Fatty acid activation and

Figure 10-4 Reactions of fatty acid activation and of breakdown by (S oxidation.

We have already encountered an acyl adenylate intermediate in fatty acid activation (Section 22.2.2). The major difference between these reactions is that the acceptor of the acyl group is CoA in fatty acid activation and tRNA in amino acid activation. The energetics of these biosyntheses are very similar both are made irreversible by the hydrolysis of pyrophosphate. 

Fatty Acid Activation and Transport into Mitochondria (Diagram)... 

Table 23.1. Chain-Length Specificity of Fatty Acid Activation and Oxidation Enzymes...

The enzymes in the pathways of fatty acid activation and p-oxidation (the synthetases, the carnitine acyltransferases, and the dehydrogenases of p-oxidation) are somewhat specific for the length of the fatty acid carbon chain. The chain length specificity is divided into enzymes for long-chain fatty acids (C20 to approximately C12), medium-chain (approximately C12 to C4), and short-chain (C4-C2). The major lipids oxidized in the liver as fuels are the long-chain fatty acids (palmitic, stearic, and oleic acids), because these are the lipids that are synthesized in the liver, are the major lipids ingested from meat or dairy sources, and are the major form of fatty acids present in adipose tissue triacylglycerols. The liver, as well as many other tissues, uses fatty acids as fuels when the concentration of the fatty acid-albumin complex is increased in the blood. 

Some drugs impair mitochondrial function through a combination of mechanisms. A good example is valproic acid, which inhibits mitochondrial fatty acid oxidation by sequestering coenzyme A (a cofactor necessary for fatty acid activation and... 

Hence, activation precedes hydroxylation. Although 3-MBFA can be activated at different cellular sites— mitochoniia, peroxisomes and endoplasmic reticuliun —only the peroxisomal activity seems to supply a precursor for the hydroxylation reaction. Whether the acyl-CoA synthetase acting on phytanic acid is the same as the one activating palmitic acid and pristanic acid is a matter of controversy. Anyway, the requirement for an activation step e q)lains the inhibition of a-oxidation by fenoprofen, an inhibitor of long chain fatty acid activation, and by different fatty acids (unpublished data), presumably due to competitive inhibition or by depletion of the available CoA. 

Aktiplast T Combination of zinc salts of unsaturated fatty acids, activator and process aid... 

Thus, all the processes of fatty acid activation and oxidation are efficiently concentrated as components of the glyoxysomal system converting lipid to carbohydrate precursors, as described by Beevers (this volume. Chapter 4). 

The short chain activating enzyme, acetyl-CoA synthetase, showed a similar developmental increment. Palmitylcarnitine transferase activity of developing rat liver and heart homogenates increased from negligible levels at the time of birth to adult levels by thirty days of age (Fig. 4). These changes were associated with a large increase in the overall rate of fatty acid oxidation in the rat (Fig. 5). Thus, both fatty acid activation and acylcarnitine transferase activity appear to be of considerable importance for the development of fatty acid oxidation in the rat. Augenfeldt... 

Oxidation of 8 molecules of acetyl-CoA each producing 12 molecules of ATP Less 2 ATP equivalents expended during the initial fatty acid activation and conversion of ATP to AMP... 

Fatty-acid soaps have some inherent characteristics which make them more acceptable as a means of reducing compound viscosity than do chemical peptizers. Because of their fatty-acid soap base they could eliminate or reduce the need for added fatty acid activators, and considerably reduce the stickiness of low-viscosity natural rubber masterbatches. They can be used in a number of applications where conventional chemical peptizers could cause contamination problems, e.g. in the food industry. They must, however, be used in considerably higher dosages than chemical peptizers. 

When the diet contains a small, but normally adequate, amount of linoleic acid which is swamped by enormous amounts of other fatty acids in the diet (e.g. oleic acid or isomeric fatty acids, section 8.15.3). In this situation, the fatty acids in excess compete successfully with linoleic acid for the A6-desaturase and generate a series of polyunsaturated fatty acids that have no essential fatty acid activity and cannot substitute for the linoleic acid family. The effect of this competition is illustrated in Figure... 

Xanthates and dithiophosphates dominate sulfide flotation usage, though several other collectors including more recently developed ones are gaining acceptance rapidly (43). As of this writing, this is an active area of research. Many of the sulfide collectors were first used ia the mbber iadustry as vulcanizers (16). Fatty acids, amines, and sulfonates dominate the nonsulfide flotation usage. The fatty acids are by-products from natural plant or animal fat sources (see Fats and fatty oils). Similarly petroleum sulfonates are by-products of the wood (qv) pulp (qv) iadustry, and amines are generally fatty amines derived from fatty acids. 

A study of the effect of stearic acid and 2iac oxide on a sulfonamide-accelerated, sulfiir-cured natural mbber compound dramatically showed the need for both 2iac and fatty acid activators (Fig. 7) (21). 

FIGURE 25.16 Regulation of fatty acid synthesis and fatty acid oxidation are conpled as shown. Malonyl-CoA, produced during fatty acid synthesis, inhibits the uptake of fatty acylcarnitine (and thus fatty acid oxidation) by mitochondria. When fatty acyl CoA levels rise, fatty acid synthesis is inhibited and fatty acid oxidation activity increases. Rising citrate levels (which reflect an abundance of acetyl-CoA) similarly signal the initiation of fatty acid synthesis. 

For long-chain alcohol esters it is interesting to see that the interfacial tension between a 0.01 wt % aqueous solution and octane or xylene has a minimum for ester sulfonates with a total 22 carbon atoms in the fatty acid chain and the ester chain [60]. The balance in length between the two chains has only a poor effect. Thus, a-sulfonated fatty acid esters with a total number of 22-26 carbon atoms in the molecule have excellent interfacial activities. To attain the same magnitude in the interfacial tension between linear alkylbenzenesulfonate (LAS) solution and octane, the required concentration of LAS is 0.1 wt %. This is 10 times the concentration needed for a-sulfonated fatty acid esters [60]. 

Insulin stimulates lipogenesis by several other mechanisms as well as by increasing acetyl-CoA carboxylase activity. It increases the transport of glucose into the cell (eg, in adipose tissue), increasing the availability of both pyruvate for fatty acid synthesis and glycerol 3-phosphate for esterification of the newly formed fatty acids, and also converts the inactive form of pyruvate dehydrogenase to the active form in adipose tissue but not in liver. Insulin also—by its ability to depress the level of intracellular cAMP—inhibits lipolysis in adipose tissue and thereby reduces the concentration of... 

McPhail, L.C., Clayton, C.L. and Snyderman, R (1984). A potential messenger role for unsaturated fatty acids activation of Ca -dependent protein kinase. Science 224, 622-625. 

E. Baath, A. Frostegard, and H. Fritze, Soil bacterial bioma.ss, activity, phospholipid fatty acid pattern, and pH tolerance in an area polluted with alkaline dust deposition, Appl. Environ. Microbiol. 5S 4026 (1992). 

Thiazolidinediones are known to increase insulin sensitivity by stimulating peroxisome proliferator-activated receptor gamma (PPAR-y). Stimulation of PPAR-y results in a number of intracellular and extracellular changes, including an increased number of insulin receptors, increased insulin receptor sensitivity, decreased plasma fatty acid levels, and an increase in a host of intracellular signaling proteins that enhance glucose uptake. 

Fatty Acids and Lipids Although several fatty acids, esters and alcohols are known to be toxic to plant growth, their role in allelopathy is not fully investigated (3). Dihydroxystearic acid (3, 49) is the classic example known to exhibit allelopathic activity. 

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