Exchange of fatty acids

There are at least three roles for the exchange of fatty acids (i.e. the cycle). 

To measure the activity in transesterification, equimolar amounts of triolein and tripalmitin were reacted by means of immobilized enzyme (8). The transesterification was followed by HPLC analysis of the triglycerides. One Batch Transesterification Unit is the initial exchange of fatty acids in jtcmol per min. 

Enzymatic Methods The use of enzymes to produce fatty acids and fatty acid-derived products has been a focus in both academic and industrial circles. Lipases may catalyze esterification, hydrolysis, or exchange of fatty acids in esters (115). These processes can be selected by choosing appropriate substrates and reaction conditions. Lipase-catalyzed processes have attracted attention because of the mild reaction conditions under which they occur and the selectivity displayed by these catalysts. In both respects, they differ from typical chemical reactions. As enzymatic reactions occur under mild temperature and pH conditions and at ambient pressure, they generally require less energy and are conducted in equipment of lower capital cost than many other chemical processes. Another advantage of enzymatic process is related to the selectivity of many lipases, which allows obtaining products that are difficult to produce by more conventional chemical reactions. 

Although the balance between glucose and fatty acid oxidation is described in Chap. 13, it is relevant to note here that malonyl-CoA inhibits carnitine acyl transferase I (CAT-1), the enzyme that catalyzes the exchange of fatty acids for carnitine as part of the cytosol-to-matrix fatty acid transport system. Inhibition of CAT-I occurs when acetyl-CoA carboxylase is activated by insulin. By inhibiting the uptake of fatty acids into mitochondria, malonyl CoA favors the oxidation of glucose and prevents fatty acids from being oxidized at the same time as they are being synthesized. 

A study of the exchange of fatty acids, labeled from [ C]acetate, between potato microsomes and mitochondria (Mazliak and Ben Abdelkader, 1971) showed that all types of fatty acids were transferred, the major ones being the most extensively exchanged. There was no breeikdown of fatty acids and no subsequent synthesis during the transfer, since the distribution of C radioactivity remained constant among the various fatty acids in the donor and the acceptor fractions. 

Table 3. Exchange of fatty acids from microsomes to mitochondria...

Acidolysis of fatty adds with diterpene abietic add (3-156), the main component of the so-called resin acids (see Section 8.2.14) is used, for example, to produce varnishes, where the exchange of fatty acids for phthaHc acid yields glyptals (polymers containing the ester functional group with properties of natural resins). 

Examples of such intra cellular membrane transport mechanisms include the transfer of pyruvate, the symport (exchange) mechanism of ADP and ATP and the malate-oxaloacetate shuttle, all of which operate across the mitochondrial membranes. Compartmentalization also allows the physical separation of metabolically opposed pathways. For example, in eukaryotes, the synthesis of fatty acids (anabolic) occurs in the cytosol whilst [3 oxidation (catabolic) occurs within the mitochondria. 

The brain has no significant stores of triacylglycerol, and the oxidation of fatty acids obtained from blood makes little contribution to energy production because fatty acids do not efficiently cross the blood-brain barrier. The intertissue exchanges characteristic of the absorptive period are summarized in Figure 24.8. 

Silver ion chromatography is a useful technique for separating geometrical isomers of fatty acids (as the methyl ester derivatives) for subsequent analysis by GC. On the other hand, a stable ion-exchange column loaded with silver ions has been developed for HPLC that has proved of value in the simplification of complex mixtures of fatty acids (FAs) of natural origin for subsequent identification by GC-MS and for separating molecular species of triacylglycerols (41). 

The components of biodiesel are vegetable oils composed of glycerol esters of fatty acids. In the process of transesterification, the glycerol components of the triglyceride molecules are exchanged for methanol. The products are fatty-acid methyl esters consisting of straight saturated and unsaturated hydrocarbon chains, as described under chemical processes. 

---