Acyl chains saturated

One of the commonest relationships noted in adaptation of membranes to temperature is a decrease in acyl chain saturation during acclimation to reduced temperature. Hazel (1988) has reviewed changes in molecular species composition during acclimation in bacteria, plants, and animals. As a broad generalization, a decrease in acclimation temperature of 20° C is accompanied by a decrease of approximately 19% in the percentage of fully saturated acyl... 

Figure 5 Two representative iysophosphoiipid chemicai structures showing stereochemistry. Molecules can exist with variable acyl chain saturation. Common names, chemical formulas, and molecular weights (g/mol) are given.

SCDs are a family of microsomal Fe-based metalloenzymes. They act on long-chain saturated acyl CoAs and introduce a ds-double bond at the C-9 or C-10 position. For example, SCDs convert stearic acid into oleic acid, and palmitic acid into palmitoleic acid. Monounsaturated FAs constitute a major component of TGs, cholesteryl esters, and phospholipids. The reaction requires molecular 02 and NADH and generates H20 in the process [3,4]. 

Many conformations were sampled by the usual MC procedure. The result is of course that there is no preferred orientation of the molecule. Each conformation can, however, be characterised by an instantaneous main axis this is the average direction of the chain. Then this axis is defined as a director . This director is used to subsequently determine the orientational order parameter along the chain. The order is obviously low at the chain ends, and relatively high in the middle of the chain. It was found that the order profile going from the centre of the molecules towards the tails fell off very similarly to corresponding chains (with half the chain length) in the bilayer membrane. As an example, we reproduce here the results for saturated acyl chains, in Figure 10. The conclusion is that the order of the chains found for acyl tails in the bilayer is dominated by intramolecular interactions. The intermolecular interactions due to the presence of other chains that are densely packed around such a chain,... 

From the density profiles one cannot really judge the effect of the double bonds the density profiles for membranes of saturated lipids are very similar to those of unsaturated ones. Therefore it is necessary to consider some of the conformational characteristics of the tails. It is possible to compute the order parameter profile for both the saturated and the unsaturated chains. The order parameter profile for the saturated chain closely follows the results presented in Figure 17 for DMPC membranes for both the SCF and the MD predictions. The order parameter profiles for the unsaturated chain closely follows the MC predictions, as discussed in Figure 9. A pronounced dip is found near the cis double bond. For this reason, we choose here to present complementary data about the conformational properties of the acyl chains. 

From the modelling results for bilayers composed of unsaturated lipids one can begin to speculate about the various roles unsaturated lipids play in biomembranes. One very well-known effect is that unsaturated bonds suppress the gel-to-liquid phase transition temperature. Unsaturated lipids also modulate the lateral mobility of molecules in the membrane matrix. The results discussed above suggest that in biomembranes the average interpenetration depth of lipid tails into opposite monolayers can be tuned by using unsaturated lipids. Rabinovich and co-workers have shown that the end-to-end distance of multiple unsaturated acyl chains was significantly less sensitive to the temperature than that of saturated acyls. They suggested from this that unsaturated... 

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.

Recently, the effect of the lipid composition on the permeability in PAMPA was investigated [129], By varying the phosphate head group and the saturation degree of the acyl chain, differences in transport were observed for a set of five model compounds, which was due to changes in membrane fluidity and ion pairing [129],... 

The cleavage of /7-nitrophenyl alkanoates (222 n = 1-8) at high pH is modestly catalysed by micelles formed from cetyltrimethylammonium bromide (CTAB) in aqueous solution. Rate constants exhibit saturation behaviour with respect to [CTAB], consistent with substrate binding in the micelles. The strength of substrate binding and transition state binding to the micelles increases monotonically with the acyl chain length, and with exactly the same sensitivity. As a result, the extent of acceleration... 

Long-chain fatty acyl-CoA synthetase [EC 6.2.1.3] catalyzes the reaction of ATP with a long-chain carboxylic acid and coenzyme A to produce an acyl-CoA, AMP, and pyrophosphate. While utilizing a wide range of long-chain saturated and unsaturated fatty acids as substrates, enzymes from different tissues vary in their specificity. 

Figure 8-4. 3-Oxidation of palmitate. Oxidation of an even-numbered, saturated fatty acid involves repetitive cleavage at the (1 carbon of the acyl chain. Removal of two-carbon units occurs in a cycle of four steps initiated by one of the acyl CoA dehydrogenases. Acetyl CoA is produced at each cycle until all that remains of the acyl CoA is acetyl CoA itself.

Some animal tissues and some unicellular organisms are rich in ether lipids, in which one of the two acyl chains is attached to glycerol in ether, rather than ester, linkage. The ether-linked chain may be saturated, as in the alkyl ether lipids, or may contain a double bond between C-l and C-2, as in plasmalogens (Fig. 10-9). Vertebrate heart tissue is uniquely enriched in ether lipids about half of the heart phospholipids are plasmalogens. The membranes of halophilic bacteria, ciliated protists, and certain invertebrates also contain high proportions of... 

Length of a Fatty Acid Molecule The carbon carbon bond distance for single-bonded carbons such as those in a saturated fatty acyl chain is about 1.5 A. Estimate the length of a single molecule of palmitate in its fully extended form. If two molecules of palmitate were placed end to end, how would their total length compare with the thickness of the lipid bilayer in a biological membrane ... 

We now take a closer look at the first stage of fatty acid oxidation, beginning with the simple case of a saturated fatty acyl chain with an even number of carbons, then turning to the slightly more complicated cases of unsaturated and odd-number chains. We also consider the regulation of fatty acid oxidation, the j8-oxidative processes as they occur in organelles other than mitochondria, and, finally, two less-general modes of fatty acid catabolism, a oxidation and [Pg.637]

The long carbon chains of fatty acids are assembled in a repeating four-step sequence (Fig. 21-2). A saturated acyl group produced by this set of reactions becomes the substrate for subsequent condensation with an activated malonyl group. With each passage through the cycle, the fatty acyl chain is extended by two carbons. When the chain length reaches 16 carbons, the product... 

FIGURE 21-3 The overall process of palmitate synthesis. The fatty acyl chain grows by two-carbon units donated by activated malonate, with loss of C02 at each step. The initial acetyl group is shaded yellow, C-l and C-2 of malonate are shaded pink, and the carbon released as C02 is shaded green. After each two-carbon addition, reductions convert the growing chain to a saturated fatty acid of four, then six, then eight carbons, and so on. The final product is palmitate (16 0). 

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