Acyl chains polyunsaturated

Koenig BW. Strey HH, Gawrisch K. Membrane lateral compressibility determined by NMR and x-ray diffraction effect of acyl chain polyunsaturation. Biophys J 1997 73 1954—1966. 

High amounts of a,co-dicarboxylic acids (mainly suberic, azelaic and sebacic) in a paint sample are indicative of the presence of an aged drying oil. This is because dicarboxylic acids, of which azelaic is the most abundant, are produced during the auto-oxidation of the polyunsaturated acylic chain present in drying oils. 

Excitable membranes maintain and rapidly modulate substantial transmembrane ion gradients in response to stimuli 576 Specific lipid messengers are cleaved from reservoir phospholipids by phospholipases upon activation by various stimuli 576 Phospholipids in synaptic membranes are an important target in seizures, head injury, neurodegenerative diseases and cerebral ischemia 576 Some molecular species of phospholipids in excitable membranes are reservoirs of bioactive lipids that act as messengers 576 Mammalian phospholipids generally contain polyunsaturated fatty acyl chains almost exclusively esterified to the second carbon of glycerol 577... 

Rabinovich A. L. and Ripatti, P. O. (1991). On the conformational, physical properties and functions of polyunsaturated acyl chains, Biochim. Biophys. Acta-Lipid. Metahol, 1085, 53-62. 

Figure 12.11 Phosphoglyceride structure. The members of this group are derivatives of the parent compound, l,2-diacyl-src-glycerol-3-phosphate (phosphatidic acid) in which X is a hydrogen atom. This is replaced by either an amino alcohol or a polyhydroxy residue. In phosphoglycerides derived from animal tissues R1 is usually a saturated acyl chain of between 16 and 20 carbon atoms and R2 is usually unsaturated. Polyunsaturated acyl chains containing 16 or 18 carbon atoms predominate in leaf phosphoglycerides and those of bacterial origin are often more complex.

Figure 7. Relationship of oxidation and degree of polyunsaturation. Polyunsaturation is measured as the methylene bridge index (MBI), which is a more precise measure of extent of unsaturation and oxidizability than the double bond index. It is the mean number of 6is-allylic methylene bridge positions per fatty acid (or fatty acyl chain) in a lipid ensemble. The rate of lipid radical formation measures formation of an oxidative product, while O2 consumption (% O2 lost per sec) is a measure of utilization of a reactant. (Drawn using our data abstracted from Wagner, B.A., Buettner, G.R., and Bums, C.P. 1994, Biochemistry 33 4449-4453).

Three major families of unsaturated fatty acids are seen in warm-blooded animals, that is, the n-9, monounsaturated fatty acids (e.g. oleic acid, OA), and the n-6 and n-3, both polyunsaturated fatty acids (PUFAs). However, only the n-6 and n-3 families, derived from LA and ALA, respectively, are EFA. These must be obtained from the diet since mammals lack the desaturase enzymes necessary for the insertion of a double bond in the n-6 and n-3 positions of the fatty acid carbon chain. Fatty acid nomenclature is as follows The first number denotes the number of carbon atoms in the acyl chain and the second refers to the number of unsaturated (double) bonds. This is followed by a symbol n or co and a number that denotes the number of carbon atoms from the methyl terminal of the molecule to the first double bond. Hence, LA is 18 2(n-6), while the more unsaturated ALA is denoted as 18 3(n-3) (Figure 26.1). These fatty acids must be metabolized to their longer chain derivatives before carrying out many of their activities. 

A second important feature worth emphasizing is that the proton leak is affected by the lipid composition of the inner mitochondrial membrane. In general, the fatty acyl chains of phospholipid components of membranes can vary in their degree of unsaturation. The proton leak increases with the incorporation of polyunsaturated fatty acids (FAs) the greater the number of double bonds, the greater the proton leak (Hulbert and Else, 2000). As we shall note in the chapter on temperature relations, fatty acyl composition of membranes, including the inner mitochondrial membranes, changes in various... 

Interestingly, in addition to mitochondrial membrane differences, the properties of the plasma membranes in ectotherms compared to endotherms show similar differences in degrees of unsaturation of the phospholipid constituents. The higher proportion of polyunsaturated fatty acyl chains in endotherms in turn correlates with three- to four-fold higher Na+ and K+ background conductance and hence-higher... 

Another subtlety in double bond chemistry that is important in determining the effects of double bonds on membrane structure is the position within the acyl chain at which double bonds are found. The introduction of a double bond near the center of the acyl chain, for instance at position 9 in the formation of oleic acid from stearic acid, has the largest effect on acyl chain order. Long-chain polyunsaturates with multiple double bonds have disordering influences that are highest near the membrane interior (Hazel et al., 1992). Cold acclimation is frequently characterized by the incorporation into phospholipids of long-chain polyunsaturates such as docosahexanoic (DHA) acid, a 22-carbon acid with six double bonds. 

Polyunsaturated fatty acids are found in most lipid classes, but they are especially important as acyl chains of the phospholipids where they contribute to the particular physical and biologic functional properties of the membranes (1, 2). 

Polyunsaturated fatty acid synthesis is catalyzed by acyl-lipid-desaturases, also named front-end desaturases due to their action mechanism, which proceeds via introduction of double bonds into preformed acyl chains by oxygen and electron-donor dependent desaturation, between the carboxyl group and the pre-existing unsaturation which acts as substrate. For many microsomal desaturases, the electron donors are cytochrome b5, and a small hemoprotein that operates in numerous redox reactions in plants, involving NADH-dependent acyl-group desaturation [200]. 

Rabinovich AL, Ripatti PO (1991) On the conformational, physical properties and function of polyunsaturated Acyl Chains. Biochim Biophys Acta 1085 53-56... 

Most biophysical studies of the effects of highly polyunsaturated phospholipid acyl chains on membranes have focused on changes in acyl chain packing, sometimes referred to as fluidity, a term which has no validity at the dimensions of the bimolecular leaflets... 

In recent years, much evidence has accumulated for lateral membrane domains that differ in their relative cholesterol content (Schroeder et al., 1995), In addition, it has been proposed that high levels of sn-2 unsaturation may promote formation of microdomains, in which the saturated sn-1 chains preferentially interact with each other (Litman et al., 1991). Several studies ofcholesterol in bilayers containing high levels of polyunsaturation have reported evidence of lateral domains, which are driven by the preference of cholesterol for saturated acyl chains over polyunsaturated acyl chains (Huster et al., 1998 Mitchell Litman, 1998b Polozova Litman, 2000 Zerouga et al, 1995), The recent... 

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