Fatty acid residues

Fig. 1. Chemical stmcture of phosphatidylcholine (PC) (1) and other related phosphohpids. R C O represents fatty acid residues. The choline fragment may be replaced by other moieties such as ethanolamine (2) to give phosphatidylethanolamine (PE), inositol (3) to give phosphatidylinositol (PI), serine (4), or glycerol (5). IfH replaces choline, the compound is phosphatidic acid (6). The corresponding lUPAC-lUB names ate (1), l,2-diacyl-t -glyceto(3)phosphocholine (2), l,2-diacyl-t -glyceto(3)phosphoethanolamine (3), 1,2-diacyl-t -glyceto(3)phosphoinositol (4), 1,2-diacyl-t -glyceto(3)phospho-L-serine and (5), l,2-diacyl-t -glyceto(3)phospho(3)-t -glycetol.

Acyl Side-Chain Reactions. Many reactions occur in the R group of the fatty acid residue (see Carboxylic acids Fats and fatty oils). 

Hydrogena.tlon. Lecithin can be hydrogenated. The resulting lecithins have only saturated fatty acid residues (palmitic or stearic acid) and are more or less colorless and crystalline. 

The melting points of even-numbered-carbon fatty acids increase with chain length and decrease according to unsaturation. A triacylglycerol containing three sam-rated fatty acids of 12 carbons or more is solid at body temperature, whereas if the fatty acid residues are 18 2, it is liquid to below 0 °C. In practice, natural acylglyc-erols contain a mixture of fatty acids tailored to suit their functional roles. The membrane lipids, which must be fluid at all environmental temperatures, are... 

B, phosphatidylethanolamine C, phosphatidylglycerol D, diphosphatidylglycerol (cardiolipin). Ra.COO and Rb.COO are fatty acid residues. 

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... 

Enzyme-catalyzed transfer of KDO from CMP-KDO (127) into a lipid-A acceptor has been studied by Heath and coworkers,1 using a cell-free system from Escherichia coli O 111 J-5. LPS from the organism did not function as an acceptor, and only weak acceptor-activity was displayed147-148 by lipid A preparations obtained by mild, acid-catalyzed hydrolysis of LPS. Base-catalyzed, hydrolytic removal of the ester-linked, but not the amide-linked, fatty acid residues from lipid A resulted in an acceptor of maximal activity1 (see Scheme 38 compare Scheme 39). 

Acyl migration refers to the movement of a fatty acid residue from one position on glycerol... 

Naimochelin C (Fig. 15, 54) from the myxobacterium Nannocystis exedens contains two L-Lys and two ( )-cinnamic acid units. The reported mono- and di-methyl esters (nannochelin B and A) may be artifacts from the work-up (198). A synthesis is described (29) (see Sect. 8.4). The ochrobactins (Fig. 15,55) isolated from the sea-shore bacterium Ochrobactrum sp. (214) with the spacer L-lysine are membrane active due to the fatty acid residues (saturated Cg and (2 )-unsaturated Cg and Cio) cf. lipopeptidic siderophores in Sect. 2.8. 

Fats are esters of the trivalent alcohol glycerol with three fatty acids. When a single fatty acid is esterified with glycerol, the product is referred to as a monoacylglycerol (fatty acid residue = acyl residue). 

The three acyl residues of a fat molecule may differ in terms of their chain length and the number of double bonds they contain. This results in a large number of possible combinations of individual fat molecules. When extracted from biological materials, fats always represent mixtures of very similar compounds, which differ in their fatty acid residues. A chiral center can arise at the middle C atom (sn -C-2) of a triacylglycerol if the two external fatty acids are different. The monoacylglycerols and diacylglycerols shown here are also chiral compounds. Nutritional fats contain palmitic, stearic, oleic acid, and linoleic acid particularly often. Unsaturated fatty acids are usually found at the central C atom of glycerol. 

The length of the fatty acid residues and the number of their double bonds affect the melting point of the fats. The shorter the fatty acid residues and the more double bonds they contain, the lower their melting points. 

Fats (triacylglycerols) are mainly attacked by pancreatic lipase at positions 1 and 3 of the glycerol moiety. Cleavage of two fatty acid residues gives rise to fatty acids and 2-mono-acylglycerols, which are quantitatively the most important products. However, a certain amount of glycerol is also formed by complete hydrolysis. These cleavage products are resorbed by a non-ATP-dependent process that has not yet been explained in detail. 

Ozone interactions with the membrane are believed to involve both critical sulfhydral groups and fatty acid residues and they may cause changes in the membrane s fluidity. 

In conclusion, it is our view that K+ plays a dominant role in maintaining a favorable plant cell water status and that the deleterious effects of ozone occur primarily due to disruption of this normal ionic balance. We currently visualize the following scheme of ozone damage (a) ozone attack of an SH group or fatty acid residue (b) permeability changes of the membrane leading to loss of both K" " and osmotic water (c) inhibition or loss of K" " pump activity for reacquisition of lost K+ (d) loss of a critical level of ion and (e) gross disruption of cellular metabolism. 

The location of the double bonds in unsaturated glycerophosphocholine (GPC) lipids is made difficult mainly due to the limited amounts of these compounds isolated from cells. When a thin layer of a GPC lipid is exposed to the action of ozone, partial or total ozonization of the unsaturated fatty acid residues may take place, depending on the particular compound being analyzed. The ozonized hpid is dissolved and analyzed by tandem MS. A typical injection into the instrument may be 5 xL containing 10-20 ng of the lipid. An illustrative example is the ozonized l-stearoyl-2-arachidonoyl-GPC, showing the systematic fragmentation pattern in Scheme 21, typical of the ozonized GPC lipids. Thus, the molecular peak appears increased by one nominal unit (M + H, m/e 1002),... 

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