Monoenic fatty acids, oxidation

It has been shown that toxic carbon tetrachloride can be replaced by ethyl acetate in the ruthenium-catalysed oxidation of alkenes and monoenic fatty acids. Oxidative... 

Biosynthesis of Unsaturated Fatty Acids. In the mammalian tissues, the forma-tion of monoene fatty acids is only possible. Oleic acid is derived from stearic acid, and palmitooleic acid, from palmitic acid. This synthesis is carried out in the endoplasmic reticulum of the liver cells via the monooxigenase oxidation chain. Any other unsaturated fatty acids are not produced in the human organism and must be supplied in vegetable food (plants are capable of generating polyene fatty acids). Polyene fatty acids are essential food factors for mammals. 

FIGURE 3-7 Pathways for the interconversion of brain fatty acids. Palmitic acid (16 0) is the main end product of brain fatty acid synthesis. It may then be elongated, desaturated, and/or P-oxidized to form different long chain fatty acids. The monoenes (18 1 A7, 18 1 A9, 24 1 A15) are the main unsaturated fatty acids formed de novo by A9 desaturation and chain elongation. As shown, the very long chain fatty acids are a-oxidized to form a-hydroxy and odd numbered fatty acids. The polyunsaturated fatty acids are formed mainly from exogenous dietary fatty acids, such as linoleic (18 2, n-6) and a-linoleic (18 2, n-3) acids by chain elongation and desaturation at A5 and A6, as shown. A A4 desaturase has also been proposed, but its existence has been questioned. Instead, it has been shown that unsaturation at the A4 position is effected by retroconversion i.e. A6 unsaturation in the endoplasmic reticulum, followed by one cycle of P-oxidation (-C2) in peroxisomes [11], This is illustrated in the biosynthesis of DHA (22 6, n-3) above. In severe essential fatty acid deficiency, the abnormal polyenes, such as 20 3, n-9 are also synthesized de novo to substitute for the normal polyunsaturated acids. 

In summary, it seems clear that there are significant interspecies differences in the relative and absolute rates of oxidation of different chain length fatty acids by heart muscle. The large differences in interspecies susceptibility to myocardial lipidosis would appear to be explained reasonably well by the metabolic data now available for some of these species. Obviously, more data on interspecies comparisons are badly needed. Because there are these well-documented interspecies differences, there are some obvious difficulties in extrapolating data from experimental animals to man on the interaction of 22 1 monoenes and myocardial lipidosis. 

C.,g and C20 fatty acids of the (n-9), (n-6) and (n-3) families are the most abundant trienoic fatty acids in animal tissues they elute in this order on polar stationary phases and some ECL data are contained in Table 5.3. All of the eight possible geometrical isomers of 9,12,15-octadecatrienoic acid (a-linolenic acid) have been prepared by nitrous oxide-catalysed elaidinisation [21-23,815] and by total synthesis [747]. Ackman and Hooper [21-23] were able to predict their ECL values, from data for the appropriate monoenes obtained on a WCOT column coated with Silar 5CP , by applying diethylenic... 

Allenic groups have distinctive IR and NMR spectra, and all the natural fatty acids containing this functional group exhibit a marked optical activity. The position of the group in the fatty acid chain can be determined by partial reduction and oxidation of the monoene fragments as described above [74]. 

Feeding menhaden (fish) oil at 2% of the dry matter intake of the diet also lowered milk fat concentrations. The level of CL A was increased by approximately 3.6 fold, but there was also a concurrent 4-5 fold rise in the level of vaccenic acid. Increasing the oil intake to 3% had no additional effects. The level of n-3 fatty acids in the milk was increased, mainly due to increased levels of eicosapentaenoic acid (EPA 20 5n-3), as was the level of total trans monoenes. The effects of pasteurization and oxidation on the raw milk were examined but no significant changes were observed and the CLA isomer profile was unchanged. There were no significant flavour differences found between the milk (and butter made from the milk) of cows fed 2% menhaden oil and control samples. The higher polyunsaturated fat content of the butter meant that it was softer at 4°C and 20°C, but the acid value and peroxide value of the butter were similar to those of control samples even after 3 months. A consumer evaluation of milk from cows fed a fish oil diet found no difference in acceptability compared with the control milk (Ramaswamy et al, 2001). 

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