Substrate lipoxygenase

Substrate Lipoxygenase Ce-aldehyde- forming activity Relative activity ( % ) Product ... 

Lipoxygenase-Catalyzed Oxidations. Lipoxygenase-1 catalyzes the incorporation of dioxygen into polyunsaturated fatty acids possessing a l(Z),4(Z)-pentadienyi moiety to yield ( ),(Z)-conjugated hydroperoxides. A highly active preparation of the enzyme from soybean is commercially available in purified form. From a practical standpoint it is important to mention that the substrate does not need to be in solution to undergo the oxidation. Indeed, the treatment of 28 g/L of linoleic acid [60-33-3] with 2 mg of the enzyme results in (135)-hydroperoxide of linoleic acid in 80% yield... 

In cell free systems or isolated cells, some enzymes of the arachidonate cascade can also recognize AEA and 2-AG as substrates, thereby producing the corresponding lipoxygenase and cyclooxygenase-2 derivatives. However, these metabolites have not yet been isolated from tissues and their biological relevance is still unknown. 

Triggering of asthma attacks in asthmatics. This side effect is a pseudo-allergic reaction where COX-inhibition increases the availability of substrates for lipoxygenase, which are converted to broncho-constrictive leukotriens... 

Applications of peroxide formation are underrepresented in chiral synthetic chemistry, most likely owing to the limited stability of such intermediates. Lipoxygenases, as prototype biocatalysts for such reactions, display rather limited substrate specificity. However, interesting functionalizations at allylic positions of unsaturated fatty acids can be realized in high regio- and stereoselectivity, when the enzymatic oxidation is coupled to a chemical or enzymatic reduction process. While early work focused on derivatives of arachidonic acid chemical modifications to the carboxylate moiety are possible, provided that a sufficiently hydrophilic functionality remained. By means of this strategy, chiral diendiols are accessible after hydroperoxide reduction (Scheme 9.12) [103,104]. 

There are three groups of eicosanoids that are synthesized from C20 eicosanoic acids derived from the essential fatty acids linoleate and a-linolenate, or directly from dietary arachidonate and eicosapentaenoate (Figure 23-5). Arachidonate, usually derived from the 2 position of phospholipids in the plasma membrane by the action of phospholipase Aj (Figure 24-6)—but also from the diet—is the substrate for the synthesis of the PG2, 1X2 series (prostanoids) by the cyclooxygenase pathway, or the LT4 and LX4 series by the lipoxygenase pathway, with the two pathways competing for the arachidonate substrate (Figure 23-5). 

The volumetric ratio of the two liquid phases (j6 = Forg/ Faq) can affect the efficiency of substrate conversion in biphasic media. The biocatalyst stability and the reaction equilibrium shift are dependent on the volume ratio of the two phases [29]. In our previous work [37], we studied the importance of the nonpolar phase in a biphasic system (octane-buffer pH 9) by varying the volume of solvent. The ratio /I = 2/10 has been the most appropriate for an improvement of the yield of the two-enzyme (lipase-lipoxygenase) system. We found that a larger volume of organic phase decreases the total yield of conversion. Nevertheless, Antonini et al. [61] affirmed that changes in the ratios of phases in water-organic two-phase system have little effect upon biotransformation rate. 

Lipoxygenase (EC 1.13.11.12, nonheme iron dioxygenase), the substrate (polyunsaturated fatty acid) is poorly water soluble and the product (hydroperoxy-fatty acid) is hydrophilic. The reaction occurs in the aqueous phase [85,86]. 

We previously described [25] the function of soybean lipoxygenase-1 in a biphasic system (modified Lewis cell) composed of an aqueous phase (borate buffer) and octane. The substrate of the reaction is linoleic acid (LA) and the main product is hydro-peroxyoctadecadienoic acid (LIP). The system involves two phenomena LA transfer from the organic to the aqueous phase and lipoxygenase kinetics in the aqueous medium. 

The kinetics of the lipoxygenase was studied in aqueous media [25]. The affinity of the enzyme for its substrate LA is very high. When LA is in excess in the medium it becomes the inhibitor of the reaction [Fig. 5(a)]. HP is also competitive inhibitor. The experimentally determined kinetic constants are ... 

However, in the two-phase system described here the reaction progress has an influence on substrate transfer [Eq. (9)] and steady-state changes continually during the evolution of the system. Interaction between the reactant transfer and lipoxygenase-catalyzed reaction is therefore studied in octane-aqueous biphasic medium (modified Lewis cell). 

The presence of the second enzyme in the medium accelerates and increases consumption of the first substrate (trilinolein), because lipoxygenase reacts with the second substrate (linoleic acid) produced by lipolysis of trilinolein. 

Hydroperoxides play an important role as oxidants in organic synthesis [56-58]. Although several methods are available for the preparation of racemic hydroperoxides, no convenient method of a broad scope was until recently [59] known for the synthesis of optically active hydroperoxides. Such peroxides have potential as oxidants in the asymmetric oxidation of organic substrates, currently a subject of intensive investigations in synthetic organic chemistry [60, 61]. The application of lipoxygenase [62-65] and lipases [66,67] facilitated the preparation of optically active hydroperoxides by enzymes for the first time. 

Arachidonic acid is a regular constituent of cell membrane phospholipids it is released by phospholipase A2 and forms the substrate of cyclooxygenases and lipoxygenases. 

This selenium-dependent enzyme [EC 1.11.1.9] catalyzes the reaction of two molecules of glutathione with hydrogen peroxide to produce glutathione disulfide and two water molecules. Hydrogen peroxide can be replaced by steroid and lipid hydroperoxides, albeit not as effectively (nevertheless, this enzyme is not identical with phospholipid-hydroperoxide glutathione peroxidase [EC 1.11.1.12]). However, the hydroperoxy products formed by the action of lipoxygenase [EC 1.13.11.12] are not substrates. 

NSAIDs usually do not inhibit lipoxygenase activity at concentrations that inhibit COX activity. In fact, by preventing arachidonic acid conversion via the COX pathway, NSAIDs may cause more substrate to be metabolized through the lipoxygenase pathways, leading to an increased formation of the inflammatory leukotrienes. Even among the COX-dependent pathways, inhibiting the... 

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