Comparative activity of natural mono-, di- and tri-hydroxy derivatives of arachidonic acid on guinea-pig lungs: myotropic effect and stimulation of cyclooxygenase activity

The activity of natural 5,6-Dihydroxy-eicosatetraenoic acid (5,6-DiHETE; 2 isomers), 5S,15S-DiHETE, 8S,15S-DiHETE, 5S,12S-DiHETE, delta 6-trans-leukotriene B4, 12-epi-delta 6-trans-leukotriene B4, omega-hydroxy-leukotriene B4, omega-carboxy-leukotriene B4, 15S-hydroxyeicosatetraenoic acid (15S-HETE), 12S-HETE, 5S-HETE and 12S-hydroxy-heptadecatrienoic acid was compared to LTB4 on the guinea-pig lung parenchymal strip and on the release of prostaglandins and thromboxanes by the perfused guinea-pig lungs. The omega-hydroxy-LTB4 appeared more potent than LTB4 both for inducing a contraction and for releasing prostanoids whereas the omega-carboxy-LTB4 was much less active on the parenchyma and did not release prostanoids at the dose used. All other hydroxy acids tested were either very weakly active or inactive in the two systems used with the exception of the 5,6-DiHETEs which showed significant activity. These di-hydroxy acids induced contractions of the lung parenchymal strip which could be blocked by FPL-55712 but were inactive on the guinea-pig ileum. The 5S-HETE, 12S-HETE and 15S-HETE were also tested for possible myotropic activity on selected smooth muscle preparations. Our results provide further informations on the structural requirements for LTB4 (and other hydroxy acids) actions on the guinea-pig lungs.     

5-aminosalicylic acid inhibits leukotriene B4ω-hydroxylase activity in human polymorphonuclear leukocytes

ω-oxidation is regarded as the major pathway for the metabolism and inactivation of leukotriene B₄ (LTB₄). To investigate the action of 5-aminosalicylic acid (5-ASA) on LTB₄ω-hydroxylase activity, we incubated human polymorphonuclear leukocytes (PMNLs) with ³H-labeled LTB₄ after pre-incubation with various concentrations of 5-ASA. ω-oxidation metabolites were separated by high performance liquid chromatography and each radioactivity was measured by a liquid scintilation counter. LTB₄ω-hydroxylase activity was inhibited by 5-ASA in a concentration-dependent fashion. The 50% inhibitory dose was about 50 μmol/l, which is within the concentration range found in the colonic mucosa. Our findings may be valuable in elucidating the potentially critical aspect of 5-ASA treatment in ulcerative colitis (UC).     

Generation of leukotriene B4 and leukotriene E4 from porcine pulmonary artery

When chopped porcine pulmonary arteries were incubated with calcium ionophore A23187 (1) in the presence of indomethacin there was a time dependent generation of a substance which produced contractions of superfused strips of guinea-pig ileum smooth muscle (GPISM) which were indistinguishable from those induced by LTD₄. This material however had a different retention time from LTD₄ when subjected to HPLC and co-chromatographed with synthetic LTE₄. In addition to LTE₄ a substance which had properties indistinguisable from those of LTB₄ when assayed on a combination of guinea-pig lung parenchymal strips (GPP) and GPISM (2) was generated from the pulmonary artery. This substance co-chromatographed with synthetic LTB₄. The adventitia and intima were the richest source of LTE₄, the adventitia releasing slightly more than the intima. The output of LTB₄ and LTE₄ was inhibited by 6,9-deepoxy-6,9-(phenylimino)-Δ^6,8 prostaglandin I₁ (U-60,257). Nordihydroguaiaretic acid (NDGA) inhibited the generation of LTE₄.     

Studies on the mechanism of formation of the 5S,12S-dihydroxy-6,8,10,14(E,Z,E,Z)-icosatetraenoic acid in leukocytes

Incubation of peripheral blood leukocytes with arachidonic acid (and ionophore A23187) led to the formation of leukotriene B₄, Δ⁶-trans-leukotriene B₄, Δ⁶-trans-12-epi-leukotriene B₄, 5-hydroxy-icosatetraenoic acid, 12-hydroxy-icosatetraenoic acid and of 5S,12S-dihydroxy-6,8,10,14-(E,Z,E,Z)-icosatetraenoic acid (5S,12S-DiHETE). Incubation of leukocytes with leukotriene A₄ resulted in the formation of leukotriene B₄ and of its two Δ⁶-trans-isomers but not of the 5S,12S-DiHETE. ¹⁸O₂ labeling experiments have shown that the hydroxyl groups at C5 and C12 in the 5S,12S-DiHETE are derived from molecular oxygen. The tetraacetylenic analog of arachidonic acid was found to be a potent inhibitor of the formation of the 5S,12S-DiHETE whereas it potentiated the synthesis of the 5-hydroxy acid and of leukotriene B₄. Addition of the 12-hydroxy-icosatetraenoic acid to leukocytes, or of the 5-hydroxy-icosatetraenoic acid to a suspension of platelets caused the formation of the 5S,12S-DiHETE. It is concluded that the 5S,12S-DiHETE is not derived from leukotriene A₄ but is a product of the successive reactions of arachidonic acid with two lipoxygenases of different positional specificities.     

Specificity of receptors for leukotrienes A4, B4, C4, D4, E4 and histamine on the guinea-pig lung parenchyma. Effect of FPL-55712 and desensitization of the myotropic activity

The novel metabolites of arachidonic acid, leukotriene (LT) A₄, B₄, C₄, D₄ and E₄ have potent myotropic activity on guinea-pig lung parenchymal strip . The receptors responsible for their action were characterized using desensitization experiments and the selective SRS-A antagonist, FPL-55712. During the continuous infusion of LTB₄, the tissues became desensitized to LTB₄ but were still responsive to histamine, LTA₄, LTC₄, LTD₄ and LTE₄. When LTD₄ was infused continuously, the lung strips contracted to LTB₄ and histamine but were no longer responsive to LTA₄, LTC₄, LTD₄ and LTE₄. Furthermore, FPL-55712 (10 ng ml⁻¹− 10 ug ml⁻¹) produced dose-dependent inhibitions of LTA₄, LTC₄, LTD₄ and LTE₄ without inhibiting the contraction to LTB₄ and histamine. On the basis of these results, it appears that the guinea-pig lung parenchyma may have one type of receptor for LTB₄ and another for LTD₄; LTA₄, LTC₄ and LTE₄ probably act on the LTD₄ receptor.     

The effects of a diet rich in fish oil on human neutrophils: Identification of leukotriene B5 as a metabolite

Diets that are enriched with fish oil have been shown to alter arachidonic acid metabolism via the cyclooxygenase pathway. Recently it has been shown that one of the major component fatty acids of fish oil, eicosapentaenoate (EPA), is a substrate for the leukotriene B (LTB) pathway when added exogenously to human neutrophils . We fed a diet that contained 8–10 gm/day of EPA to four human subjects for three weeks and compared the arachidonate metabolism of their neutrophils to the same functions while the subjects were on their usual diet. The fish oil-supplementation increased neutrophil EPA content from undetectable levels to 7.4 ± 2.4% (p<0.01, expressed as % of total fatty acid), and decreased arachidonate from 15.4 ± 2.3% to 12.8 ± 2.3% (p<0.05). Leukotriene B₅ was identified as a metabolite during the fish oil-diet by its chromatographic profile and mass spectrum. During the experimental diet LTB₄ decreased from 160 ± 37 ng/10⁷ neutrophils to 120 ± 12 (p<0.05), and LTB₅ increased from 0 to 39 ± 9 ng/10⁷ neutrophils (p<0.005). The diet had no effect on neutrophil aggregation or adherence to nylon fibers.     

Leukotriene B4 binding to human neutrophils

[³H] Leukotriene B₄ (LTB₄) binds concentration dependency to intact human polymorophonuclear leukocytes (PMN's). The binding is saturable, reaches equilibrium in 10 min at 4°C, and is readily reversible. Mathematical modeling analysis reveals biphasic binding of [³H] LTB₄ indicating two discrete populations of binding sites. The high affinity binding sites have a dissociation constant of 0.46 × 10⁻⁹M and B_max of 1.96 × 10⁴ sites per neutrophil; the low affinity binding sites have a dissociation constant of 541 × 10⁻⁹M and a B_max of 45.6 × 10⁴ sites per neutrophil. Competitive binding experiments with structural analogues of LTB₄ demonstrate that the interaction between LTB₄ and the binding site is stereospecific, and correlates with the relative biological activity of the analogs. At 25°C[³H] LTB₄ is rapidly dissociated from the binding site and metabolized to 20-OH and 20-COOH-LTB₄. Purification of neutrophils in the presence of 5-lipoxygenase inhibitors significantly increases specific [³H] LTB₄ binding, suggesting that LTB₄ is biosynthesized during the purification procedure. These data suggest that stereospecific binding and metabolism of LTB₄ in neutrophils are tightly coupled processes.     

Corticosteroid suppression of lipoxin A4 and leukotriene B4from alveolar macrophages in severe asthma

Background

An imbalance in the generation of pro-inflammatory leukotrienes, and counter-regulatory lipoxins is present in severe asthma. We measured leukotriene B₄ (LTB₄), and lipoxin A₄ (LXA₄) production by alveolar macrophages (AMs) and studied the impact of corticosteroids.

Methods

AMs obtained by fiberoptic bronchoscopy from 14 non-asthmatics, 12 non-severe and 11 severe asthmatics were stimulated with lipopolysaccharide (LPS,10 μg/ml) with or without dexamethasone (10^-6M). LTB₄ and LXA₄ were measured by enzyme immunoassay.

Results

LXA₄ biosynthesis was decreased from severe asthma AMs compared to non-severe (p < 0.05) and normal subjects (p < 0.001). LXA₄ induced by LPS was highest in normal subjects and lowest in severe asthmatics (p < 0.01). Basal levels of LTB₄ were decreased in severe asthmatics compared to normal subjects (p < 0.05), but not to non-severe asthma. LPS-induced LTB₄ was increased in severe asthma compared to non-severe asthma (p < 0.05). Dexamethasone inhibited LPS-induced LTB₄ and LXA₄, with lesser suppression of LTB₄ in severe asthma patients (p < 0.05). There was a significant correlation between LPS-induced LXA₄ and FEV₁ (% predicted) (r_s = 0.60; p < 0.01).

Conclusions

Decreased LXA₄ and increased LTB₄ generation plus impaired corticosteroid sensitivity of LPS-induced LTB₄ but not of LXA₄ support a role for AMs in establishing a pro-inflammatory balance in severe asthma.     

Production of leukotriene B4 and prostaglandin E2 by turbot (Scophthalmus maximus) leukocytes

Production of two eicosanoids derived from lipoxygenase and cyclooxygenase activities: leukotriene B₄ (LTB₄) and prostaglandin E₂ (PGE₂), respectively, have been simultaneously determined in turbot (Scophthalmus maximus) blood leucocyte and kidney macrophage supernatants by a reverse phase high performance liquid chromatography (HPLC) system coupled with a Diode–Array detector. Levels of LTB₄ after calcium ionophore challenge were 4.08 ng ml⁻¹ in blood leukocyte supernatants and 0.25 ng ml⁻¹ in kidney macrophage supernatants. The levels found for PGE₂ were 428.23 and 606.67 ng ml⁻¹ in blood leukocytes and kidney macrophage supernatants, respectively. When blood leukocytes were treated with the respective inhibitors for the enzymes implicated on the synthesis of both compounds an inhibition of 90.35% was observed for PGE₂ and 76.44% for LTB₄. The detection limit of the method was 0.15 ng ml⁻¹ for LTB₄ and 50 ng ml⁻¹ for PGE₂.     

Structural requirement for the action of leukotriene B4 on the guinea-pig lung:importance of double bond geometry in the 6, 8, 10-triene unit

The action of four synthetic 5(S), 12(R)-dihydroxy-6,8,10,14-eicosatetraenoic acids has been compared to the action of natural leukotriene B₄ (LTB₄) in perfused guinea-pig lung and in the parenchymal strip preparations. Synthetic LTB₄ (Fig. 1) having the 6-$\text{cis}$, 8, 10-$\text{trans}$ triene unit was found to be as powerful as natural LTB₄ both for contracting the parenchymal strip and for releasing prostaglandins and thromboxanes from the perfused lung while three other isomers were inactive. The results indicate that the action of LTB₄ on the lung is highly dependent on the geometry of the conjugated triene.     

Evidence for a dual pathway in platelet activating factor-induced aggregation of rat polymorphonuclear leucocytes

The purpose of this study was to determine the role, if any, of Leukotriene B₄ (LTB₄) in Platelet Activating Factor (PAF)-induced aggregation of rat polymorphonuclear leucocytes (PMNs). Exposure of rat PMNs to 10⁻⁷ M PAF resulted in the release of 4.5 ± 0.7 ng/10⁷ cells of LTB₄ measured by radioimmunoassay. However, the maximum aggregation of PMNs achieved by exposure to LTB₄ (10⁻⁷M) was only 50% of that produced by maximally aggregating concentrations of PAF (10⁻⁷M). 5-Lipoxygenase inhibitors, BW755c and Nafazatrom at concentrations that completely abolished LTB₄ synthesis inhibited the aggregation induced by PAF only by 40% and 50% respectively. Furthermore, desensitisation experiments revealed that the aggregatory response of PMNs to PAF was only partially refractory to prior treatment with LTB₄ whereas the aggregatory response to LTB₄ was completely refractory to prior treatment with PAF. These results suggest that PAF-induced aggregation of rat PMNs is in part mediated by LTB₄ and in part directly by an as yet unidentified mechanism.     

Separation and concentration of Δ-6-keto-PGF1α using monoclonal antibody to ω3-olefin structure of trienoic prostanoids

A monoclonal antibody against cis-3-hexen-1-ol was prepared and used to separate and/or concentrate Δ¹⁷-6-keto-prostaglandin F_1α (PGF_1α) in the human sera. cis-3-Hexen-1-ol was conjugated with the human serum albumin (HSA) according to the N-succinimidylester method and hyperimmunized to BALB/c mouse. The monoclonal afntibodies were obtained from hybridoma clones established by a fusion between SP2/0-Ag14-k13 mouse myeloma cells and splenocytes of a mouse. A monoclonal antibody, named 4G9-12B, recognized the epitope characteristic for ω3-olefin structure. The 4G9-12B antibody became more specific for Δ¹⁷-6-keto-PGF_1α than 6-keto-PGF_1α by applying inhibition ELISA using amino-residue coating plates. Using the prepared immunoaffinity columns of this antibody, Δ¹⁷-6-keto-PGF_1α was clearly detected in 6 pg/ml of the human blood sera by GC/MS analysis. These results suggest that the monoclonal antibody to the partial structure of trienoic prostanoid, ω3-olefin unit, and that its immunoaffinity columns are useful in separating and concentrating Δ¹⁷-6-keto-PGF_1α in the human blood or urine.     

Differential steric effects in the axial ligation of pyridine and imidazole to α- and β-alkylcobinamides

One subclass of B₁₂-requiring enzymes is now known to bind their B₁₂ coenzymes “base-off,” with a histidine residue from the protein supplying an imidazole ligand to the cobalt center. Recent results from Sirovatka and Finke (J.M. Sirovatka and R.G. Finke, J.Am. Chem. Soc. 119, (1997) 3057) show that imidazole has an extraordinary trans effect on the mode of carbon–cobalt bond cleavage in coenzyme B₁₂ analogs, compared to pyridine or the natural 5,6-dimethylbenzimidazole ligand, and it was suggested that a differential steric effect could, in part, account for the uniqueness of the imidazole ligand. Such a differential steric effect for imidazole and pyridine is now demonstrated by studies of the thermodynamics of ligation of these ligands to the α and β diastereomers of two alkylcobinamides (RCbi⁺s, derivatives of cobalamins which lack the normal axial nucleotide) based on the known differences in steric crowding of the α (“lower”) and β (“upper”) axial ligand positions of cobalt corrinoids. Imidazole binds more tightly than pyridine to both diastereomers of NCCH₂Cbi⁺ and CF₃Cbi⁺, in all cases due to a more favorable entropy change, which is the result of lowered steric interference with corrin side chain thermal motions.     

Pharmacological characterization of the biosynthesis of prostanoids and hydroxyeicosatetraenoic acids in human whole blood and platelets by targeted chiral lipidomics analysis

Platelet 12-lipoxygenase(p-12-LOX) is highly expressed in human platelets, and the development of p-12-LOX inhibitors has the potential to be a novel antithrombotic tool by inhibiting thrombosis without prolonging hemostasis. A chiral liquid chromatography-mass spectrometry(LC-MS/MS) method was used to assess the impact of three commercially available LOX inhibitors[esculetin(6,7-dihydroxycoumarin), ML-355(N-2-benzothiazolyl-4-[[(2-hydroxy-3-methoxyphenyl)methyl]amino]-benzenesulfonamide), CDC(cinnamyl-3,4-dihydroxy-α-cyanocinnamate) and acetylsalicylic acid(ASA; a cyclooxygenase-1 inhibitor) on the generation of prostanoids and HETEs(hydroxyeicosatetraenoic acids) in human whole blood allowed to clot for 1 h at 37 °C(serum), platelet-rich plasma(PRP) stimulated with collagen or TRAP-6(a peptide activating thrombin receptor) and washed platelets. In serum, ML-355 did not affect eicosanoid generation, while CDC caused an incomplete reduction of 12S-HETE levels; esculetin inhibited both 12S-HETE and thromboxane(TX)B₂ production; ASA selectively affected TXB₂ production. In washed platelets stimulated with thrombin, esculetin, and CDC inhibited both 12S-HETE and TXB₂ while ML-355 was almost ineffective. In PRP, ML-355, CDC, and esculetin did not affect platelet aggregation associated with incomplete effects on eicosanoid biosynthesis. ASA alone or in combination with ticagrelor(a P2Y₁₂ blocker) affected platelet aggregation associated with profound inhibition of TXB₂ generation. P2Y₁₂ receptor signaling contributed to platelet 12S-HETE biosynthesis in response to primary agonists. In conclusion, ML-355, esculetin, and CDC were not selective inhibitors of p-12-LOX in different cellular systems. They did not affect platelet aggregation induced in PRP by collagen or TRAP-6. The characterization of 12-LOX inhibitors on eicosanoids generated in human whole blood is useful for information on their enzyme selectivity, off-target effects, and the possible influence of plasma components on their pharmacological effects.     

Formation of leukotrienes and hydroxy acids by human neutrophils and platelets exposed to monosodium urate

Monosodium urate (MSU) crystals stimulate the production of arachidonic acid metabolites by human neutrophils and platelets. Neutrophils exposed to MSU generated leukotriene B₄(LTB₄). 6- -LTB₄, 12- -6- -LTB₄, and 5S, 12S DHETE from endogenous sources of arachidonate. In addition to these metabolites both monohyroxyeicosatetraenoic acids (i.e., 5-HETE) and w-oxidation products (i.e., 20-COOH LTB₄) were formed by neutrophils exposed to MSU. Addition of exogenous arachidonic acid led to increased formation of each of these metabolites. When neutrophils were treated with colchicine (10 uM), LTB₄ but 5-HETE formation was impaired. (1-¹⁴C) Arachidonate-labeled platelets exposed to MSU released (1-¹⁴C)-arachidonate. (¹⁴C)-12 HETE, (¹⁴C)-HHT and (¹⁴C)-thromboxane B₂. Results indicate that MSU stimulates arachidonic acid metabolism in both human neutrophils and platelets. Moreover, they suggest not only that metabolites of arachidonate may be considered as possible candidates for mediators of inflammation in crystal-associated diseases, but that colchicine blocks the formation of LTB₄.     

Prostaglandin D2 metabolite stimulates collagen synthesis by human osteoblasts during calcification

We investigate the effect of the prostaglandin D₂ metabolite Δ¹²−PGD₂ (9−Deoxy−Δ⁹, Δ¹²−13,14-dihydroprostaglandin D₂) on collagen synthesis in human osteoblast. Δ¹²-PGJ₂ at 10⁻⁵M enhanced collagen synthesis in the presence of 2 mM α-glycerophosphate-2Na. The stimulative effect appeared as early as 3 days after addition and continued until 22 days. The enhancement of type I collagen synthesis was confirmed by polyacrylamide gel electrophoresis. The potency was the same as 10^1t-8M 1 α, 25 dihydroxy vitamine D₃ (1,25(OH)₂D₃). Northern blot analysis showed that 10⁻⁵M Δ ¹²-PGD₂ and 10⁻⁸M 1,25(OH)₂D₃ enhanced the transcribtion of type 1 procollagen (α₁) mRNA levels in osteoblasts.     

A radioimmunoassay for leukotriene B4

A radioimmunoassay for leukotreine B₄ has been developed. The assay is sensitive; 5 pg LTB₄ caused significant inibition of binding of [³H]-LTB₄ and 50% displacement occurred with 30 pg. The specificity of the assay has been critically examined; prostaglandins, thromboxane B₂ and arachidonic acid do not exhibit detectable cross-reactions (< 0.03%). Flowever, some non-cyclic dihydroxy- and monohydroxy-eicosatetraeonic acids do cross-react slightly (e.g. diastereomers of 5,12-dihydroxy-6,8,10-$\text{trans}$-14-$\text{cis}$-elcosatetraenoic and 12-hydroxy-5,8,10,14-elcosatetraenoic acids cross-react 3.3% and 2.0% respectively). The assay has been used to monitor the release of LTB₄ from human neutrophils in response to the divalent cation ionophore, A23187. The immunoreactive material released during these incubations was confirmed as LTB₄ by reverse-phase high liquid chromatography follwing solvent extraction and silinic acid chromatography.     

Modulation of KCa3.1 Channels by Eicosanoids,Omega-3 Fatty Acids,and Molecular Determinants

Background

Cytochrome P450- and ω-hydrolase products (epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraeonic acid (20-HETE)), natural omega-3 fatty acids (ω3), and pentacyclic triterpenes have been proposed to contribute to a wide range of vaso-protective and anti-fibrotic/anti-cancer signaling pathways including the modula-tion of membrane ion channels. Here we studied the modulation of intermediate-conductance Ca²⁺/calmodulin-regulated K⁺ channels (K_Ca3.1) by EETs, 20-HETE, ω3, and pentacyclic triterpenes and the structural requirements of these fatty acids to exert channel blockade.

Methodology/Principal Findings

We studied modulation of cloned human hK_Ca3.1 and the mutant hK_Ca3.1^V275A in HEK-293 cells, of rK_Ca3.1 in aortic endothelial cells, and of mK_Ca3.1 in 3T3-fibroblasts by inside-out and whole-cell patch-clamp experiments, respectively. In inside-out patches, Ca²⁺-activated hK_Ca3.1 were inhibited by the ω3, DHA and α-LA, and the ω6, AA, in the lower µmolar range and with similar potencies. 5,6-EET, 8,9-EET, 5,6-DiHETE, and saturated arachidic acid, had no appreciable effects. In contrast, 14,15-EET, its stable derivative, 14,15-EEZE, and 20-HETE produced channel inhibition. 11,12-EET displayed less inhibitory activity. The K_Ca3.1^V275A mutant channel was insensitive to any of the blocking EETs. Non-blocking 5,6-EET antagonized the inhibition caused by AA and augmented cloned hK_Ca3.1 and rK_Ca3.1 whole-cell currents. Pentacyclic triterpenes did not modulate K_Ca3.1 currents.

Conclusions/Significance

Inhibition of K_Ca3.1 by EETs (14,15-EET), 20-HETE, and ω3 critically depended on the presence of electron double bonds and hydrophobicity within the 10 carbons preceding the carboxyl-head of the molecules. From the physiological perspective, metabolism of AA to non-blocking 5,6,- and 8,9-EET may cause AA-de-blockade and contribute to cellular signal transduction processes influenced by these fatty acids.     

Optimization of a Propionibacterium acidipropionici continuous culture utilizing sucrose

To produce propionic acid and vitamin B₁₂ from sucrose, the strain Propionibacterium acidipropionici NRRL B3569 was selected by screening a number of Propionibacterium strains. The nutrient composition and the fermentation conditions for this strain were optimized in continuous culture. The investigations show that within a concentration range of 30–170 g l^–1 of sucrose in the fermentation medium, no significant substrate inhibition occurred. For the production of propionic acid and vitamin B₁₂, concentrations of 1.5 mg FeSO₄·7H₂O g^–1 dry biomass, 0.75 mg cobalt ions g^–1 dry biomass, 0.3 mg 5,6-dimethylbenzimidazole g^–1 dry biomass, and 12 g yeast extract 1^–1 were necessary additions to the sources of nitrogen, phosphate, and magnesium ions. The extra addition of up to 2.8 g betaine g^–1 dry biomass significantly increases the production of vitamin B₁₂. In the optimization of the pH value, temperature, and aeration, it was established that the conditions for propionic acid production and vitamin B₁₂ production are different. Whereas the optimal production of propionic acid took place under completely anaerobic conditions with a pH value of 6.5 and a temperature of 37°C, optimal vitamin B₁₂ production required a temperature of 40°C and aerobic conditions (0.5 vvm aeration at 100 rpm) with a pH value of 6.5.     

Purification and characterization of leukotriene A4 epoxide hydrolase from dog lung

Leukotriene A₄ epoxide hydrolase from dog lung, a soluble enzyme catalyzing the hydrolysis of leukotriene A₄ (LTA₄) to leukotriene B₄ (LTB₄) was partially purified by anion exchange HPLC. The enzymatic reaction obeys Michaelis- Menten kinetics. The apparent Km ranged between 15 and 25 μM and the enzyme exhibited an optimum activity at pH 7.8. An improved assay for the epoxide hydrolase has been developed using bovine serum albumin and EDTA to increase the conversion of LTA₄ to LTB₄. This method was used to produce 700 mg of LTB₄ from LTA₄ methyl ester. The partial by purified enzyme was found to be uncompetitively inhibited by divalent cations. Ca²⁺, Mn⁺, Fe²⁺, Zn⁺² and Cu⁺² were found to have inhibitor constants (Ki) of 89 mM, 3.4 mM, 1.1 mM, 0.57 mM, and 28 μM respectively Eicosapentaenoic acid was shown to be a competitive inhibitor of this enzyme with a Ki of 200 μM. From these inhibition studies, it can be theorized that the epoxide hydrolae has at least one hydrophobic and one hydrophilic binding site.