Fatty acids chain-length determination

An example is the use of pre-gastric lipases for the production of Italian cheese types. In these cheeses the entire stomach of calves is dried and used. This results in a characteristic piquant flavour. The substrate specificity of the lipases, in terms of affinity for certain fatty acid chain lengths, determines the quality and the flavour of the final lipolyses product. 

In the second round of fatty acid synthesis, butyryl ACP condenses with malonyl ACP to form a C5-P-ketoacyl ACP. This reaction is like the one in the first round, in which acetyl ACP condenses with malonyl ACP to form a C4-P-ketoacyl ACP. Reduction, dehydration, and a second reduction convert the C5-P-ketoacyl ACP into a C5-acyl ACP, which is ready for a third round of elongation. The elongation cycles continue until Ci5-acyl ACP is formed. This intermediate is a good substrate for a thioesterase that hydrolyzes C 15-acyl ACP to yield palmitate and ACP. The thioesterase acts as a ruler to determine fatty acid chain length. The synthesis of longer-chain fatty acids is discussed in Section 22.6. 

In general, the migration order of any lipid class is determined by the overall number of double bonds in the molecule. Thus the retention of common fatty acids (chain lengths of 16-22 carbon atoms, methylene interrupted double bonds) increases with increasing number of double... 

Fig. 16.2 De novo generation of ceramide via the function of dhCerS. Recently identified dhCerSl-6 are responsible for the generation and determining the fatty-acid chain length of ceramide in the de novo pathway. For example, dhCerSl, previously known as LASSl, is responsible for generating dihydro-Cig-ceramide, whereas CersS2 and CerS4 synthesize dihydro-C22-, C24-, and C26-ceramides. In addition, dihydro-Ci2-, C14- and Ci6-ceramides are generated by CerSS and CerS6. These dihydro-ceramides are then desaturated to form ceramides by DES, dihydroceramide desaturase...

The fatty acid chain lengths synthesized by the chloroplast are primarily 16 and 18. This clearly implies that for acyl ACP of chain lengths less than 16 the predominant reaction is further elongation, and that for chain lengths of 18, elongation is rare. For 16 0 ACP,18 0 ACP, and 18 1 ACP, both transfer to the cytoplasmic compartment and acylation of glycerol-3-phosphate are distinct possibilities. The concentration of ACP in the stroma has been determined to be 8 pM [Ohlrogge eta/(12)], so only small... 

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). 

The A -stearoyl (18 0)-ACP desaturase is found in nearly all plant tissues. In addition, several other acyl-ACP desaturases have been identifi in plants, including the A -palmitoyl (16 0)-ACP desaturase of coriander seed (1), the A -16 0-ACP desaturase of Thunbergia data seed (2), and the A -myristoyl (14 0)-ACP desaturase of geranium trichomes (3). These enzymes share >70% amino acid sequence similarity. Given this high degree of structural relatedness, comparisons of the amino acid sequences of these enzymes may provide clues as to which residues dictate the fatty acid chain-length and double bond positional specificities of acyl-ACP desaturases, especially when used in conjunction with the recently determined crystal structure of the A -18 0-ACP desaturase (4). 

Mutagenesis studies have been conducted to identify amino acids associated with the substrate and regio-specificities of acyl-ACP desaturases. These studies were performed using cDNAs for a A -16 0-ACP desaturase and a A -18 0-ACP desaturase from Thunbergia alata. Based on the activities of chimeric mutants of these enzymes, a 30-amino acid domain was identified that contains determinants for fatty acid chain-length and double bond positional specificities. This domain corresponds to amino acids 178-207 of the A -18 0-ACP desaturase. When this domain was replaced in the A -lbrO-ACP desaturase with the analogous portion of the A -18 0-ACP desaturase, the resulting enzyme catalyzed both the A and A desaturation of 16 0- and 18 0-ACP. 

Finally, ion chromatography can be used to determine the a-sulfo fatty acid esters. The chromatographic column is a nonpolar poly sty rene/divinylbenzene column and the ion pair reagent is 0.005 M ammonia. In order to reduce the elution time, acetonitrile is added as a modifier with increasing concentration. This gradient technique makes it possible to separate simultaneously ester sulfonates and disalts by chain length. Determination is achieved by standards with defined chain length [107]. 

Smith, S. 1980. Mechanism of chain length determination in biosynthesis of milk fatty acids. J. Dairy Sci. 63, 337-352. 

At very high values of n the monolayer collapses (buckles). Both the cross-sectional area per molecule in the monolayer and the collapse pressure can be determined. For typical fatty acids, regardless of chain length, the area covered is only 0.2 nm2 per molecule indicating that the fatty acid chains are stacked vertically to the surface in the monolayer. The collapse... 

The physical properties of bilayers depend on their phase, which is determined by the transition temperature (Tm) of the bilayer lipid mixture. The Tm depends on the nature of the head group, the length and the degree unsaturation of the fatty acid chains and the interaction between the lipid molecules (higher Tm is obtained when hydrogen bonds are formed between phospholipid bead groups) [30]. 

Because mammals lack the enzymes to introduce double bonds at carbon atoms beyond C-9 but can increase the length of the fatty acid chain at the carboxyl end, the easiest way to determine which unsaturated fatty acid is the precursor is to note the number of carbons from the co end (CH3 end) to the nearest double bond. Thus, in (a) this number is seven carbons hence, palmitoleate is the precursor. In (b) it is six carbon atoms hence, linoleate. In (e) it is nine carbon atoms hence, oleate etc. 

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