Anteiso-branched fatty acids

Abbreviations a-BFAs anteiso-branched fatty acids AGP acyl carrier protein BHLH active soluble domain of SREBP CNS central nervous system DSD delta 5 desaturase D6D delta 6 desaturase ER endoplasmic reticulum Hik histidine kinase HUFA highly unsaturated fatty acid LXR liver X receptor MUFA monounsaturated fatty add NF-Y nuclear factor Y PLs phospholipids PP peroxisome proliferator PPAR PP-activated receptor PPRE PP response element PUFA polyunsaturated fatty acid PUFA-BP PUFA binding protein PUFA-RE PUFA response element RXR retinoid X receptor SCAP SREBP cleavage-activating protein SCD steraroyl CoA desaturase SFA saturated fatty acid SRE sterol response... 

Many substituted, ie, branched, fatty acids, particularly methacryUc, 2-ethylhexanoic, and ricinoleic acids, are commercially significant. Several substituted fatty acids exist naturally (Table 5). Fatty acids with a methyl group in the penultimate position are called iso acids, and those with a methyl group in the antepenultimate position are called anteiso acids (1) (see Carboxylic acids, branched-CHAIN acids). However, the term iso is often used in a broader sense to mean branched or mixtures of branched-chain industrial acids. 

Branched fatty acids of the anteiso series have a branch here and a 5-carbon "starter piece" derived from isoleucine... 

Branched-chain fatty acids (BrFAs) (iso- and anteiso) are believed to be primarily derived from sulfate-reducing bacteria (Perry et al., 1979 Cranwell, 1982 Canuel et al., 1995 table 9.5). However, it should be noted that BrFAs are not present in all sulfate-reducing bacteria or other heterotrophic bacteria (Kaneda, 1991 Kohring et al., 1994). The iso- and antesio- designation represents a branched fatty acid with the methyl group at the a>-l position and the methyl group at the a>-2 position, respectively. The odd number (C45, C17, branched and normal) are believed to be derived from phospholipids, components of bacterial cell membranes (Kaneda, 1991). Even-numbered iso-branched fatty acids (e.g., C12—Cig) are also found in algal sources (Schnitzer and Khan, 1972). 

Branched fatty acids iso- and anteiso fatty acids believed to be primarily derived from sulfate-reducing bacteria the iso- and antesio designation represents a branched fatty acid with the methyl group at the w-1 position and the methyl group at the co-2 position, respectively. 

These branched acids can be source-specific and they are rarely unsaturated. They are formed by the incorporation of branched amino acids into the biosynthetic pathway, yielding iso and anteiso acids, as noted in Section 5.1.3. Iso and anteiso saturated fatty acids are found in fungi, molluscs and phytoplankton, but they are generally in higher levels in bacteria and are often observed in the C13—C17 range (Harwood Russell 1984).The C15 isomers (Fig. 5.1) are usually particularly abundant in bacteria and the ratio (iso + anteiso)/normal derived from C15 components can be used as an indication of relative bacterial contributions (Parkes Taylor 1983). Similarly, the (08 isomers of /. >- 5 1 and iso-17 1 are bacterial markers (Perry et al. 1979), and iso-17 1(07 is characteristically a major fatty acid in the sulphate-reducing bacteria Desulfovibrio desulfuricans (Taylor Parkes 1983). 

It is relatively rare to find significant quantities of both odd chain length and branched chain fatty acids in biological systems. However such compounds have been Isolated and identified from the epicuticular wax from Brussels sprout leaves, with anteiso-C j and anteiso-C making up 36% of the total saturated fatty acid fraction (13). Similarly Radunz has isolated and identified iso and anteiso mono methyl branched fatty acids in phospholipids, contained in yellow-white leaves and petals of the plastome mutants "Prasinizans" of Antirrhinum majus and "Xanthr of Nicotiana tabacum M4T In addition small amounts of odd chain length fatty acids and alcohols have been found in the surface waxes of Zea mays husks (15). 

In most bacterial species C15 fatty acids are present in trace amounts, so their elevated levels (2-3 times higher than any other fatty acid) in propionibacteria can serve as a diagnostic marker. However, this marker should be taken with caution, since the levels of free fatty acids in bacteria depend on media composition, age of culture and the level of vitamin B12 in the cells. Addition of isoleucine to die medium increases the synthesis of anteiso-C s acid by propionibacteria. In the presence of L-leucine they produce more / o-Ci5 acid by decreasing anteiso-C s acid (Moss et al., 1969). In the cells of young active cultures usually the level of straight-chain mono-unsaturated acids (Cie i, Cis i) is higher. The content of mono-unsaturated fatty acids is higher than the branched-chain fatty acids in cultures deficient in vitamin B12. With the cell free extract of C simplex it was shown that vitamin B12 deficit leads to a decrease in the activity of transmethylase system and in the rate of the transformation of mono-unsaturated acids to CHs-branched fatty acids (Fujii and Fukui, 1969). A distinct fatty acid composition was found (Kusano et al., 1997) in P. cyclohexanicum. The major fatty acid was o-cyclohexyl undecanoic acid, while iso- and anteiso-C s, C16, and Cn fatty acids were also present, but in a small amount. 

Branched-chain fatty acids occur widely in nature, but tend to be present as minor components except in bacteria, where they appear to replace unsaturated fatty acids functionaiiy. Usually, the branch consists of a single methyl group, either on the penultimate (/so) or antepenultimate (anteiso) carbon atoms (Figure 2.2). In the biosynthesis of these fatty acids, the primer molecules for chain-elongation by the fatty acid synthetase are 2-methylpropanoic and 2-methylbutanoic acids, respectively. Methyl branches can be found in other positions of the chain (on even-numbered carbon atoms), if methylmalonyl-coenzyme A rather than malonyl-coenzyme A is used in for chain extension this can occur in bacteria and in animal tissues, especially those of ruminant animals, where polymethyl-branched fatty acids even can be synthesised [275]. 

Mono-methyl branched fatty acids of the iso- and anteiso types with chain lengths of 12 to 22 carbon atoms were found in yellow-white leaves and petals of the plastome mutants "Prasinizans" of Antirrhinum majus and "Xanthi"ot Nicotiana tabacum. These branched chain fatty acids are preponderantly esterified in the sn-2 position of the glycerol backbone of the membrane phospholipids namely phosphatidylcholine, phosphatidyletha-nolamine and phosphatidylinositol. The phospholipids appear to contain 16-24 per cent iso- and anteiso fatty acids, 19-47 per cent unsaturated and 38-63 per cent saturated fatty acids. The methyl-branched chain fatty acids seem to take over the function of the unsaturated fatty acids. 

In a previous publication we had reported that yellow-white leaves of the plastome mutant "Prasinizans" of Antirrhinum majus contained methyl-branched fatty acids (1). They make up for 6-8 per cent of the total fatty acids. The methyl-branched fatty acids were isolated via urea adducts and characterized by means of comparative gas chromatography with authentic fatty acids (2,3) by IR-spectroscopy, NMR-spectroscopy and by means of the measured optical activity as mono- and methyl-branched fatty acids of the iso- and anteiso-types (1). 

Branched fatty acids, known as iso-acids and anteiso-acids, occur normally in small quantities in fats. Their synthesis begins with the amino-acids valine and isoleucine (Figure 3.12). This has been demonstrated with radio-labelled isotopes, by radio-active monitoring and with stable isotopes by C nuclear magnetic resonance spectroscopy or mass spectrometry. Both isobutyric acid and 2-methylbutyric acid are common defensive compounds among insects. Note that a chiral centre is introduced in 2-methylbutyric acid and anteiso acids. 

Bacillus sp. Salted ponds Bulgaria Series of saturated branched fatty acids, iso and anteiso, from Cn to C19 phenylalcanoic acids — Carballeira eta/., 2001... 

Fig. 21.15. Partial gas chromatogram of extracted lipids. Peaks Ci4 0 to Ci8 o> saturated straight fatty chain acids (FA) with 14 to 18 carbon atoms C45br and Ci7 r, iso- and anteiso- branched-chain fatty acids Ci8 i FA, mono-unsatu-rated CigtoOH-FA, hydroxylated form derived by bacterial hydration of the original oleic acid. (Reprinted/redrawn from Nature, 432, 35-36, Copyright 2004, Nature Publishing Group, with permission.)...

Massart-Leen et al. (1981) analyzed bovine milk fat and goat milk fat for branched chain fatty acids. They did not find the same diversity of fatty acids in bovine as in goat milk fat and as previously reported. The authors suggested that the difference—the absence of branched chain acids other than iso and anteiso in bovine milk fat—could be caused by the relative inefficiency of the incorporations of methylmalonic acid into the biosynthetic pathway. 

Their study agrees with the Myher et al. (130) estimation in the identification of TGs with odd-carbon-number fatty acids (CN = 15 and 17), either branched or linear. However, they have been able to differentiate between iso and anteiso isomers not only in the GLC analysis of fatty acids but also in TG estimation. Tridecanoic and nonadecanoic acids were identified by GLC but were not included in TG estimation due to their low amounts in whole milk fat content. 

Linear capsiacinoids with a C9/C12 chain are only trace constituents of capsicum oleoresin, which mainly contains branched capsaicinoids. The acyl moiety of these compounds is produced by the branched chain fatty acids pathway (Scheme 4.1) [30[. Depending on the nature of the amino acid that acts as the acyl starter precursor, different capsaicinoids are formed. Thus, capsaicinoids of the iso series such as CPS and homocapsaicin I are derived from valine and leucine via isobutyrylCoA and isovalerylCoA, respectively, while those from the anteiso series such as homocapsaicin II originate from isoleucine via 2-methylbutyrylCoA (Scheme 4.1) [31[. The polymethylene moiety of norcapsaicin has one less carbon than capsaicin. The... 

The basic fish oil (27) also included a generous amount of saturated fatty acids. As can be seen from Figure 5 and Table 1, the saturated fatty acids are dominated by the 16 0 (palmitic acid), usually accompanied by about half as much or less of 14 0 (myristic acid) and much less of 18 0 (stearic acid). Usually the saturated fatty acid totals are at least 20%, especially as the odd chain (15 0, 17 0) and methyl-branched (iso, anteiso, pristanic, phytanic) fatty acids (compare Figure 4) are sam-rated and will total around 2-3%. An unsaturated peak that is often observed is 17 ln-8, which is roughly equal to 17 0. The details of these peaks are discussed in other publications, but those researchers attempting modern open-tubular gas chromatography analyses should be aware of their presence and influence on peak identification and quantitation. As can be seen from Figure 6, there is an... 

Recently, a unique anteiso methyl-branched saturated fatty acid of 21 carbons, 18-methyl eicosanoic acid or 18-MEA, was identified in the outermost portion of the epicuticle, which is part of the CMC [104,106-110], 18-MEA is the predominant fatty acid in the epicuticle. It makes up approximately 40% of the surface lipid layer of wool and human hair [106,107,109], In addition to 18-MEA, other fatty acids have been isolated in smaller amounts from the epicuticle including... 

Other bacteria use different systems to regulate fluidity. For example, gram-positive bacteria alter the ratio of iso- to anteiso-branched-chain fatty acids in response to temperature [20]. However, the biochemical mechanisms that govern this universal response to environmental temperature are largely unknown in most bacterial species. 

Two major types of BCFAs occur in nature iso series and anteiso series [2]. Anteiso-15 0, having methyl branching at antepenultimate positions (anteiso), showed cytotoxicity comparable to that of iso-15 0 [7]. Thus, the Djq of both iso-15 0 and anteiso-15 0 were lower than those of corresponding straight-chain fatty acids. 

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