glycoside

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Glycoside

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

glycoside

[′glī·kə‚sīd]
(biochemistry)
A compound that yields on hydrolysis a sugar (glucose, galactose) and an aglycon; many of the glycosides are therapeutically valuable.
References in periodicals archive ?
Bu nedenle daha fazla hastanin dahil edildigi butun genomun taranabilecegi yeni bir calisma planlanmasinin, pozitif veriler elde edilebildigi taktirde, transgenik hayvan orneklerinde "knock-out" veya "knock-down" yontemleri ile genin canlidaki islevlerinin ayrintili olarak incelenmesinin, hastaligin genetik yonunun daha iyi degerlendirilebilmesi acisindan yararli olacagi inancindayiz.
When the cool surface water sank, it pushed deep, nutrient-rich water upward, says Genin.
5, that Genin "distorts Marguerite's rather confused and linguistically awkward first letter to Francois.
We'll do just that," Genin said, referring to Eastern's plan to revamp the brew's formula to suit American's palates.
Norofibromatoz 1 hastalarinda gelisen tumorlerde genin homozigot mutasyonu saptanmistir.
HOUSTON -- COADE announced today that it will be participating with dealer Genin & Garces at the 19th World Petroleum Congress in Madrid, Spain, on June 29 - July 3, where COADE products will be featured in exhibit booth #9101, including CADWorx, the company's complete AutoCAD-based package for intelligent plant design modeling and automatic isometrics; PV Elite, for pressure vessel and heat exchanger design and pressure vessel analysis; and CAESAR II, the world's leading pipe stress analysis program.
BOUCHERVILLE, Quebec, Canada-After more than 100 years, Genin Trudeau, a leading acrylic supplier based here, will change its corporate name and brand name to Trudeau effective today.
HOUSTON -- COADE announced today that the next stops on the COADE Discovery Tour will be April 15 in Madrid, and April 16 in Bilbao, Spain, organized in conjunction with Genin & Garces, COADE's dealer covering the region.
Cedric Genin, entertainment and digital media expert, to manage the Paris office, while marketing specialist Paul Raven to head up the London location
says Remy Genin, Chief Agile Evangelist & Director of Agile Methodologies at Orange.
Genin Trudeau Tessin Designs Tettau Porcelain Tiamo US-China Glassware Inc.