Cerebrosides fatty acid components

Figure 8.15. GC separation of the TMS ethers of a ceramide fraction containing sphingosine and non-hydroxy fatty acids from brain cerebrosides [346]. A glass column (1.7 m x 3.5 mm), packed with 2.4 % OV-1 on Gas Chrom (100-120 mesh), was maintained at 300 C. Only the fatty acid component is identified. (Reproduced by kind permission of the authors and of the European Journal of Biochemistry, and redrawn from the original paper).

Hydrophobic and Hydrophilic Components of Membrane Lipids A common structural feature of membrane lipids is their amphipathic nature. For example, in phosphatidylcholine, the two fatty acid chains are hydrophobic and the phosphocholine head group is hydrophilic. For each of the following membrane lipids, name the components that serve as the hydrophobic and hydrophilic units (a) phos-phatidylethanolamine (b) sphingomyelin (c) galactosyl-cerebroside (d) ganglioside (e) cholesterol. 

Considerable proportions of cerebroside have been detected in the starfish Asterias rubens.9Ail0 It is a glucosylceramide having a-hydroxy fatty acids (from C16 to C26) and dihydroxy bases whose major components are Cl8 and C22 bases, with one, or two, double bonds. 

We initially demonstrated that brain cerebrosides, galactosyl-ceramides containing hydroxy fatty acids (HFA) and nonhydroxy fatty acids (NFA), could be completely derivatized by reaction with 10% benzoyl chloride at 60°C for 1 hour (2). After removal of excess reagents by partition between hexane and alkaline aqueous methanol, the perbenzoyl derivatives were seen to separate into two completely resolved components (HFA and NFA... 

Formation of membrane structures is also due to the hydrophobic effect. When a molecule is composed of both polar and nonpolar moieties, it is said to be amphiphilic. Since the hydrophobic effect is concerned with the tendency for nonpolar molecules or nonpolar components of molecules to associate spontaneously in aqueous solutions, there is a wide range of small molecules such as fatty acids and phospho- and glycolipids which, when dissolved in water, segregate to form membranes or micelles [146]. The same type of segregation occurs in the crystalline state, as in the structures of the long chain alkyl glycosides [147], cerebrosides,... 

The composition of milkfat is somewhat complex. Although dominated by triglycerides, which constitute some 98% of milkfat (with small amounts of diglycerides, monoglycerides, and free fatty acids), various other lipid classes are also present in measurable amounts. It is estimated that about 500 separate fatty acids have been detected in milk lipids it is probable that additional fatty acids remain to be identified. Of these, about 20 are major components the remainder are minor and occur in small or trace quantities (4, 5). The other components include phospholipids, cerebrosides, and sterols (cholesterol and cholesterol esters). Small amounts of fat-soluble vitamins (mainly A, D, and E), antioxidants (tocopherol), pigments (carotene), and flavor components (lactones, aldehydes, and ketones) are also present. 

Differences in nutritional effects between PLs and TAGs can be caused by several factors not related to their fatty acid composition, such as the presence of a phosphate group and a nitrogen base (mainly chohne) that may interact in several metabolic pathways (82). Moreover, several glycerophospholipid preparations studied can contain other components such as cholesterol, cerebrosides, sphingomyelins also depending on their source, method of isolation, and purification. These components may also affect the nutritional properties. In this chapter, the metabolic fate of constituent fatty acids of PLs and TAGs will be compared. 

Biochemistry and molecular biology of structural components. The schistosome tegument contains several phospholipids, the most abundant being phosphatidylcholine (57%), phosphatidylethanolamine (17%), sphingomyelin, lysophosphatidylcholine, phosphatidylinositol and cerebroside glycolipids (7,34). Palmitic acid and oleic acid are the most abundant fatty acids (35). These molecules are derived from the host, as schistosomes are unable to synthesize cholesterol or long-chain fatty acids de novo (36). However, schistosomes can interconvert fatty acids and cleave the polar head from some phospholipids (37). 

Hydroxyfatty adds. Fatty acids containing an OH function. In plants H. a, occur mainly as esters, e. g., in triglycerides (ricinus oil) and waxes (e.g., camauba and beeswax). In plants and animals 2-H. are components of cerebrosides. On the other hand, esters and glycosides of 3-H. [e.g. (R)-3-hydroxypalmitic acid from Rhodotorula yeasts, C gH3203, Mr 272.43, mp. 78 - 79 °C, [a]o -12.9°] are typical components of bac-... 

Lignocaric acid n-tetracosanoic acid, CH3-(CH2)22-C00H, a fatty acid M, 368.6, m.p. 84 °C. La. occurs as an esterified component of glycerides (usually less than 3%) in many seed oils, such as ground nut and rape seed oil. It is an esterified component of certain cerebrosides (e g kerasin), phospha-tides and waxes. 

---