Fatty acids in phospholipids

Arachidonic acid is present in membranes and accounts for 5-15% of the fatty acids in phospholipids. Docosahexaenoic acid (DHA 0)3, 22 6), which is syn-... 

L. Zelles, Y. Bai, T. Beck, and F. Beese, Signature fatty acids in phospholipids and... 

The distribution of fatty acids in phospholipids is not random, with saturated fatty acids preferentially occupying position 1 and unsaturated fatty acids position 2. 

Fig. 3. Autoxidation of polyunsaturated fatty acids in phospholipid membranes. Addition of oxygen to lipid free radicals is extremely fast. It yields peroxyl radicals ROO which will tend to capture labile hydrogen atoms of neighbouring polyunsaturated lipids. Accidentally produced free radicals will therefore initiate a chain reaction of lipid peroxidation which will propagate along membranes. This process can result in several dozen propagation steps before it is stopped by a termination reaction. Examples of such termination reactions are the recombination of peroxyl radicals and the formation of a stable free radical from a free radical scavenger (scavH). Termination through recombination of low steady-state concentration of alkyl radicals is unlikely in aerobic medium.

Most of these effects of vitamin E deficiency can be attributed to membrane damage. In deficiency, there is an accumulation of lysophosphatidylcholine in membranes, which is cytolytic. The accumulation of lysophosphatidylcholine is a result of increased activity of phospholipase A. It is not clear whether a-tocopherol inhibits phospholipase A whether there is increased phospholipase activity because of increased peroxidation of polyunsaturated fatty acids in phospholipids, and hence an attempt at membrane Upid repair or whether the physicochemical effects of a-tocopherol on membrane organization and fluidity prevent the cytolytic actions of lysophosphatidylcholine (Douglas et al., 1986 Erin et al., 1986). 

Phosphatidylcholine contained the highest amount of unsaturated fatty acids, mostly oleic and linoleic acids. The other two principal phospholipids were rich in palmitic, linoleic, and linolenic acids. The presence of highly unsaturated fatty acids in phospholipids is important as they are prone to oxidation and can cause accelerated deterioration of the oil. It was also reported that phospholipids have a tendency to complex heavy metals, and these complexes are a stable form of catalyst, which can initiate and stimulate oxidation (28). 

Cis versus trans. Why might most unsaturated fatty acids in phospholipids be in the cis rather than the trans conformation Draw the structure of a 16-carbon fatty acid as (a) saturated, (b) trans monounsalurated, and (c) cis monounsaturated. 

In another research article, Wang et al. [20] successfully applied LC-MS metabonomic techniques to the metabolite profiling of plasma phospholipids in type 2 diabetes mellitus (DM2) patients. Diabetes mellitus is associated with a metabolic disorder of lipid or fatty acid in phospholipids. The authors were not only able to differentiate between the samples from the DM2 patients and the healthy subjects but also identified a number of phospholipid molecular species that could be used as potential biomarkers for a differentiation of DM2 patients from the healthy individuals and perhaps even an early detection of DM2. 

Fatty acids consist of a hydrocarbon chain attached to a carboxyl group (—COOH). They differ In length, although the predominant fatty acids In cells have an even number of carbon atoms, usually 14, 16, 18, or 20. The major fatty acids in phospholipids are listed in Table 2-3. Fatty acids often are designated by the abbreviation Cx y, where x is the number of carbons in the chain and y Is the number of double bonds. Fatty acids containing 12 or more carbon atoms are nearly insoluble in aqueous solutions because of their long hydrophobic hydrocarbon chains. 

The major fatty acids in phospholipids contain 14, 16, 18, or 20 carbon atoms and include both saturated and unsaturated chains (see Table 18-1). Saturated fatty acids... 

It is generally accepted that Ca + mobilization is crucial for the activation of phospholipases. However, Sevanian and coworkers (Sevanian et al., 1981 Sevanian and Kim, 1985) demonstrated that phospholipase A2 can also be activated in the absence of elevated Ca + by the presence of peroxi-dized fatty acids in phospholipids. The degree of phospholipase activation was correlated with the extent of TBARS. Thus, both peroxidized fatty acids and Ca + can independently trigger degradation of membrane lipids, but may also act syner-... 

Oxidation of polyunsaturated fatty acids (PUFA) in lipoproteins may be mediated by reactive species such as radicals, transition metals, other electrophiles, and by enzymes. Once initiated, oxidation of lipids may proceed by a chain reaction, illustrated in Fig. 4 (R5). In step I, an oxidant captures an electron from a PUFA to produce a lipid radical. In step 2, after rearrangement, the conjugated diene radical reacts rapidly with singlet oxygen to produce a lipid peroxide radical, which is the kinetically preferred reaction (step 3) (B5). The chain can be terminated if the lipid radical reacts with an antioxidant to produce a stable peroxide (step 4). Otherwise, the peroxyl radical can react with another polyunsaturated fatty acid as shown in step 5 to perpetuate a chain reaction. The chain reaction requires production of lipid peroxides, giving it the name peroxidation. Fatty acids oxidized in the core are largely triglycerides and cholesterol esters, while toward the outer layer fatty acids in phospholipids are oxidized. 

It is relatively rare to find significant quantities of both odd chain length and branched chain fatty acids in biological systems. However such compounds have been Isolated and identified from the epicuticular wax from Brussels sprout leaves, with anteiso-C j and anteiso-C making up 36% of the total saturated fatty acid fraction (13). Similarly Radunz has isolated and identified iso and anteiso mono methyl branched fatty acids in phospholipids, contained in yellow-white leaves and petals of the plastome mutants "Prasinizans" of Antirrhinum majus and "Xanthr of Nicotiana tabacum M4T In addition small amounts of odd chain length fatty acids and alcohols have been found in the surface waxes of Zea mays husks (15). 

The polyunsaturated fatty acids in phospholipids associated with the fish membranes also oxidize faster than the triacylglycerols found in fat deposits. Lipid oxidation in fish is influenced by several factors discussed below. 

Conjugated Fatty Acids in Phospholipids (% of total fatty acids)... 

The detailed metaboUsm of each fatty acid in phospholipid subclasses under thrombin or ionophore stimulation was also different as far as DHA is concerned. The pattern of EPA appeared quite superimposable on that of arachidonic acid, the main features being a decrease in both phosphatidylinositol and phosphatidylcholine and a weak reacylation into phosphatidyl-ethanolamine, at least for arachidonic acid. In contrast and unexpected from the results obtained with total phospholipids, one-fourth of DHA incorporated into phosphatidylcholine was Uberated and reacylated into phosphatidylethanolamine in a reciprocal way. 

Specific sources of vitamin E (ctlphn-tocopherol) include carrots, squash, broccoli, sweet potatoes, tomatoes, kale, cantaloupe melon, peaches and apricots. Vitamin E (Figure 9.19) is the main lipid-soluble antioxidant. It occurs in cell membranes together with polyunsaturated fatty acids in phospholipids, and vegetable oils (especially those rich in polyunsaturated fatty acids) are a major dietary source. It is a phenolic antioxidant, as are most natural antioxidants. 

Carrier, A. Parent, J. Liquid chromatography-mass spectrometry determination of free fatty acids in phospholipid-based formulations, J.Liq.Chromatogr.Rel.Technol., 2001, 24, 97-107. [stearic acid linoleic acid linolenic acid palmitic acid oleic acid]... 

Fatty acids in phospholipids are important for maintaining the function and integrity of cellular and subcellular membranes. These acids also play a role in the regulation of cholesterol metabolism—especially its transport, breakdown, and ultimate excretion. In addition, fatty acids have been shown to be the precursors for a group of hormonelike compounds called prostaglandins, which are important in the regulation of widely diverse physiological processes. 

ON THE FUNCTION OF METHYL-BRANCHED CHAIN FATTY ACIDS IN PHOSPHOLIPIDS OF CELL MEMBRANES OF HIGHER PLANTS... 

DLA Phosphorescence of Eosin-labeled Fatty Acids in Phospholipid Bilayers... 

Murata N, Sato N, Takahashi N, Hamazaki Y. Compositions and Positional Distributions of Fatty Acids in Phospholipids from Leaves of Chilling-Sensitive and Chilling-Resistant Plants. Plant and Cell Physiol. 1982 23(6) 1071-1079. 

X-ray crystallography). Products of arachidonate metabolism via the 15-lipoxygenase pathway have been involved in hyperalgesia and inflammation, while the 15-lipoxygenase-catalyzed oxygenation of es-terified fatty acids in phospholipids and in low-density lipoproteins has been implicated in the maturation of reticulocytes to erythrocytes and in the etiology of atherosclerosis (see, for review, ref. 145). 

Barnathan, G., Kornprobst, J.M., Doumenq, P., Miralles, J., and Boury-Esnault, N. (1993b) Sponge fatty acids 5. Characterization of complete series of 2-hydroxy long-chain fatty acids in phospholipids of two Senegalese marine sponges from the family Suberitidae Pseudosuberites sp. and Suberites massa.J. Nat. Prod., 56, 2104-2113. 

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