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Any lipid containing the long-chain amino alcohol sphingosine (structure 1 ) or a variation of it, such as dihydrosphingosine, phytosphingosine (structure 2 ),or dehydrophytosphingosine. Sphingosine itself is synthesized by condensing a long-chain fatty acid with the amino acid serine.
Sphingosine is converted into a variety of derivatives to form the family of sphingolipids. The simplest form is a ceramide which contains a sphingosine and a fatty acid residue joined by an amide linkage. Ceramide is the basic building block of practically all of the naturally occurring sphingolipids. It can be further modified by the addition of a phosphorylcholine at the primary alcohol group to form sphingomyelin, a ubiquitous phospholipid in the plasma membranes of virtually all cells. Modification of a ceramide by addition of one or more sugars at the primary alcohol group converts it to a glycosphingolipid, which occurs widely in both the plant and animal kingdoms. See Glycoside, Lipid
Sphingolipids participate in diverse cellular functions. A number of inheritable diseases that can cause severe mental retardation and early death occur as the result of a deficiency in one or more of the degradative enzymes, resulting in the accumulation of a particular sphingolipid in tissues. These diseases are collectively called sphingolipidoses and include Niemann-Pick disease, Gaucher disease, Krabbe disease, metachromatic leukodystrophy, and several forms of gangliosidoses, such as Tay-Sachs disease. Functionally, glycosphingolipids are known to serve as important cell-surface molecules for mediating cell-to-cell recognition, interaction, and adhesion. They also serve as receptors for a variety of bacterial and viral toxins. Many glycosphingolipids can modulate immune responses as well as the function of hormones and growth factors by transmitting signals from the exterior to the interior of the cell. A number of glycolipids are also found to participate in a variety of immunological disorders by serving as autoantigens. Other sphingolipids and their metabolites may serve as second messengers in several signaling pathways that are important to cell survival or programmed cell death (apoptosis). See Autoimmunity
a complex lipid whose chemical composition includes the unsaturated amino alcohol sphingosine and the homologues or analogues of sphingosine. In all natural sphingolipids, the amino group of the sphingosine base is joined through an amide linkage to one of the higher fatty acids or hydroxy acids, which differ from one another in the length of the carbon chain and the degree of unsaturation.
Sphingolipids are divided into two main groups. The first group, the sphingophospholipids, contains residues of phosphoric acid and choline (sphingomyelins) or of phosphoric acid and inositol glycoside (phytosphingolipids). The second group, the sphingoglycolipids, contains monosaccharides, usually galactose, or oligosaccharides (cerebrosides); this group may also contain both oligosaccharides and residues of sialic acids (gangliosides).
Sphingolipids are found in the membranes of animal and plant cells. They are the main constituent of the myelin sheath of medullated nerves and of the lipids occurring in the brain. They are almost nonexistent in fat deposits. The sphingomyelins are the most widespread and constitute 20 percent of all lipids occurring in the brain. These sphingolipids consist mainly of saturated (lignoceric, stearic) acids and unsaturated acids, such as nervonic acid, having only one double bond.
REFERENCESZhukova, I. G., and G. P. Smirnova. “Glikolipidy.” In Uspekhi biologicheskoi khimii, vol. 9. Moscow, 1968.
Lehninger, A. Biokhimiia. Moscow, 1974. (Translated from English.)
Michalec, C. Biochemistry of Sphingolipids. Prague, 1967.
N. S. KOBRINA