Lipoxygenase actions

Free radicals are essential to many normal biological processes. They are involved in cyclo-oxygenase and lipoxygenase action in eicosanoid... 

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... 

Another processability factor is TOTOX value that is related to the degree of oil deterioration due to lipoxygenase action on polyunsaturated fatty acids in the oil (Mounts et al., 1990). Products of oxidation degrade flavor and stability of edible oils. A low TOTOX value <3.0 meq/kg is desirable. TOTOX was calculated as two times the peroxide value as determined by AOCS Method Ca9f-57 plus the anisidine value (AOCS, 1987). 

In E. foetidum a total of 13 aroma-active constituents with FD-factors > 9 were detected. These consisted of two n-aldehydes (nos. 2 and 6), seven 2-alkenals (nos. 3, 5, 7, 8, 9, 11, 28), (Z)-3-hexenal (no. 22) and three unknown compounds (nos. 29, 30 and 32)(Table V). All of these compounds were detected in C sativum with the exception of an unknown compound (no. 32) having a spicy, herbaceous note. ( )-2-Dodecenal was by far the predominant aroma component with an FD-factor of 2187. Unknown compound no. 30 had the second highest FD factor (=243). The musty, chlorine-like character of this compound may be important in the overall aroma of E. foetidum herb. Other aroma contributors include compounds with FD factors from 27 to 81, such as nos. 5, 6, 7, 11, 22, and 29. Despite having an FD factor of 27, (Z)-3-hexenal (no. 22) was probably derived via lipoxygenase action during sample preparation and may not be a characteristic aroma component of essential oil of E. foetidum herb. 

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). 

Lipoxygenases catalyse the regio-specific and stereoselective oxygenation of unsaturated fatty acids. The mammalian enzymes have been detected in human platelets, lung, kidney, testes and white blood cells. The leukotrienes, derived from the enzymatic action of the enzyme on arachidonic acid, have effects on neutrophil migration and aggregation, release of lysosomal enzymes, capillary permeability, induction of pain and smooth muscle contraction (Salmon, 1986). 

Payne, A.N., Jackson, W.P., Salmon, J.A., Nicholls, A., Yeadon, M. and Garland, L.G. (1991). Hydroxamic acids and hydroxyureas as novel, selective 5-lipoxygenase inhibitors for possible use in asthma. Agents Actions 34, 189-199. 

Interestingly, the release of PUFAs without subsequent action of a lipoxygenase can act as a wound-activated defense diatom in rich fresh water biofilms. This reaction could be directly associated with a chemical defense against the grazer Thamnocephalus platyurus [78]. 

Flavonoids exhibit protective action against LDL oxidation. It has been shown [145] that the pretreatment of macrophages and endothelial cells with tea flavonoids such as theaflavin digallate diminished cell-mediated LDL oxidation probably due to the interaction with superoxide and the chelation of iron ions. Quercetin and epicatechin inhibited LDL oxidation catalyzed by mammalian 15-lipoxygenase, and are much more effective antioxidants than ascorbic acid and a-tocopherol [146], Luteolin, rutin, quercetin, and catechin suppressed copper-stimulated LDL oxidation and protected endogenous urate from oxidative degradation [147]. Quercetin was also able to suppress peroxynitrite-induced oxidative modification of LDL [148],... 

Figure 6.17. Leukotriene formation in neutrophils. Arachidonic acid, which is released from membrane phospholipids by the action of either phospholipase A2 or diacylglycerol lipase (see Fig. 6.13), is oxygenated by 5-lipoxygenase to yield 5 hydroperoxy-6,8,11,14 eicosa-tetraenoic acid (5-HPETE). This is then converted into 5 hydroxy-6,8,11,14 eicosatetra-enoic acid (5-HETE) and leukotriene (LT) A4. LTA4 may then be enzymically converted into LTC4 and LTB4. LTB4 is the major product in activated neutrophils.

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