Fatty acid side chains

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

It is easier to abstract a hydrogen atom and initiate lipid peroxidation from a fatty acid that has bis-allylic centres than from a fatty-acid side chain with only one double bond. It follows, therefore, that fatty-acid composition should influence the ability of a molecule such as LDL to act as a substrate for peroxidation. The potential... 

The initial drying of currently applied alkyd paints is accomplished by evaporation of solvent (physical drying). Subsequently, the eventual curing of the alkyd paint is completed by the formation of a polymer network, which is mainly formed by chemical crosslinks (oxidative drying) but in some cases also physical interactions between the fatty acid side chains occur, such as crystallization or proton-bridge formation [129]. Efficient network formation is crucial in the formation of dry films with good mechanical properties. Due to the presence of unsaturated units in the investigated LOFA- and TOFA-PHA bin-... 

The rate of production of DAG in the cell does not occur linearly with time, but rather it is biphasic. The first peak is rapid and transient and coincides with the formation of IP3 and the release of Ca2+ this DAG is therefore derived from the PI-PLC catalyzed hydrolysis of phosphatidylinositols [1]. There is then an extended period of enhanced DAG production that is now known to be derived from the more abundant phospholipid phosphatidylcholine (PC), which has a different composition of fatty acid side chains [9]. Although DAG may be generated directly from PC through the action of PC-PLC, it can also be formed indirectly from PC. In this pathway, PC is first hydrolyzed by PLD to give choline and phosphatidic acid, which is then converted to DAG by the action of a phos-phatidic acid phosphatase [10,11 ]. 

A fuUy unsaturated imidazop5Tidine acts as a platelet-aggregation inhibitor. The presence of the fatty acid side chain suggests a possible interaction with arachidonic... 

Fig. 10. A plot of the maximal relative activity (uRmax) of /3 hydroxybutyrate dehydrogenase-lecithin mixtures versus the number of carbon atoms in the saturated fatty acid side chains of the lecithins.

Phospholipid vesicles (and bilayers) composed of phospholipids with well-defined fatty acid side chains undergo a sharp transition from a crystallinelike state to an amorphous state as the temperature is raised.107 The transition temperature depends on the nature of the fatty acid side chains. For example, for C12 saturated fatty acid chains on lecithin the transition temperature is 0° and for C18 saturated fatty acid chains it is 58°C for unsaturated lecithins the transition temperature is below zero.107 For real membranes sharp phase transitions are not observed, because of the heterogeneous composition of the membrane. In the case of /3 hydroxybutyrate dehydrogenase, the enzymic activity apparently is not influenced by this phase transition as judged by the temperature dependence of the reaction rate. However, for some membrane-bound proteins, a plot of the reaction rate versus the reciprocal temperature... 

Here R, and R2 are long, fatty acid side chains. The parent fatty acids RjC02H and R2C02H usually have an even number of carbon atoms 16- and 18-carbon acids are the most common. The acid esterified to the hydroxyl group on C-l of the glycerol (that at the top of phosphatidylcholine is drawn above) usually has a fully saturated chain, whereas the acid attached at C-2 often has one or more double bonds, which are almost always cis double bonds. Table 17.1 lists some of the fatty acids commonly found in these positions. A phosphatidylcholine that has palmitic acid esterified at both the C-l and C-2 positions of the glycerol is known by... 

The amount of disorder in the fatty acid side chains in a phospholipid bilayer, as a function of temperature. The side chains become much more disordered as the temperature increases through the 7m. The solid curve represents a bilayer that does not contain cholesterol the dotted curve, a bilayer with the same phospholipid plus about 25% cholesterol. The amount of random, disorderly motion of the fatty acid chains can be measured quantitatively by deuterium- or l3C-NMR. At any given temperature, the disorder is greater near the tips of the chains (toward the middle of the bilayer) than it is close to the head-groups. 

A particularly damaging reaction is the reaction between the hydroxyl radical and unsaturated fatty acid side chains of phospholipids in the cell membrane, a reaction referred to as lipid peroxidation (Figure 2-17). 

Insulin detemir is a long-acting insulin analogue that lacks threonine at the B30 position and is acylated with a 14-carbon myristoyl fatty acid side-chain at the epsilon-amino group of the lysine in the B28 position. This stimulates binding to albumin and increases the half-life, extending its duration of action. 

Membrane lipids in brain contain high levels of polyunsaturated fatty acid side chains that are prone to free radical attack. 

Cholesterol probably orients such that its hydroxyl group is in the polar (aqueous) portion of the lipid bilayer, while its hydrocarbon portion is in the nonpolar (fatty acid side-chain) region. 

The TLR4-MD2 hetero-dimer has complex ligand specificity. It can be activated by structurally diverse LPS molecules, and minor changes in synthetic derivatives of LPS can abolish their endotoxic potency (Raetz and Whitfield, 2002 Rietschel et al., 1994). The diversity in potency of LPS is derived from variance within lipid A, as observed in both the number and the length of fatty acid side chains and the presence of terminal phosphate residues with a variety of modifications. Optimal lipid A potency is achieved with bi-phosphorylated, hexa-acylated, lipid A species (Raetz and Whitfield, 2002). Lipid A moieties that deviate from this pattern often demonstrate a significant decrease in endotoxic activity (Alexander and Rietschel, 2001). 

Because of its cylindrical shape and hydrophobic character, cholesterol is an important component of the membranes of animal cells. Its rigid structure decreases membrane fluidity, but it also inhibits the crystallization of fatty acid side chains of the membrane lipids and it acts as a sort of membrane plasticizer. 

L-serine. The latter three fragments arise by slow decomposition of a primary unit of 2-(2-hydroxy-6-methylphenyl)oxazoline. Acid hydrolysis also liberates /ra s-octadec-2-enoic acid, but the cis isomer is obtained by periodate cleavage and hence represents the natural configuration. The length of the n-A2-unsaturated fatty acid side chain ranges from C14 to C20 with Cig representing the main component (85%). No method has been found to separate mycobactins P with different side chains. Saponification yields mycobactic acid P and a neutral substance, cobactin P. Reductive hydrolysis in HI gives the hydroxyamino acid as L-lysine. 

Degradation procedures analogeus to those used for mycobactin P (see above) showed the aromatic residue to be salicylic acid (2-hydroxy-6-methylbenzoic acid in mycobactin P) and the hydroxy acid to be (+)-( -hydroxybutyric acid ((-)-3-hydroxy-2-methylpentanoic acid in mycobactin P). Fatty acid side chains substantially different from those in mycobactin P a minor component contains a s-octadec-2-enoic acid (identical to the principal product in mycobactin P). The major substituents in the fatty acid side chain are Cis to C21 fragments of unknown constitution. 

Physically, the membrane may exist in two states the "solid" gel crystalline and the "liquid" fluid crystalline states. For each type of membrane, there is a specific temperature at which one changes into the other. This is the transition temperature (Tc). The Tc is relatively high for membranes containing saturated fatty acids and low for those with unsaturated fatty acids. Thus, bilayers of phosphatidylcholine with two palmitate residues have a Tc = 41°C but that with two oleic acid residues has a Tc = -20°C. The hybrid has a Tc = -5°C. Sphingomyelin bilayer, on the other hand, may have a Tc of close to body temperature. In the gel crystalline state, the hydrophobic tails of phospholipids are ordered, whereas in the fluid crystalline state they are disordered. At body temperature, all eukaryotic membranes appear to be in the liquid crystalline state, and this is caused, in part, by the presence of unsaturated fatty acids and in part by cholesterol. The latter maintains the fatty acid side chains in the disordered state, even below the normal Tc. There is thus no evidence that membranes regulate cellular metabolic activity by changing their physical status from the gel to the fluid state,... 

Because cholesterol contains an -OH group, it is amphipathic. It controls membrane fluidity in mammals by inhibiting the ordering of fatty acid side chains, but it is absent from bacterial plasma membranes. 

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