Polyunsaturated fatty acid enzymatic oxidation

Polyunsaturated fatty acids are oxidized by enzymatic and nonenzymatic pathways. Nonenzymatic oxidation is a free-radical mediated peroxidation. It is a chain reaction providing a continuous supply of free radicals that initiate further peroxidation. The whole process can be depicted as follows [21] ... 

Cyanidin 3-O-b-D-glucoside (C3G) of a typical anthocyanin pigment could lower the serum thiobarbituric acid-reactive substance concentration and increase the oxidation resistance of the serum to lipid peroxidation in rats [52]. In vitro enzymatic and non-enzymatic polyunsaturated fatty acid per oxidation was significantly inhibited in a dose-dependent manner by anthocyanin [53], a deep-red color pigment from carrot cell cultures. 

Abstract. The significance of free radical oxidation of phospholipids in tissues of animals with experimental atherosclerosis was investigated. By using modem physico-chemical methods an elevated content of polyunsaturated fatty acids and other lipids peroxides was discovered in the blood and the aorta of rabbits with experimental atheromatosis. The human blood demonstrated a low level of protective enzymatic systems and a high content of products secondary to peroxidal oxidation of the lipids. The mechanism accounting for the action of lipids peroxides on the vascular wall resulting in the formation of atheromatous plaques is considered. 

The mild green-metallic-mushroom aroma of fresh fish is formed by enzymatic-oxidative degradation of polyunsaturated fatty acids (PUFA) with the participation of... 

It has been well established that fatty acid metabolites of LOX and cytochrome P450 are implicated in essential aspects of cellular signaling, including the induction of apoptosis. The enzymatic and non-enzymatic products of polyunsaturated fatty acids thus control cell growth and apoptosis, and the spontaneous oxidation of polyunsaturated fatty acids gives rise to reactive aldehydes and other products of lipid peroxidation that are potentially cytotoxic and which may also signal apoptosis [102]. 

Allyl)iron(III) complexes have been implicated in the enzymatic lipoxygenation of polyunsaturated fatty acids. In the proposed model, concerted allylic deprotonation and electrophilic addition see Electrophilic Reaction) of Fe gives an iron allyl species, which undergoes Fe-C bond insertion by O2. In model studies, reaction of allyltributyltin compounds with FeBrs, followed by exposure to oxygen, gives oxidation to the carbonyl compounds (26) through presumed intermediates (27). 

Fig. 6. Three irnportam oxidative pathways for the metabolism of polyunsaturated fatty acids. A. The principal steps in the formation of prostaglandin endoperoxides from arachidonic acid. B. Likely mechanism for the formation of hydroperoxy cis.trans conjugated fatly acids by autooxidalion or by lipoxygena.sc.s. In the latter case, positional as well as stereospecificity arc normally found. The formed hydroperoxides may then be enzymatically transformed into leukotrienes (not shown) or to hydroxy acids. C. The enzymatic sequence in cytochrome P-450 mediated oxygenation. The first electron is donated from NADPH via the f lavoprotein (Fp) NADPH-cytochrome-P-450-reductase. while the second electron comes either from NADPH or NADH. In this way the monooxygenase enzymes inlrrxluce one oxygen from air into the substrate.

Chapter 3 Enzymatic Oxidation of Polyunsaturated Fatty Acids.45... 

Lipoxygenase catalysed processes. Enzymatic bleaching of wheat flour by lipoxygenases is a widely practised operation in Europe and North America. The process is due to co-oxidation of carotenoids during oxygenation of polyunsaturated fatty acids such as linoleic acid to hydro-peroxy-octadecadienoic acid (Hildebrand and Hymowitz, 1982 Nicolas et al., 1982). The hydro-peroxy-octadecadienoic acids (HCDs) are key intermediary compounds for the synthesis of other important... 

Oxylipins are commonly found metabolites in higher plants and most of them originate from polyunsaturated fatty acid hydroperoxides by enzymatic transformations which have been extensively studied (for recent reviews, see 1,2). Two well characterized enzymes a lyase and an allene oxide synthase were shown to degrade hydroperoxides into compounds of physiological importance since they can ultimately yield fragrances or plant hormones such as jasmonic acid. We have recently reported a new fate for fatty acid hydroperoxides the peroxygenase pathway. It involves two enzyme activities i.e. a peroxygenase and an epoxide hydrolase which lead to the formation of epoxidized fatty acids and their derived dihydrodiols which are relevant to plant defense mechanisms. 

The fishy aroma of seafood is incorrectly attributed to trimethyl amine. Flavor formation in fresh and saltwater fish results from complex enzymatic, oxidative, and microbial reactions of n-3 polyunsaturated fatty acid precursors (e.g., eicosapentaenoic acid) (69,70). Hence, fish flavor is mostly composed of non-characterizing planty or melon-like aromas from lipid-derived unsaturated carbonyl compounds. Examples are (Z)-l,5-octadien-3-one ( geranium-like ) in boiled cod (71) and (7i,Z)-2,6-nonadienal ( cucumber-like ) in boiled trout (72). 

Fatty acids are oxidized by chemical or enzymatic mechanisms. Chemical oxidation is particularly important for polyunsaturated fatty acids and gives rise to the formation of free radicals which can, in turn, damage tissues. Similar peroxidation reactions can also be catalysed by lipoxygenase enzymes. 

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