Glycoproteins carbohydrate components

Some biomolecules contain carbohydrate components. Nucleotides, the building block molecules of the nucleic acids, contain either of the sugars ribose or deoxyribose. Certain proteins and lipids also contain carbohydrate. Glycoproteins and glycolipids occur on the external surface of cell membranes in multicellular organisms, where they play critical roles in the interactions between cells. 

The amount of bound water (studied by H n.m.r. spectroscopy) and the extended molecular conformation appear to be responsible for the anti-freeze properties of a glycoprotein from the Antarctic fish Dissostichus mawsoni. Chemical modification has shown that the carbohydrate moiety of the glycoprotein component of the (Na + K )ATPase in membrane preparations of the salt glands from dog fish does not contribute to the catalytic activity of the enzyme. One of two glycoproteins extracted from squids (Sepia officinalis) resembles collagen. ... 

FIGURE 8.18 Dolichol phosphate is an initiation point for the synthesis of carbohydrate polymers in animals. The analogous alcohol in bacterial systems, undecaprenol, also known as bactoprenol, consists of 11 isoprene units. Undecaprenyl phosphate delivers sugars from the cytoplasm for the synthesis of cell wall components such as peptidoglycans, lipopolysaccharides, and glycoproteins. Polyprenyl compounds also serve as the side chains of vitamin K, the ubiquinones, plastoquinones, and tocopherols (such as vitamin E). 

The carbohydrate components of a glycoprotein range from 1% to more than 85% of its weight and may be simple or very complex in structure. 

Human IL-2 is a single-chain polypeptide containing 133 amino acids. It is a glycoprotein, the carbohydrate component being attached via an O-linked glycosidic bond to threonine... 

By means of gel electrophoresis on cross-linked, hydrolyzed starch,99 with simultaneous checking for proteins, lipids, and pectinesterase activity, it was found, however, that the product isolated after the separation on CM-Sephadex C-50 constitutes but one of five multiple forms of tomato pectinesterase, and is the one present in preponderant proportion98 (see Fig. 4). The accompanying lipid and sugar components were separated from this pectinesterase form in the course of the purification procedure. After analysis of the hydro-lyzate of the final product for fatty acids, as well as for carbohydrate components, it was possible to exclude the possibility of a lipoprotein,30 as well as glycoprotein,100 character of this form of tomato pectinesterase. 

The components of the plant cell wall (8-21) are the middle lamella (intercellular substance), the primary wall, and the secondary wall. The middle lamella is the pectic layer between cells and holds adjoining cells together as do membrane carbohydrates. The primary wall is thin (1-3 pm) and flexible containing cellulose, hemicelluloses, pectins, and glycoproteins. This wall provides mechanical strength, maintains cell shape,... 

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