Phospholipid fatty acid residues

The intracellular and plasma membranes have a complex structure. The main components of a membrane are lipids (or phospholipids) and different proteins. Lipids are fatlike substances representing the esters of one di- or trivalent alcohol and two aliphatic fatty acid molecules (with 14 to 24 carbon atoms). In phospholipids, phosphoric acid residues, -0-P0(0 )-O-, are located close to the ester links, -C0-0-. The lipid or phospholipid molecules have the form of a compact polar head (the ester and phosphate groups) and two parallel, long nonpolar tails (the hydrocarbon chains of the fatty acids). The polar head is hydrophihc and readily interacts with water the hydrocarbon tails to the... 

Peroxyl radicals are the species that propagate autoxidation of the unsaturated fatty acid residues of phospholipids (50). In addition, peroxyl radicals are intermediates in the metabolism of certain drugs such as phenylbutazone (51). Epoxidation of BP-7,8-dihydrodiol has been detected during lipid peroxidation induced in rat liver microsomes by ascorbate or NADPH and during the peroxidatic oxidation of phenylbutazone (52,53). These findings suggest that peroxyl radical-mediated epoxidation of BP-7,8-dihydrodiol is general and may serve as the prototype for similar epoxidations of other olefins in a variety of biochemical systems. In addition, peroxyl radical-dependent epoxidation of BP-7,8-dihydrodiol exhibits the same stereochemistry as the arachidonic acid-stimulated epoxidation by ram seminal vesicle microsomes. This not only provides additional... 

The organic treatment had higher microbial biomass C and N, enzyme activity and potentially mineralisable N (Cunapala and Scow 1998) and different microbial community composition phospholipid fatty acid than the conventional treatment (Bossio ef al. 1 998). There were minimal differences between treatments in residue decomposition (Cunapala et al. 1998). Cover crops and higher irrigation frequency in the organic treatment may have contributed to the differences (Cunapala and Scow 1998). 

Fang X, Jin F, Jin H, von Sonntag C (1998) Reaction of the superoxide radical with the A/-centered radical derived from N-acetyltryptophan methyl ester. J Chem Soc Perkin Trans 2 259-263 Ferreri C, Costantino C, Landi L, Mulazzani QG, Chatgilialoglu C (1999) The thiyl radical-mediated isomerisation of c/s-monounsaturated fatty acid residues in phospholipids a novel path of membrane damage Chem Commun 407-408... 

Sprinz H, Adhikari S, Brede O (2001) Transformation of phospholipid membranes by thiyl radicals via ds-tmns isomerization in fatty acid residues. Adv Colloid Interface Sci 89/90 313-325 Stefanic I, Bonifacic M, Asmus K-D, Armstrong DA (2001) Absolute rate constants and yields of transients from hydroxyl radical and H atom attack on glycine and methyl-substituted glycine anions. J Phys Chem A 105 8681-8690... 

The lipid composition of membranes can vary in the same manner. Major components of prokaryotic membrane lipids are phospholipids and gly-colipids eukaryotic membrane lipids typically contain these two classes and, in addition, sterols such as cholesterol, and sphingolipids. Table III-3 gives the lipid content of some membranes from various sources. Table III-3 does not list some of the unusual and less abundant lipids found in membranes, such as lipamino acids, glycolipids, and phos-phatides containing unusual fatty acid residues. 

Ferreri C, Costantino C, Perrotta L, Landi L, Mulazzani QG, ChatgiKaloglu C. (2001) Cis-trans isomerization of polyunsaturated fatty acid residues in phospholipids catalyzed by thiyl radicals. J Am Chem Soc 123 4459 468. 

The many nonpolar C-C and C-H bonds of vitamin E make it fat soluble, and thus it dissolves in the nonpolar interior of the cell membrane, where it is thought to inhibit the oxidation of the unsaturated fatty acid residues in the phospholipids. Oxidative damage to lipids in cells via radical mechanisms is thought to play an important role in the aging process. For this reason, many anti-aging formulas with antioxidants like vitamin E are now popular consumer products. 

All glycerylphospholipids are considered as derivatives of sn-glyceryl-3-phosphoric acid that is acylated by two moieties of acjd-CoA producing 1,2-diacyl->yn-glyceryl-3-phosphoric acid. The mechanism of substitution of glyecrylphosphate of naturally occurring phospholipids produces phosphatidic acids with saturated or monounsaturated fatty acid residue in sn-l position and polyunsaturated acyl residue in sn-2 position Fig. (6). 

The fatty acid residues have usually even number of carbon atoms in the chains, ranging from 14 to 24 carbons and the double bond, if present, assumes the cis configuration. The phospholipids of animal origin comprise mainly palmitic oleic, linoleic and arachidonic fatty acids, while the ones of plant origin ones have mainly palmitic, oleic and linoleic tatty acids. 

Phospholipase AjS (PLAjs) hydrolyze the sn-1 fatty acid residue from phospholipids and produce mostly saturated or mono-unsaturated fatty acids and 2-acyl-lyso-phosphohpids. PLAjS have not attracted as much attention as mammalian acylhy-drolases, PLA2S, which are involved in the production of bio-active hpids such as prostanoids and platelet-activating factor (PAP) [1, 2]. 

Glycerophospholipids (PL) are abundant lipid components found in Nature [1]. Most vegetable oils, fish oil and egg yolk are particularly rich in mixtures of phospholipids. They are characterized by the presence of a polar head and two fatty acid chains in the apolar part of the molecule. The two acyl chains mainly consist of saturated fatty acid residues in the snl position and mainly (poly)unsaturated fatty acid chains in the sn2 position. Mixtures of phospholipids at low cost are obtained from the degumming process of vegetable oils. Lecithin, the main component of the mixture, has the polar head characterized by the choline residue. It is usually defined as phosphatidyl choline (PC) and it is understood that the composition of the apolar part is composed of mixtures of fatty acid residues dependent to a large extent on the source of the raw material (fatty acid chains composition of PC from soy beans palmitic 11.6%, stearic 3.4%, oleic 4.6%, linoleic 66.4%, linolenic 8.7%). Scheme 1 shows a PC with two defined acyl chains at the glycerol backbone l-palmitoyl-2-linoleoyl-5n-glycero-3-phosphocholine (PLPC). 

This reaction is responsible for formation of most of the cholesteryl ester in plasma. The preferred substrate is phosphatidylcholine, which contains an unsaturated fatty acid residue on the 2-carbon of the glycerol moiety. HDL and LDL are the major sources of the phosphatidylcholine and cholesterol. Apo A-I, which is a part of HDL, is a powerful activator of LCAT. Apo C-I has also been implicated as an activator of this enzyme however, activation may depend on the nature of the phospholipid substrate. LCAT is synthesized in the liver. The plasma level of LCAT is higher in males than in females. The enzyme converts excess free cholesterol to cholesteryl ester with the simultaneous conversion of lecithin to lysolecithin. The products are subsequently removed from circulation. Thus, LCAT plays a significant role in the removal of cholesterol and lecithin from the circulation, similar to the role of lipoprotein lipase in the removal of triacylglycerol contained in chylomicrons and VLDL. Since LCAT regulates the levels of free cholesterol, cholesteryl esters, and phosphatidylcholine in plasma, it may play an important role in maintaining normal membrane structure and fluidity in peripheral tissue cells. 

The isomer trends of the models were very useful for helping the identification of isomers. Cell cultures of human leukemia cell lines (THP-1) were incubated in the absence and presence of thiol compounds, ensuring that no trans compounds could come from the medium [45]. In parallel experiments, some millimolar levels of thiol compounds were added to the cell cultures during incubation, and the comparison of isomeric trends was carried out. A basic content of trans lipids in THP-1 cell membranes could be found during their growth without thiol, and after the addition of the amphiphilic 2-mercaptoethanol, it increased to 5.6% of the main fatty acid residues. Moreover, when a radical stress by y-irradiation is artificially produced in the cell cultures added with thiol, a larger isomerization effect could be seen, with trans lipid formation up to 15.5% in membrane phospholipids. The fatty acid residues most involved in this transformation were arachidonate moieties, as expected. 

We have previously mentioned that lipids make part of the membrane architecture, which has the typical bilayer arrangement due to the phospholipid supramo-lecular organization. This leads to biological consequences - the composition of fatty acid residues with saturated and unsaturated hydrocarbon chains is crucial to regulate membrane properties, maintaining the best balance for cellular functioning and also survival. Vesicle models made of phosphatidylcholines with saturated and unsaturated fatty acid residues are useful for studies of permeability and fluidity. Several studies have compared the effects of saturated, cis and trans unsaturated residues. An example is given in Fig. 6.4 for vesicles made up of different phospholipid compositions. 

Phospholipids are important components of biological membranes. Various classes of phospholipid occur, and within each class, a distribution of fatty acid residues is found. A variety of physical techniques have shown that a number of pure phospholipids undergo a transition from a crystalline to a liquid crystalline form at a temperature dependent upon the presence and type of unsaturation in the fatty acid residues. The implications of these results to the dispersibility of phospholipids in water, the formation of myelin tubes, the production of model membranes, and to the natural biological systems, are discussed. 

Differential Thermal Analysis Studies. Recent studies of pure anhydrous phospholipids (7) using differential thermal analysis (DTA) have revealed the existence of more than one thermal transition when a phospholipid is heated. Thus, 2,3-dimyristoyl-DL-phosphatidylethanolamine shows on heating a marked endothermic transition at about 120°C. and a smaller endothermic transition at about 135°C. (Figure 2). The major thermal transition is not immediately reversible with the phosphatidyl-ethanolamines, and even holding at room temperature for some days does not produce complete reversion to the original form. The transition with the phosphatidylcholines, in contrast, is lower for the same fatty acid residues and is reversible in character. When one of the chains is unsaturated with a cis group, as occurs with a phospholipid such as 3-stearoyl-2-oleoylphosphatidylethanolamine, the main endothermic transition occurs at a lower temperature, about 70°C. The transition temperatures for... 

We can envisage that the distribution of fatty acid residues observed with the phospholipids in biological tissues provides the correct fluidity at a particular environmental temperature to match the required diffusion or rate of metabolic processes required for the tissue. Thus in membranes where metabolic and diffusion processes must be rapid, such as in the mito-... 

Micellar systems are exceptionally convenient for the introduction of hydrophobic and low-water-soluble reagents into protein molecules in controlled quantities (first of all, of one or two hydrophobic residues per protein molecule) [74]. This method is successfully employed for the introduction of long-chain fatty acid residues [74-76], phospholipids [77],... 

The participation of lipids in the generation of potential on the membrane becomes most evident from a comparison of the results of experiments with bilayers formed from phospholipids containing nonsaturated or saturated fatty acid residues (chain 6) in air atmosphere or in an inert atmosphere ... 

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