A-D-Glucosides

This enzyme [EC 3.2.1.98] removes successive maltohex-aose residues from the nonreducing chain ends of 1,4-a-D-glucosidic linkages in amylaceous polysaccharides. 

B cyclodextrin glycosyl-transferase Ca2+ formation (and hydrolysis) of 1,4-a-D-glucoside bonds... 

A number of starch-converting enzymes belong to a single family termed the a-amylase family or family 13 hydrolases. This group of enzymes shares common characteristics such as an eight-stranded a/p barrel structure, the ability to hydrolyze 1,4-a-D-glucosidic linkages of attached polysaccharides in a-conformation, and conserved amino acid residues in the active sites of the enzymes (van der Maarel et al. 2002). 

At high concentrations of G3 and G4, condensation reactions were observed with the formation of G6 and G8, respectively, which were then hydrolyzed at their specific bonds to change the product distribution observed for G3 and G4 under dilute conditions. Condensation reactions occurred via formation of nonproductive complexes with G3 and G4 that occur with the subsites to the left of the catalytic groups. Thus, porcine pancreatic a-amylase does not hydrolyze the (1 4)-a-D-glucosidic bonds randomly. 

Synthesis of the 1,4-a-D-glucosidic bond in starch is catalyzed by starch synthase (E.C. 2.4.1.21 ADP-glucose 1,4-a-D-glucan 4-a-glucosyltransferase reaction 2) and was first reported by Leloir (13,14). Similar reactions are seen for glycogen synthesis in bacteria and cyanobacteria (15), and the enzyme is termed glycogen synthase (also E.C. 2.4.1.21). 

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... 

At the present time, it would be premature to assign a purely degradative function to P-enzyme, and, in the later discussion, it will be assumed that both P-enzyme and starch-UDPglucosyl transferase are concerned with the synthesis of (1—>4)-a-D-glucosidic linkages in plant starches. Alternative metabolic pathways are not uncommon in Nature. 

O = a-D-glucopyranosyl residue, = (1 6)-a-D-glucosidic linkage — = (1 4)-a-D-glucosidic linkage... 

This enzyme catalyzes the hydrolysis of 1,4-a-D-glucosidic bonds in polysaccharides (mechanism, 2.4.2.5), effecting successive removals of maltose units from the nonreducing end. Hydrolysis is linked to a Walden inversion at C-1, giving rise to 3-maltose. This inversion, which can be detected polarimetrically, represents a definite characteristic of an exoglycanase. 

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