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A large important class of sugar derivatives in which the sugar is combined with a nonsugar. In their cyclic forms, monosaccharides (simple sugars) possess one carbon (C) atom (the anomeric carbon) that is bonded to two oxygen (O) atoms; one oxygen atom forms a part of the ring, whereas the other is outside the ring (exocyclic) and is part of a hydroxyl (OH) group. If the oxygen atom of the anomeric hydroxyl group becomes bonded to a carbon atom, other than that of a carbonyl (C ═ O) group, the resulting compound is a glycoside. A glycoside thus consists of two parts (see illustration): the sugar (glycosyl) unit, which provides the anomeric carbon, and the moiety (the aglycon), which is the source of the exocyclic oxygen and carbon atoms of the glycosidic linkage. Such compounds frequently are referred to as O-glycosides to distinguish them from analogs having a sulfur (thio- or S-glycosides), nitrogen (amino- or N-glycosides), or carbon (anomalously called C-glycosides) as the exocyclic atom on the anomeric carbon. See Monosaccharide

The formation of glycosides is the principal manner in which monosaccharides are incorporated into more complex molecules. For example, lactose (illus. b), the most abundant disaccharide in mammalian milk, has a glycosidic bond involving the anomeric carbon of d -galactose and the C-4 hydroxyl of d -glucose. The anomeric carbon atom can exist in either of two stereoisomeric configurations, a fact which is of immense importance to the chemistry and biochemistry of glycosides. For example, the principal structural difference between cellulose and amylose is that cellulose is β-glycosidically linked whereas amylose is α-linked. Humans are able to digest amylose but are unable to utilize cellulose for food. See Cellulose, Lactose

Structural formulas of two glycosidesenlarge picture
Structural formulas of two glycosides

A very large number of glycosides exist in nature, many of which possess important biological functions. In many of these biologically important compounds the carbohydrate portion is essential for cell recognition, the terminal sugar units being able to interact with specific receptor sites on the cell surface.

One class of naturally occurring glycosides is called the cardiac glycosides because they exhibit the ability to strengthen the contraction of heart muscles. These cardiotonic agents are found in both plants and animals and contain complex aglycons, which are responsible for most of the drug action; however, the glycoside may modify the biological activity. The best-known cardiac glycosides come from digitalis and include the drug digoxin.

Glycosidic units frequently are found in antibiotics. For example, the important drug erythromycin A possesses two glycosidically linked sugar units. See Antibiotic

Perhaps the most ubiquitous group of glycosides in nature is the glycoproteins; in many of them carbohydrates are linked to a protein by O-glycosidic bonds. These glycoproteins include many enzymes, hormones, such antiviral compounds as interleukin-2, and the so-called antifreeze glycoproteins found in the sera of fish from very cold marine environments. See Amino acids, Carbohydrate, Enzyme, Glycoprotein, Hormone

Glycolipids are a very large class of natural glycosides having a lipid aglycon. These complex glycosides are present in the cell membranes of microbes, plants, and animals. See Glycolipid, Lipid

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A compound that yields on hydrolysis a sugar (glucose, galactose) and an aglycon; many of the glycosides are therapeutically valuable.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Farmers and consumers in areas that depend upon cassava should be warned about cyanide poisoning caused by eating improperly processed or wild-cultivar cassava, and instructed to strictly adhere to the established processing methods to degrade cyanogenic glycosides.
In all the fermented bamboo shoot, it showed a degradation of cyanogenic glycoside content as it is volatile, the loss of cyanogen content during fermentation processes like peeling, slicing, cutting, repeated washing.
The presence of cyanogenic glycosides was not found in any of the analyzed species, but in some species the presence of saponins was recorded (Table 2).
Alkaloids (+) (-) Anthraquinones (-) (-) Cyanogenic glycosides (-) (-) Flavonoids (++) (+++) Steroids (+++) (+++) Tannins (-) (++) Legend: (+) presence, (++) abundant, (+++) very abundant and (-) absence
The cytotoxic plants include (1) the toxalbumins, the toxin (ricin) of which one, the castor bean (Ricinus communis), has been weaponized; (2) the mitotic inhibitors, many of which are highly effective as cancer chemotherapeutics; and (3) the cyanogenic glycosides contained in the kernels of several fruits, including apples, apricots, cherries, peaches, and plums (Table 1).
Combined with an increase in cyanogenic glycosides, this has major implications for the types of crops that can be grown in the future if CO2 levels continue to rise.
Internal organ poisons include the alkaloids and cardiac and cyanogenic glycosides. Also producing toxicity in the internal organs are plants containing oxalates, resins, and phytotoxins.
Comparative Processing of Cyanogenic Glycosides and a Novel Cyanide Inhibitory Enzyme in Heliconius Butterflies (Lepidoptera: Nymphalidae: Heliconiinae).
Cyanide and cyanogenic glycosides. In: Herbivores: Their Interactions with Secondary Plant Metabolites (Rosenthal GA, Berenbaum MR, eds).