Triacylglycerol chirality

The three acyl residues of a fat molecule may differ in terms of their chain length and the number of double bonds they contain. This results in a large number of possible combinations of individual fat molecules. When extracted from biological materials, fats always represent mixtures of very similar compounds, which differ in their fatty acid residues. A chiral center can arise at the middle C atom (sn -C-2) of a triacylglycerol if the two external fatty acids are different. The monoacylglycerols and diacylglycerols shown here are also chiral compounds. Nutritional fats contain palmitic, stearic, oleic acid, and linoleic acid particularly often. Unsaturated fatty acids are usually found at the central C atom of glycerol. 

FIGURE 10-2 Glycerol and a triacylglycerol. The mixed triacylglycerol shown here has three different fatty acids attached to the glycerol backbone. When glycerol has two different fatty acids at C-1 and C-3, the C-2 is a chiral center (p. 76). 

Triacylglycerol lipases (EC 3.1.1.3) are attracting renewed attention since they were demonstrated to be active in organic solvents and to be suitable catalysts in industrial important reactions, such as the synthesis of flavors, emulsifiers, and chiral compounds, and the transesterifi cation of tow-value fats to triacylglycerols of high commercial value. Fbngi are a particularly valuable source of lipases because the enzymes produced by the majority of them are extracellular and readily separable from the mycelia after fermentation. The recent availability of... 

In the final stages of this fat synthesis, fatty acyl coenzyme A molecnles react with a-glycero-phosphoric acid to give phosphatidic acid, which is a chiral compound by virtue of the asymmetric carbon C (11.98). Phosphatidic acid can now be hydrolysed to yield a 1,2 diacylglycerol which will react with another molecule of fatty acyl coenzyme A to give a triacylglycerol according to (11.99). 

Itabashi, Y., Kuksis, A., Marai, L. and Takagi, T. (1990) Chiral phase high performance liquid chromatographic resolution of diacylglycerol moieties of natural triacylglycerols on R-(+)-l-(1-naphthylethylamine). J. Lipid Res., 31, 1711-17. 

A chiral center exists in a triacylglycerol when the acyl residues in positions 1 and 3 are different ... 

Iwasaki, Y, Yasui, M, Ishikawa, T, Irimescu, R, Hata, K and Yamane, T (2001) Optical resolution of asymmetric triacylglycerols by chiral-phase high-performance liquid chromatography. J. Chromatogr., 905, 111-118. 

Duque, M. Graupner, M. Stuetz, H. Wicher, I. Zechner, R. Paltauf, F. Hermetter, A. New fluorogenic triacylglycerol analogs as substrates for the determination and chiral discrimination of Upase activities. J. Lipid Res. 1996,37,868-876. 

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