks and in chicks in which nutritional encephalomalacia (NE) was induced by a diet deficient in vitamin E. 2. Eicosanoid production patterns were qualitatively similar in the brains of both groups of chicks, but prostaglandin production was 50-60% less in cerebella of ataxic chicks, compared to control cerebella, while the opposite trend was observed in the cerebellar Lox pathway, as measured by radioimmunoassay of 15-HETE. 3. Cerebellar phospholipase A2 activity was twice that of the cerebrum but was not affected by NE. 4. Purification of Lox activity from the cerebellar homogenates produced a lower yield and enrichment when the starting material was taken from ataxic chicks, compared to the controls. 5. In addition there were qualitative differences in the purified fractions from both groups, as seen by pH optima and kinetics. 6. The results are consistent with the view that the cerebellum has less antioxidant protection than the cerebrum and that its higher phospholipase A2 activity and greater propensity to oxygenate arachidonic acid via the Lox pathway at the expense of the PES pathway may render this region of the brain particularly vulnerable to oxidative damage in NE.

Lipoxygenase activity in the brain regions of young chicks: isolation and some properties

1. The lipoxygenase (LOX) oxygenation pathway of arachidonic acid was investigated in the cerebellum and cerebral hemispheres of young chicks. 2. Lipoxygenase products consisted mainly of 15-hydroxyeicosatetraenoic acid (15-HETE), accompanied by the 15-hydroperoxy analog (15-HPETE) and the 5-HETE product. 3. The yield of 15-HETE was 3 times greater in the cerebellar system than in the cerebrum. 4. PLA2 activity of the cerebellum was twice that of the cerebrum. 5. Affinity chromatography revealed 2 brain fractions with LOX activity which were assayed with either linoleic or arachidonic acid as substrate. 6. The fraction eluted with 0.2 M sodium acetate pH 5.0, produced a higher yield and enrichment of LOX activity than the eluate obtained with 0.1 M Tris-HCl buffer (pH 8.0). 7. A considerably higher yield and enrichment of the enzyme was achieved when the starting material was the cerebellum, compared to the cerebrum. 8. The optimal pH for both purified fractions from cerebrum and cerebellum was 6.5, with either linoleic or arachidonic acid as substrate. 9. The cerebral LOX yielded Michaelis-Menten kinetics when linoleic acid was the substrate, while the corresponding plots for the cerebellar enzyme were sigmoidal. 10. Arachidonic acid as substrate produced sigmoidal plots, except at pH 5.0, where Michaelis-Menten kinetics were observed. 11. These results and the elevated activities of PLA2 and 15-LOX could be significant in relation to the special vulnerability of the cerebellum in chick nutritional encephalomalacia.

Inhibition of soybean lipoxygenase-1 by n-alcohols and n-alkylthiols

A series of n-alcohols and n-alkylthiols with carbon chains from 2 to 12 were examined for the inhibition of soybean lipoxygenase-1 (L-1). The alcohol produces a competitive inhibition, the extent of which increases with an increase in the carbon number of alkyl chain up to 8. Whereas the inhibition of the alkylthiol is noncompetitive, the extent of which is almost independent from the carbon number. From the behavior of pKi dependence on the carbon number of the alcohol, the decyl group appears to be optimum to bind to L-1. The thermodynamic analysis for the inhibition based upon van 't Hoff equation indicates positive enthalpy and entropy changes for the binding of the alcohol to the enzyme and negative enthalpy and positive to negative entropy changes for that of the alkylthiol. These observations suggest that the alcohol inhibits L-1 by binding of the hydrophobic alkyl tail to the catalytic site of the enzyme by a hydrophobic interaction. The alkylthiol inhibits by binding of the nucleophilic sulfhydryl head to a polarizable region of the enzyme and the alkyl tail to a hydrophobic region of the enzyme free from the steric hindrance as an anchor.

Biochemical studies on a 12-lipoxygenase in human uterine cervix

Human uterine cervix possesses a high 12-lipoxygenase activity; this enzyme has been isolated in a purified form from the squamous epithelial region of human cervix and its major properties have been investigated. Enzyme activity was present in all subcellular fractions obtained by centrifugation; the highest specific activity was associated with the microsome fraction (160,000 X g pellet). Purification of the enzyme was achieved by acetone precipitation, ion exchange chromatography on CM-cellulose and affinity chromatography on linoleyl-aminoethyl-Sepharose. The product from the incubation of sodium [1-14C]arachidonate with crude enzyme extracts co-chromatographed with authentic 12-hydroxyeicosatetraenoic acid, but the purified enzyme gave a product that behaved like the 12-hydroperoxy derivative. The enzyme had optimum activity at pH 6.5, a Km of 15 microM for arachidonic acid and was stimulated by ATP and Ca2+. Enzyme activity was inhibited by esculetin, nordihydroguaiaretic acid, eicosatetraynoic acid, detergents at concentrations greater than 0.1% (w/v) and preincubation of substrate with GSH and GSH peroxidase. The occurrence of a high 12-lipoxygenase activity is discussed in relation to the specific physiological functions of this tissue.

New aspects of the inhibition of soybean lipoxygenase by alpha-tocopherol. Evidence for the existence of a specific complex

The formation of alpha-tocopherol--lipoxygenase complex was elucidated using immobilized affinity purified soybean lipoxygenase and [D-3H]alpha-tocopherol. The alpha-tocopherol--lipoxygenase complex did not dissociate on addition of linoleic acid. Iodoacetate modified immobilized lipoxygenase did not form the complex with alpha-tocopherol. Lipoxygenase attached to an aminoethyl linoleyl Sepharose column was eluted by alpha-tocopherol. DL-alpha-Tocopherol acetate at a concentration of 3 X 10(-3) M inhibited 80% of linoleate oxidation by soybean lipoxygenase. The lipoxygenase--alpha-tocopherol complex did not give the usual soybean lipoxygenase antigenic pattern in immunodiffusion. Digestion of the [3H]alpha-tocopherol--lipoxygenase complex with proteolytic enzymes showed that most of the radioactivity is incorporated into one peptide.

Lipoxygenase from baker's yeast: purification and properties

Lipoxygenase activity was extracted from the mitochondrial fraction of baker's yeast and was purified by affinity chromatography on a linoleyl aminoethyl sepharose column. Two lipoxygenases were eluted from the affinity column. The second enzyme eluted was characterized as a true lipoxygenase. The lipoxygenase eluted showed maximum activity at pH 6.5 with a Km of 2.68 X 10(-4) M on linoleate. The reaction products of the second lipoxygenase with linoleate were characterized by u.v., i.r., NMR spectra and mass spectrometry and were found to be: 9-hydroperoxy-octadeca-trans-10,cis-12-dienoic acid and 13-hydroperoxy-octadeca-cis-9,trans-11-dienoic acid.

Lipoxygenase-like enzyme in rat testis microsomes

Microsomes, separated from rat testes, were found capable of oxidizing linoleate and arachidonate. The enzyme activity was solubilized with 1% Triton X-100 in acetate buffer (pH 5.0) and purified by affinity chromatography. The overall purification from the starting preparation was approx. 40-fold. The affinity-purified enzyme was almost homogeneous as determined by electrophoresis in polyacrylamide gel. The enzyme was characterized as lipoxygenase-like from its spectrum, specificity, effect of linoleate on its fluorescence and linoleate oxidation products. Three types of compounds separated by thin-layer chromatography were generally present in the lipoxygenase-like enzyme reaction on linoleic acid: substrate fatty acid, polar by-products and hydroperoxides. The hydroperoxides were analyzed by infrared spectra and mass spectrometry and showed the presence of both 9- and 13-hydroxy isomers.

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.