Polysaccharides glycogen type

In a second class of regulatory enzymes the active and inactive forms are inter-converted by covalent modifications of their structures by enzymes. The classic example of this type of control is the use of glycogen phosphorylase from animal tissues to catalyse the breakdown of the polysaccharide glycogen yielding glucose-1-phosphate, as illustrated in Fig. 5.37. 

In contrast to the above-mentioned protozoa which synthesize glycogen-type polysaccharides, certain ciliates (for example, Cycloposthium) contain an amylopectin-type of polysaccharide, whilst the flagellate Polytomella caeca stores a typical two-component starch. ... 

For the synthesis of glycogen-type polysaccharides from a-n-glucopyran-osyl phosphate, two enzymes are required. Phosphorylases, in presence of a suitable primer, synthesize linear chains of -( —> 4)-linked n-glucose residues these are then converted into a branched polysaccharide by a branching enzyme. ... 

The conversion of sucrose into a branched polysaccharide of the amylo-pectin-glycogen type by a bacterial-enzyme system was discovered by Hehre and his coworkers. Enzyme action involves the synthesis of polymeric chains of (1— 4)-linked a-D-glucose residues by a transglucosylase named amylosucrase, followed by the action of a branching enzyme. 

Erlanderi has suggested an alternative theory, which accounts for the coexistence of a granular starch and a glycogen-type polysaccharide in sweet corn, and which is also applicable to all other plants. It is postulated that glycogen is synthesized first partial debranching then occurs, to yield amylopectin and short, linear chains of (1— 4)-linked a-D-glucose... 

VII. Synthesis of Starch-Glycogen Type Polysaccharides by Transglucosidases 260... 

VII. SYNTHESIS OF STARCH-GLYCOGEN TYPE POLYSACCHARIDES BY TRANSGLUCOSIDASES... 

Glucose molecules are bound in starch by the easily hydrolyzed a bonds. The same type of bond can also be seen in the animal reserve polysaccharide glycogen. This is in contrast to many structural polysaccharides such as chitin, cellulose and peptidoglycan, which are bound by P-bonds and are much more resistant to hydrolysis. A starch branching enzyme introduces 1,6-a glycosidic bonds between these chains, creating the branched amylopectin (Figure 5.28). 

Although a polysaccharide can be made of any type of monosaccharide units, the polysaccharides of the human diet are made only of glucose. These polysaccharides include starch, glycogen, and cellulose, which differ from one another only in how the glucose units are chained together. All polysaccharides, but especially the ones in our diet, are known as complex carbohydrates, where complex refers to the multitude of monosaccharide units linked together. 

A polymaltose prepared by Ricketts and Rowe140 reacted with pneumococcus Type XII antiserum more extensively than did a polyglucose prepared by the same authors, but both polysaccharides left behind some antibody reactive with glycogen. Neither polymer reacted with Type II antiserum. Polygalactose gave a slight precipitate with Type IV antiserum, the capsular polysaccharide of which is known to contain D-galactose. 

The enzymes used for this type of digestion in Analytical Chemistry are mainly hydrolytic enzymes, the catalytic effect of which is based on the insertion of water at a specific bond of the substrate. The hydrolytic enzymes used in analytical applications include lipases (which hydrolyse fats into long-chain fatty acids and glycerol) amylases (which hydrolyse starch and glycogen to maltose and to residual polysaccharides) and proteases (which attack the peptide bonds of proteins and peptides themselves). 

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