Mass spectroscopy Fatty acids

Amides can be titrated direcdy by perchloric acid ia a nonaqueous solvent (60,61) and by potentiometric titration (62), which gives the sum of amide and amine salts. Infrared spectroscopy has been used to characterize fatty acid amides (63). Mass spectroscopy has been able to iadicate the position of the unsaturation ia unsaturated fatty amides (64). Typical specifications of some primary fatty acid amides and properties of bisamides are shown ia Tables 5 and 6. 

The second family of secreted proteins that is covalently lipidated is the family of Wnt proteins. They are also involved in numerous processes like proliferation of stem cells, specification of the neural crest, and the expanding of specific cell types. The correct regulation of this pathway is important for animal development. Willert and coworkers were the first to isolate an active Wnt molecule. Mass spectroscopy studies carried out with the isolated protein revealed that cysteine 93 is palmitoylated. Mutating this amino acid to alanine led to almost complete loss of the signaling activity. Later in 2006, a second lipidation was found on a serine in Wnt3a. " In this case, the hydroxyl side chain is acylated with palmitoleic acid. This unsaturated fatty acid seems to be crucial for the progression of the protein through the secretory pathway. The attachment of two different lipid chains may therefore serve different functions. ... 

Structural studies of glycosphingolipids involves determination of the structure of the oligosaccharide chain and of the lipid moiety. For the oligosaccharide chain, it is necessary to determine the composition, molar ratio, and sequence of the monosaccharides, their pyranose or furanose nature, and the position of glycosidic bonds and their configuration for the lipid moiety, the composition of the fatty acids and sphingosine bases must be determined. Used for these purposes are the classical, chemical methods, conventionally accepted in the chemistry of carbohydrates and lipids and based on the degradation of compounds, enzymic, and physicochemical methods, primarily mass spectrometry and n.m.r. spectroscopy. 

From the sea anemone M. senile was isolated j3-glucopyranosyl-( 1 - l)-ceramide, the structure of which was determined by mass spectrometry, H-n.m.r. spectroscopy, and chemical splitting. The major sphingosine in the cerebroside is a new base containing two double bonds and branching at one double bond, namely, 2-amino-D-eryf/jro-l,3-dihydroxy-9-methyl-( , E)-octadeca-4,8-diene. The major fatty acids are Ci6 0 and C20 o a-hydroxy acids.133... 

Hamberg and Samuelsson (111) had tried a number of polyunsaturated fatty acids earlier and concluded that the structural requirement for lipoxygenase attack was a cis,ci5-l,4-pentadiene group whose methylene carbon was at position a>-8. In other words the requirement was a distal double bond in position w-6. These authors also examined the modified products of the reaction by mass spectroscopy and found that in all cases O2 was inserted at position w-6 except for linoleic acid. In... 

Table 1 Mass spectroscopy of oxidized glucosyl ceramide that shows that the oxidation procedure allows the quantitation of a degree of unsaturation within the fatty acid moiety (taken from Reference 136)...

Surface analytical techniques such as Auger electron spectroscopy (27), X-ray photoelectron spectroscopy (28), and secondary-ion mass spectrometry (29) have been used to study LB films. Synchrotron radiation is a particularly powerful probe enabling X-ray near-edge structure and extended X-ray absorption fine structure to be measured. Angle-resolved photoemission studies (30) confirmed the existence of a one-dimensional energy band along the (CH2)jc chain in a fatty acid salt film. 

Myelin P2 was the first protein in the iLBP family whose structure was determined (Jones et al., 1988). The crystals contain three copies of the molecule in the asymmetric unit and the structure has now been refined at 2.7 A (Cowan et al., 1993). Because the crystals do not diffract beyond 2.7 A, the precision of the model is not as high as in the other studies and this factor could affect precise hydrogen bonding measurements. In an attempt to overcome this problem, the three molecules were restrained to be similar during the refinement. Only well-determined water molecules were included in the final model. No fatty acid was added to the sample, but later mass spectroscopy measurements indicated that the predominant ligand was oleic acid, which also agreed with the shape of the electron density. This density could not be accounted for by the protein model. 

The structure of anandamide was established by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. Additional data wereobtained from the GC-MS and CID measurements of the trimethylsilyl (TMS) derivative of the material. The results suggest that anandamide is an ethanolamide of a tetraenic C20 fatty acid. 

In Colombian green coffee, Boosfeld et al. (1994) and Boosfeld and Vitzthum (1995) elucidated the structure of two pairs of unsaturated aldehydes, (E,E)-2,4- and (2F,4Z)-2,4-nonadienal as well as (E,E)-2,4- and (2 , 4Z)-2,4-decadienal, probably generated via autoxidation of unsaturated fatty acids and contributing particularly to the typical green-coffee odor. The products were identified by mass spectrometry, GC-FTIR and NMR spectroscopy. The authors used particularly mild extraction techniques in order to avoid artifact formation and isomerization of the conjugated double bonds. The sensory impressions of these aldehydes at the sniffing port varied from metallic, fried, and flowery to oily notes. 

You are examining mitochondria from muscle cells of an infant who has a deficiency in one of the enzymes in the fatty acid oxidative pathway. The mitochondria consume oxygen normally when incubated with pyruvate and malate, "with succinate, or with palmitoyl CoA (in the presence of carnitine), but the rate of oxygen utilization is decreased when the mitochondria are incubated with linoleoyl CoA in the presence of carnitine. Blood levels of carnitine in the patient are low, while the levels of an unusual acylcami-tine derivative are present in blood and urine. Analysis of this acylcamitine species using mass spectroscopy reveals that it is trans-A, cis-A decadienoyl (C10 2)-acylcamitine. The infant suffers from hypotonia (lack of muscle tone) and slow weight gain. 

Isotopically labelled fatty acids and the lipids derived from them are used in studies of reaction mechanism (e.g. hydrogenation) and of lipid biosynthesis and metabolism. Compounds containing radioactive isotopes ( H, are studied by liquid-scintillation counting or radio gas chromatography. Non-radio-active labels are studied by mass spectrometry or by NMR spectroscopy. 

Composition of oil/fat. To study the composition of oil/fat it is essential to test the purity of an oil/ fat for adulteration, accidentally or voluntarily. The specific fatty acid in fat can be determined by GC by preparing methyl esters with sodium methoxide. Mass spectrometry coupled to GC (GC-MS) is the most powerful tool for identification of fatty acids separated by GC. Free fatty acids in oil (index of rancidity) can be determined by titration against standard alkali. Infrared (IR) spectroscopy, Raman spectroscopy, and ultraviolet (UV) spectroscopy (200—400 nm) are used to detect isomers (trans and cis) of unsaturated fatty acids and conjugated double bonds. It is important to study saponification value (depict fatty acid chain length), iodine value (give the degree of unsaturation), and hydroxyl value (free fatty acids present in fats). 

See also Lipids Fatty Acids Polar Lipids Determination in Biological Fluids. Liquid Chromatography Overview. Mass Spectrometry Overview. Nuciear Magnetic Resonance Spectroscopy Overview. Thin-Layer Chromatography Overview. 

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