Glucosidic link

They are highly specific in their reactions, e.g., maltose attacks the a glucosidic link (which occurs in maltose), but is without action on the 3-glucosidic links. 

Other attempts make use of the better CNS penetration of kynurenine which is converted enzymatically within the brain to kynurenic acid by kynurenine aminotransferase (Hokari et al., 1996) or the design of pro-drugs which enter the CNS more easily and are hydrolyzed within the brain e g. glucosidic-linked 7-chlorokynurenic acid (Bonina et al., 2000). 

The fibrous tissue in the cell walls of plants contains the polysaccharide cellulose, which consists of long chains of glucose units, each of which is connected by a /3-glucoside link to the C4 hydroxyl of another glucose as in the... 

Animals also store glucose in the form of starchlike substances called glycogens. These substances resemble amylopectin more than amylose, in that they are branched chains of glucose units with a-1,4- and a-l,6-glucoside links. 

Aromatic cytokinins are found in poplar,379-381 anise,382 tomato,383 Cocos nucifera m and Arabidopsis,381 In addition to BA, aromatic cytokinins are found as ortho-topolins, wc/ -topolins, hydroxylated BAs, ortho-meth-oxytopolins, and rwfto-methoxytopolins (Figure 1 1).380,381 Other derivatives have been isolated as N3-, N7-, and /VP-glucosides and A P-alanine on the adenine ring,385 and nucleosides and a glucoside linked to the ribosyl moiety.386 In spite of the several reports of their occurrence, it is not clear whether the aromatic species are common in plants. 

Structures such as CA6, CA7, and CAS have a doughnut shape and are able to host small molecules inside their cavity. Similar to amylose, the glucose units in the CAs are linked by a(l 4) bonds that adopt a Ci chair conformation. They may be considered as rigid building blocks giving fairly limited conformational freedom of the macrocycle in rotation of the C6-06 groups and limited rotational movements about the glucosidic link Cl(n)-04(n - 1)-C4... 

Now as the limit dextrins are stable toward the amylases, it seems sound to assume that they are built according to another scheme than are those parts of the starch which 3ueld maltose. In order to explain the incomplete saccharification and the formation of the limit dextrins, the author has assumed - that, although the starch molecules are built substantially according to the maltose scheme, there are at certain intervals anomalies of one kind or other which constitute hindrances to the enzyme action. Since in most cases 70 to 80% of maltose is formed from starch, it must be concluded that the normal action of the amylases is the opening of 1,4-a-D-glucosidic links. When the constitution of the chain differs in some way from that of maltose, the enzyme cannot attach itself to the anomalous part of the chain and no hydrolysis occurs. The author assumed that when, for instance, /5-amylase acts on starch, the... 

D-Glucose is found in a combined form in which its hemiacetal group has reacted with a hydroxyl on another glucose or another carbohydrate to form an acetal or glucosidic link-... 

Glycogen, stored in the livers and cells of animals, is the main carbohydrate resource for animals. The molecule is built up of a large number of monosaccharide units by glucoside links. It is insoluble in water and gives a pink color upon reaction with iodine. It is broken down in the digestive system to give glucose and maltose. 

It is now believed that the transition from cellulose I to cellulose II results in rotation of the D-glucose residues about the glucosidic link. The hydroxyl groups are then no longer all completely free to form inter-molecular hydrogen bonds, the hydroxyl group at C-3 forming an intra-... 

The discovery, shortly thereafter, of the enzyme pullulanase from the bacterium Aerobacter aerogenes helped considerably in further structural analysis of the polysaccharide. Hydrolysis of pullulan by diis enzyme showed that essentially no products containing (l->6)-ff-i>-giucosidic linkages were formed, the preponderant product being maltotriose. It was thus clear that the enzyme hydrolyzes (l->6)-a-D-glucosidic link-... 

Use has been made of the relationship between the optical rotation of D-glucans in water and cuprammonium hydroxide solution and that of the methyl mono-O-methyl-D-glucoside which is methylated on the same hydroxyl group as that involved in the glucosidic link of the glucan 34). See Table I. 

If the structure of amylopectin involves l,6 -a-glucosidic links at branch points and the action of amylase is to hydrolyze only l,4 -a-glucosidic links, then a portion of the final products of the enzymatic hydrolysis of amylopectin should be the di-... 

Kobayashi may be identical with this debranching R enzyme. In addition to these amylases acting on the 1,6 -a-glucosidic links of amylopectin there also exist amylo-1,6-glucosidases which hydrolyze the same bonds in limit dextrins of branched polysaccharides treated with jS-amylase. An amylo-1,6-glucosidase occurs in yeast and in barley malt. It is evident that crude diastase preparations may contain varying quantities of the enzymes involved in the scission of l,6 -a-glucosidic links. For this reason the purest enzymes available should be used for the determination of the end products of amylase activity. 

Muscle also contains an amylo-1,6-glucosidase which hydrolyzes the l,6 -a-glucoside links of the limit dextrin obtained from phosphorylase action on glycogen or amylopectin. The products of the reaction are glucose and a dextrin which can further be partially phosphorolyzed by the phosphorylase. 

Chitinase. The organic skeletal substance of crustaceans, insects, and fungi is composed of chitin, a chain polymer of N-acetylglucosamine (N-acetyl-2-amino-2-desoxy-D-glucose) residues connected through l,4 -i0-glucosidic links. Chitin is usually associated with protein. 

The synthesis of l,6 -a-glucosidic links in glycogen and starch is due to transglucosidation between two 1,4 chains where a 1,4 bond in one chain is transferred to make a 1,6 bond to the other chain. 

The claim of Bemfeld and Meut m dian - that they isolated an enzyme, isophosphorylase, capable of synthesizing 1,6-glucosidic link-... 

---