Lipoxygenase, hydroperoxidation

Wichard T, Pohnert G (2006) Formation of Halogenated Medium Chain Hydrocarbons by a Lipoxygenase/Hydroperoxide Halolyase-Mediated Transformation in Planktonic Microalgae. J Am Chem Soc 128 7114... 

Tressl et al. (16) proposed a enzymic pathway of C8-compounds from linoleic acid. Enzymes involved in the pathway are lipoxygenase, hydroperoxide lyase and oxidoreductase. The 13- and 9-hydroperoxides of linoleic acid were proposed as the products of lipoxygenase action and the precursors of C8-compounds. Enzymic reduction of l-octen-3-one to l-octen-3-ol in Aqaricus bisporus has been demonstrated (21), which is similar to the reaction of oxidoreductase mentioned by Tressl et al. (16). Wurzenberger and... 

CtHjjO, Mr 100.16. All isomers of H. occur in nature but only (25-3-H. [frequently accompanied by ( )-2-and ( )-3-H.] is practically ubiquitous, especially in firesh leaves and fruits cut into small pieces. They are formed, e.g., from linoleic or arachidonic acid enzymatically by lipoxygenases, hydroperoxide lyases, alcohol dehydrases, and sometimes isomerases. ... 

Aldehyde oxidase (superoxide ion) Glucose oxidase (superoxide ion) Xanthine oxidase (superoxide ion) Lipoxygenase (hydroperoxides, epoxides, free radicals)... 

Figure 4. Major fatty acid oxygenase pathways - lipoxygenase, hydroperoxide isomerase and lipoxins. Adapted from (37).

Wichard, T. and Pohnert, G. (2006) Formation of halogenated medium chain hydrocarbons by a lipoxygenase/hydroperoxide halolyase-mediated transformation in planktonic microalgae. J. Am. Chem. Soc., 128, 7114-7115. 

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... 

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]. 

An example of an experiment in which LDL has been treated with 15-lipoxygenase and the oxidation monitored by the formation of conjugated diene is shown in Fig. 2.2. In the absence of transition metal, a rapid increase in absorbance occurs, with no lag phase, which ceases after a period of about 90 min under these conditions. If copper is added to promote LDL oxidation at this point, LDL treated with lipoxygenase oxidizes at a faster rate with a short lag phase when compared to the control. During this procedure there is only a minimal loss of a-tocopherol and so we may ascribe the shortened lag phase to the increase in lipid peroxides brought about by lipoxygenase treatment. A similar result was found when LDL was supplemented with preformed fatty acid hydroperoxides (O Leary eta/., 1992). 

Garssen, G.J., Vliegenthart, J.F.G. and Boldingh, J. (1972). The origin and structures of dimeric fetty acids from the anaerobic reaction between soya-bean lipoxygenase, linoleic acid and its hydroperoxide. Biochem. J. 130, 435-442. 

Mechanisms of lipid peroxidation that have been implicated in atherosclerosis may be pertinent to RA. Cellular lipoxygenase enzymes may promote LDL modification by inserting hydroperoxide groups into unsaturated fetty-acid side chains of the LDL complex (Yla-Herttuala etal., 1990). 15-Lipoxygenase has been implicated as an initiator of LDL oxidation (Cathcart etal., 1991) whilst 5-lipoxygenase does not appear to be involved (Jessup et al., 1991). Products of activated lipoxygenase enzymes within inflammatory synovial fluid surest that this pathway could be activated in RA (Costello etal., 1992). 

FIG. 5 Rate of hydroperoxide production in (a, ) lipoxygenation in pure aqueous medium, (b, ) lipoxygenation in biphasic system, (c, x) two-enzyme (lipase-lipoxygenase) system in two-phase medium, determined experimentally, and (d, ) modeled kinetic of the two enzyme system. (From Ref 63.)... 

At the end of the reaction, hydroperoxide can be easily recovered in the aqueous phase (98-99%) after its separation from the organic phase and precipitation of the enzymes. The hydroperoxides obtained are highly reactive molecules [109]. They are intermediate compounds in the lipoxygenase pathway in plants, precursors for the synthesis of hydroxy-fatty acids (i.e., ( + )-coriolic acid [38,110], and regulators of the prostaglandins biosynthesis [111-113]. 

Yeum, K. J., Y. C. Leekim et al. (1995). Similar metabolites formed from beta-carotene by human gastric-mucosal homogenates, lipoxygenase, or linoleic acid hydroperoxide. Arch. Biochem. Biophys. 321(1) 167-174. 

PGH synthase and the related enzyme lipoxygenase occupy a position at the interface of peroxidase chemistry and free radical chemistry and can clearly trigger metabolic activation by both mechanisms. The peroxidase pathway activates compounds such as diethylstilbestrol and aromatic amines whereas the free radical pathway activates polycyclic hydrocarbons (59). Both pathways require synthesis of hydroperoxide in order to trigger oxidation. 

Schnurr et al. [22] showed that rabbit 15-LOX oxidized beef heart submitochondrial particles to form phospholipid-bound hydroperoxy- and keto-polyenoic fatty acids and induced the oxidative modification of membrane proteins. It was also found that the total oxygen uptake significantly exceeded the formation of oxygenated polyenoic acids supposedly due to the formation of hydroxyl radicals by the reaction of ubiquinone with lipid 15-LOX-derived hydroperoxides. However, it is impossible to agree with this proposal because it is known for a long time [23] that quinones cannot catalyze the formation of hydroxyl radicals by the Fenton reaction. Oxidation of intracellular unsaturated acids (for example, linoleic and arachidonic acids) by lipoxygenases can be suppressed by fatty acid binding proteins [24]. 

In contrast to numerous literature data, which indicate that protein oxidation, as a rule, precedes lipid peroxidation, Parinandi et al. [66] found that the modification of proteins in rat myocardial membranes exposed to prooxidants (ferrous ion/ascorbate, cupric ion/tert-butyl-hydroperoxide, linoleic acid hydroperoxide, and soybean lipoxygenase) accompanied lipid peroxidation initiated by these prooxidant systems. 

Glutathione peroxidase is a selenium-dependent enzyme, which rapidly detoxifies hydrogen peroxide and various hydroperoxides. Suttorp et al. [67] showed that the impairment of glutathione cycle resulted in an increase in the injury of pulmonary artery endothelial cells. Glutathione cycle protected against endothelial cell injury induced by 15-HPETE, an arachi-donate metabolite produced by 15-lipoxygenase-catalyzed oxidation [68]. 

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