Branched monoenoics

Figure 7.18 Variation in microbial community structure and indicators of environmental stress within different parts of the concretion and host sediment from profile 93LD (a) community structure -TBS = terminally branched saturates, MBS = mid-branched saturates Poly = polyenoics, Total Mono = total monoenoics, BMono = branched monoenoics. Sedi-far represents the host sediment at some distance from the concretion but at the same stratigraphic level (b) indicators of nutritional stress (c) biomarkers for Desu/fobacfer<10Me16 0) and Desulfovibrio

Fatty acids of plant, animal, and microbial origin usually consist of an even number of carbon atoms in the straight chain. The number of carbon atoms of fatty adds in animals may vary from 2 to 36, whereas some microorganisms may contain 80 or more carbon atoms. Also, fatty adds of animal origin may have one to six ds double bonds, whereas those of higher plants rarely have more than three double bonds. Fatty adds also may be saturated, monounsaturated (monoenoic), or polyunsaturated (polyenoic) in nature. Some fatty acids may consist of branched chains, or they may have an oxygenated or cyclic structure. 

Hay and Morrison (1971) later presented additional data on the fatty acid composition and structure of milk phosphatidylethanolamine and -choline. Additionally, phytanic acid was found only in the 1-position of the two phospholipids. The steric hindrance presented by the four methyl branches apparently prevents acylation at the 2-position. The fairly even distribution of monoenoic acids between the two positions is altered when the trans isomers are considered, as a marked asymmetry appears with 18 1 between the 1- and 2-positions of phosphatidylethanolamine, but not of phosphatidylcholine. Biologically, the trans isomers are apparently handled the same as the equivalent saturates because the latter have almost the same distribution. There are no appreciable differences in distribution of cis or trans positional isomers between positions 1 and 2 in either phospholipid. Another structural asymmetry observed is where cis, cis nonconjugated 18 2s are located mostly in the 2-position in both phospholipids. It appears that one or more trans double bonds in the 18 2s hinders the acylation of these acids to the 2-position. 

Figure 7.14 Indicators of community structure and environmental stress in profile 93LD indicated by (a) abundance of monoenoics, (b) abundance of branched saturates, (c) the ratio of OHFA to PLFA, (d) the biomarker for Desulfobacter (10Me16 0), (e) the biomarker for Desulfovibrio (i17 1w7c), and (f) the ratio of cy19 0/18 1w7c.

Psammaplysins S (48) and T (49) also have their hydroxyl derivatives as well. Psammaplysins U-W and its hydroxyl derivatives (52-56) have monoenoic fatty acid side chain s connected with the terminal amine as an amide functionality. Psammaplysin U (52) has Ao-branched fatty acid side chain, while psammaplysins V (54) and W (55) have unbranched fatty acid side chains. Psammaplysins X (57) and Y (59) were isolated from marine sponge of the genus Suberea [29]. Psammaplysin X (57) has 4-chloro-2-methylenecyclopentane-l,3-dione at the A-terminus, while psammaplysin Y (59) has unsubstituted 2-methylenecyclopentane-l,3-dione moiety at its A-terminus (Figure 3). 

In fact a fatty acid does not have to have two or more double bonds in order to serve as a substrate for a 5-desaturase. A number of different cis and trans monoenoic acids are desaturated at position 5 (Lemarchal and Bornens, 1968 Mahfouz and Holman, 1980 Pollard eta/., 1980a). When seven different methyl branched isomers of 8,11,14-20 3 were used as substrates for desaturation with rat liver microsomes only the 13, 17, 18, and 19 methyl branched substrates were desaturated at significant rates. The 2, 5, and 10 methyl branched isomers were virtually inactive (Do and Sprecher, 1975). It remains to be determined whether a single acyl-CoA 5-desaturase can act on such a variety of different substrates. 

Butterfat is the most complex natural fat on the basis of its fatty acid (Table 3.153 Jensen etal, 1962) and triglyceride (Table 3.157) composition. There are approximately 15 major acids but over 500 acids have been characterized. The composition of butter-fat is further complicated because it contains numerous isomers of the monoenoic, dienoic and branched chain acids (Table 3.154) (Jensen et ai, 1962 Hay and Morrison, 1970 Deman and Deman, 1983 Van der Wen and de Jong, 1967). Such complex mixtures are probably best characterized by combinations of HPLC, capillary GLC and mass spectrometry. The higher-molecular-weight fatty acids have been characterized in some detail (Table 3.154) (Iverson et ai, 1965). 

Wax esters in their most abundant form consist of fatty acids esterified to long-chain alcohols with similar aliphatic chains to the acids. They are found in animal, plant and microbial tissues and have a variety of functions, such as acting as energy stores, waterproofing and even echo-location. The fatty acids may be straight-chain saturated or monoenoic with up to 30 carbons, but branched-chain and a- and co-hydroxy acids are present on occasion similar features are found in the alcohol moieties. 

Polar phases are used almost universally for fatty acid analysis, although the inherent resolution of WCOT columns is such that some remarkable separations can be achieved even with non-polar silicone phases, which are more stable at elevated temperatures. Such columns are easier to manufacture than are polar ones. For example, the separation of a hydrogenated fish oil is a horrendous problem for any stationary phase, yet a published chromatogram obtained with a 44 m column coated with the non-polar OV-73 (175,000 theoretical plates) is probably as good as any in which polar phases have been used [870]. A set of retention data has been published for cod liver oil fatty acids on a 50 m fused silica column coated with SP-2100 a large number of isomeric branched-chain monoenoic and polyenoic components were clearly resolved [298]. A short column of this type was used for the analysis of plasma fatty acids [925]. 

The difficulties involved in the analysis of complex mixtures of branched-chain fatty acids are perhaps best illustrated by some selected examples of actual analyses, and the reader may find illuminating those studies of such components in human milk [238], Vernix caseosa (mono-, di- and trimethylbranched) [668], ruminant tissues [232,853], avian uropygial gland secretions (reviews) [423,425], the bacteria Streptomyces R61 and Acfinomadura R39 [136] and the bacterium Desulfovibrio desulfuiicans iso- and anfe/so-methylbranched and monoenoic) [117]. 

---