Of glycolipids

Oligosaccharide and polysaccharide structures occur not only in free form but often as parts of glycopeptides or glycoproteins [11] or of glycolipids [21]. It can be cumbersome to designate their structures by using the recommendations of 2-Carb-37. The use of three-letter symbols for monosaccharide residues is therefore recommended. With appropriate locants and anomeric descriptors, long sequences can thus be adequately described in abbreviated form. 

IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of glycolipids, in preparation. 

The presence and biological importance of oligosaccharide structures, usually as components of glycolipids and glycoproteins, in bacterial capsular and cell-wall polysaccharides, in mammalian cell membranes, in cytoplasm, and in extracellular fluids, are now well documented. They are important constituents in... 

D-Galactose Hydrolysis of lactose. Can be changed to glucose in the liver and metabolized. Synthesized in the mammary gland to make the lactose of milk. A constituent of glycolipids and glycoproteins. Failure to metabolize leads to galactosemia and cataract. 

Ganglio-series GIcNAcpi -4Galp1 -4Glcpi -1 Cer ganglio-series of glycolipids. 

Spiegel, S., Skutelsky, E., Bayer, E.A., and Wilchek, M. (1982) A novel approach for the topographical localization of glycolipids on the cell surface. Biochim. Biophys. Acta 687, 27-34. 

Lipids are transported between membranes. As indicated above, lipids are often biosynthesized in one intracellular membrane and must be transported to other intracellular compartments for membrane biogenesis. Because lipids are insoluble in water, special mechanisms must exist for the inter- and intracellular transport of membrane lipids. Vesicular trafficking, cytoplasmic transfer-exchange proteins and direct transfer across membrane contacts can transport lipids from one membrane to another. The best understood of such mechanisms is vesicular transport, wherein the lipid molecules are sorted into membrane vesicles that bud out from the donor membrane and travel to and then fuse with the recipient membrane. The well characterized transport of plasma cholesterol into cells via receptor-mediated endocytosis is a useful model of this type of lipid transport. [9, 20]. A brain specific transporter for cholesterol has been identified (see Chapter 5). It is believed that transport of cholesterol from the endoplasmic reticulum to other membranes and of glycolipids from the Golgi bodies to the plasma membrane is mediated by similar mechanisms. The transport of phosphoglycerides is less clearly understood. Recent evidence suggests that net phospholipid movement between subcellular membranes may occur via specialized zones of apposition, as characterized for transfer of PtdSer between mitochondria and the endoplasmic reticulum [21]. 

Figure 5.14 Freeze-etch electron micrograph of glycolipid nanotubes from 24 1 nonhydroxy galactocerebrosides (21) cryofixed from room temperature in water. Bar = 250 nm. Reprinted from Ref. 64 with permission of the Biophysical Society.

Many solvent combinations have been described for two-dimensional separation and, in general, if an alkaline or neutral solvent is chosen for the first dimension then the second solvent should be acidic. Also it may be useful for one solvent to contain acetone, which will enhance the movement of glycolipids relative to the phosphoglycerides. Acetic acid should not be used in the first solvent, because it is difficult to remove completely and affects the quality of the separation in the second dimension. Difficulties are also encountered in the removal of butanol, which interferes with the charring process often used for the location of the spots. 

Mudd, J. B.. T. T. McManus, A. Ongun, and T. E. McCullough. Inhibition of glycolipid biosynthesis in chloroplasts by ozone and sulfhydryl reagents. Plant Physiol. 48 335-339, 1971. 

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