Very-long-chain fatty acids composition

Based on our initial assessment of the relatively broad acyl specificity of yeast LPAT, and our interest in modifying the very long-chain fatty acid (VLCFA) content of Brassicaceae seed oils (4), we expressed the SLCl-1 gene in the model oilseed Arabidopsis thaliana, and in a high erucic acid B. napus cultivar. It will be shown that the yeast SLCl-1 gene can be used to change the content and composition of plant seed oils, via increased seed LPAT activity. 

Fatty acyl-CoA synthetase. Cytosolic processing of fatty acid and lipid formation is a highly integrated process. An active acyl-CoA pool exists and is dependent upon a supply of fatty acid from the plastid. The composition of this pool can be analyzed by capillary electrophoresis (MacKenzie and Taylor, 1990). Formation of acyl-CoAs involves fatty acyl-CoA synthetase (EC 6.2.1.3) and appears to occur on the inner face of the plastidic envelope. While a broad specificity for fatty acids exists in various oilseeds, a preference is shown for medium-chain fatty acids in Cuphea and for very-long-chain fatty acids in Crambe (Battey and... 

Suh, M., Wier bicki, A A., Lien, E., and Clandinin, M. T (1996) Relatioreship between dietary supply of long-chain fatty acids and membrane composition of long- and very-long-chain essential fatty acids in developing rat photoreceptors, l.ipicis 31, 61-64. 

LAP also appears to play several critical functions. LAP plays an important role in fatty acid absorption. LAP is able to dephosphor-ylate the phosphorylated fatty acid translocase FAT/CD36, which is thought to play a role in facilitating the transport of long-chain fatty acids into cells. In addition, Uke TNAP, LAP is able to dephos-phorylate LPS. The locahzation of the active site of LAP into the gut lumen allows LAP to protect gut barrier function and determine the composition of the gut microbiota. These functions of LAP, Uke those of TNAP, may have very important therapeutic appUcations. 

Each membrane in a cell has its distinct set of proteins and lipids. The most common membrane lipids are phospholipids. Phospholipids are diglycerides. Two of the three hydroxyls of glycerol are linked to long-chain fatty acids by ester bonds. The third position is occupied by phosphate. A number of different polar substituents are linked to the phosphate by anhydride bonds. The phospholipid composition of the mitochondrial inner membrane is virtually the same in plant mitochondria as in animal mitochondria and resembles that in the plasma membrane of some bacteria. The lipids in chloroplast membranes are very distinctive. The phospholipid content is unusually low and about 80% of the membrane lipids in thylakoids are diglycerides that have one or two galactose (a six-... 

The major differences between the lipids of bovine and human milk are in fatty acid composition and triacylglycerol structure. Bovine milk contains substantial quantities of C4 o-Ci0 o, about 2% Cis 2 and almost no other long-chain polyunsaturated fatty acids. The fatty acid composition is not altered by ordinary changes in diet. Human milk contains very little C4 o-C10 o, 10-14%i (w/w of fat) Ci8 2, and small quantities of other polyunsaturates. The triacylglycerol structure differs, with much of the sn-2 position in human milk lipids occupied by C16 0 and the sn-2 position of bovine milk-fat occupied by C4 o-Ci0 o-... 

Fixed oils and fats are naturally occurring products, usually of plant origin, that are used extensively in pharmaceutical formulation. They are very susceptible to oxidative decomposition (a process called rancidity) and special precautions must be taken to control their stability and prevent their decomposition. Compounds of this type exist as complex mixtures of structurally similar oils, the composition of which can vary from year to year depending on factors such as climate, time of harvest, etc. Chemically, fixed oils and fats are esters of the alcohol glycerol (propane-1,2,3-triol) with three molecules of long-chain carboxylic acids, called fatty acids, which may all be the same or may differ depending on the oil (Figure 8.15). 

Suh M, Wierzbicki AA, Clandinin MT. Dietary fat alters membrane composition in rod outer segments in normal and diabetic rats impact on content of very-long-chain (C>24) polyenoic fatty acids. Biochim Biophys Acta 1994 1214 54-62. 

The fatty acid compositions of phosphatidylcholines and sphingomyelins from several mammals are shown in Table 3.221. In contrast to tri-acylglycerols, the fatty acids of these phospholipids are mainly long and very long chain. Palmitic, stearic, oleic and, sometimes, linoleic acids are major components of the phosphatidylcholine fraction. In contrast, sphingomyelin has much smaller amounts of unsaturated components. Palmitic, stearic, arachidic, behenic and lignoceric acids are major components. In sheep milk sphingomyelin, tricosanoic acid is a major constituent while in the other species shown nervonic acid is the major unsaturated fatty acid (Table 3.221). 

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