Unsaturated fatty acids trans

Offer, N.W., Marsden, M., Dixon, J., Speake, B.K., and Thacker, F.E. 1999. Effect of dietary fat supplements on levels of n-3 poly-unsaturated fatty acids, trans acids and conjugated linoleic acid in bovine milk. Anim. Sci. 69, 613-625. 

FIGURE 24.23 )3-Oxidation of unsaturated fatty acids. In the case of oleoyl-CoA, three /3-oxidation cycles produce three molecules of acetyl-CoA and leave m-AAdodecenoyl-CoA. Rearrangement of enoyl-CoA isomerase gives the tran.s-A species, which then proceeds normally through the /3-oxidation pathway. 

The specific behaviour of unsaturated fatty acids under oxidation is determined by the position and the number of double bonds in the fatty acid molecule. The stepwise oxidation of an unsaturated acid to the position of a double bond in it proceeds in a manner similar to that of saturated acid oxidation. If the double bond retains the same configuration (trans-configuration) and position (A2,3) as those of the enoyl-CoA, which is produced during the oxidation of saturated fatty acids, the subsequent oxidation proceeds via conventional route. Otherwise, the oxidation reaction proceeds with the involvement of an accessory enzyme, A3,4-CiS-A2,3jrans-enoyl-CoA isomerase this facilitates the translocation of the double bond to an appropriate position and alters the double-bond configuration from cis to trans. 

If a fatty acid already has a double bond in it, the scheme by which the fatty acid is oxidized depends on where the double bond ends up after several of the C-2 fragments have been removed by normal p oxidation. With a double bond already present, the enzyme that catalyzes the first step (insertion of the double bond at C-2) gets confused when there is already a double bond at C-2 or at C-3. The fact that the double bonds in unsaturated fatty acids are invariably cis also complicates life since the double bond introduced at C-2 by the desaturating enzyme of p oxidation is a trans double bond. 

If the double bond is on an odd carbon, (3 oxidation removes 2-car-bon fragments until it gets to the structure with a 3-cis double bond [R-CH=CH-CH2-C(=0)-SCoA]. A new double bond can t be placed between C-2 and C-3 because there s already a double bond at C-3. In this situation, the activity of an isomerase simply moves the double bond from C-3 to C-2 and at the same time makes sure that the configuration is trans. From this point on, the metabolism is just like normal (3 oxidation (hydration, oxidation, cleavage). If you re counting ATPs, these unsaturated fatty acids produce 2 fewer ATPs for each double bond since there is no FADH2 produced by putting in the double bond (see Fig. 13-6). 

It should be noted that Reaction (4) is not a one-stage process.) Both free radical N02 and highly reactive peroxynitrite are the initiators of lipid peroxidation although the elementary stages of initiation by these compounds are not fully understood. (Crow et al. [45] suggested that trans-ONOO is protonated into trans peroxynitrous acid, which is isomerized into the unstable cis form. The latter is easily decomposed to form hydroxyl radical.) Another possible mechanism of prooxidant activity of nitric oxide is the modification of unsaturated fatty acids and lipids through the formation of active nitrated lipid derivatives. 

Tran. -isomers are much rarer than cis-isomers. Many different positional isomers of monoenoic acids may be present in a single, natural lipid and this is not a comprehensive list. Palmitoleic and oleic acids are quantitatively the commonest unsaturated fatty acids in most organisms. Odd-chain monoenoic acids are minor components of animal lipids but are more significant in some fish and bacterial lipids. 

Recently, we reported that the rhodium/BIPHEPHOS-catalyzed hydroformylation of trans-4-octene (Scheme 6) provides an interesting approach for the synthesis of n-nonanal [23]. In this context trans-4-octene can also be seen as a model substance for hydroformylation of internally unsaturated fatty acid esters. This could open up access to the use of renewable resources for the synthesis of valuable n-aldehydes. 

Trans-unsaturated fatty acid from its CIS- and trans-isomeric mixture Na-ZSM-5 [182]... 

Jacobs, P.A., Maes, P., Paulussen, S.J., Tielen, M., Van Steenkiste, D.F.E., and Van Looveren, L.K. (2001) Elimination of trans-unsaturated fatty acid compounds by selective adsorption with zeolites. U.S. Patent 6,229,032. 

Note that the term trans fats refers to fats containing trans fatty acids. At a couple of points earlier, 1 emphasized that aU the common unsaturated fatty acids possess cis carbon-carbon double bonds. It is true that some common foods—beef and dairy products—contain very small amounts of trans fatty acids but it is also true that the vast preponderance of dietary trans fats come from processed foods. Here is one example of a normal cis fatty acid—oleic acid—and its trans isomer ... 

Trans fats fats containing unsaturated fatty acids that have the trans geometry at their carbon-carbon double bonds. 

The unsaturated fatty acids exhibit geometric isomerism, i.e. there are cis and trans forms (Figure 11.10). The chemical basis for isomerism is discussed in Chapter 3. (Appendix 3.1). 

Ruminant bacteria produce some trans -unsaturated fatty acids when long-chain fatty acids are synthesised in the bacteria. These are absorbed by the host so that trans-unsaturated fatty acids can be found in adipose tissue and muscle of ruminants. 

In lipid metabolism, ds-trans isomerism is particularly important. For example, double bonds in natural fatty acids (see p.48) usually have a as configuration. By contrast, unsaturated intermediates of p oxidation have a trans configuration. This makes the breakdown of unsaturated fatty acids more complicated (see p. 166). Light-induced cis-trans isomerization of retinal is of central importance in the visual cycle (see p.358). 

Unsaturated fatty acids usually contain a cis double bond at position 9 or 12—e.g., linoleic acid (18 2 9,12). As with saturated fatty acids, degradation in this case occurs via p-oxida-tion until the C-9-ds double bond is reached. Since enoyl-CoA hydratase only accepts substrates with trans double bonds, the corresponding enoyl-CoA is converted by an iso-merase from the ds-A, cis- A isomer into the trans-A, cis-A isomer [1]. Degradation by p-oxidation can now continue until a shortened trans-A, ds-A derivative occurs in the next cycle. This cannot be isomerized in the same way as before, and instead is reduced in an NADPH-dependent way to the trans-A compound [2]. After rearrangement by enoyl-CoA isomerase [1 ], degradation can finally be completed via normal p-oxidation. 

Hunter, J. E., Zhang, J., and Kris-Etherton, P. M. (2009). Cardiovascular disease risk of dietary stearic acid compared with trans, other saturated, and unsaturated fatty acids A systematic review. Am.. Clin. Nutr. 91(1), 46-63. 

Unsaturated fatty acids may occur as cis or trans isomers trans isomers, which have higher melting points than the corresponding cis isomers, are considered to be nutritionally undesirable. Bovine milk fat contains a low level (5%) of trans fatty acids in comparison with chemically hydrogenated (hardened) vegetable oils, in which the value may be 50% due to non-stereospecific hydrogenation. 

Oxidation of unsaturated fatty acids The oxidation of unsatu rated fatty acids provides less energy than that of saturated fatly I acids because they are less highly reduced and, therefore, tom I reducing equivalents can be produced from these structured Oxidation of monounsaturated fatty acids, such as 18 1(9) (deb acid) requires one additional enzyme, 3,2-enoyl CoA isomeras which converts the 3-cis derivative obtained after three rounds (3-oxidation to the 2-trans derivative that can serve as a substra for the hydratase. Oxidation of polyunsaturated fatty acids, sue ... 

Triacylglycerols are quantitatively the most important class of dietary fats. Their biologic properties are determined by the chemical nature of the constituent fatty acids, in particular, the presence or absence of double bonds, the number and location of the double bonds, and the cis-trans configuration of the unsaturated fatty acids. 

Trans fatty acids Trans fatty acids (Figure 27.13) are chemically classified as unsaturated fatty acids, but behave more like saturated fatty acids in the body, that is, they elevate serum LDL (but not HDL), and they increase the risk of CHD. Trans fatty acids do not occur naturally in plants and only occur in small amounts in animals. However, trans fatty acids are formed during the hydrogenation of liquid vegetable oils, for example, in the manufacture of margarine. 

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