Amylosucrase, polysaccharide synthesis

In addition to the synthesis of polysaccharides, the transglucosylation activity of GH family 13 amylosucrase from N. polysaccharea has been employed to modify amylo-polysaccharides, underlying the interest of this enzyme for the design of novel thickening agents, resistant starches, and original carbohydrate-based dendritic nanoparticles [73, 74]. 

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. 

Amylosucrase 173) from Neisseria perflava utilizes sucrose for the synthesis of polysaccharides with properties intermediate between those of glycogen and amylopectin 174). Apparently, there are two enzymes responsible for this synthesis one enzyme converts sucrose into an amylose-type polysaccharide and the other enzyme, which is of the Q-enzyme type, breaks the straight chains to produce highly branched molecules. The resultant branched polysaccharides have about 12 D-glucose units for each nonreducing end unit. 

When cultures or enzyme preparations of N. perfiava are allowed to act on a-D-glucose-l-phosphate, some amylopolysaccharide is produced, indicating the presence of a phosphorylase. However, the amylosucrase can be distinguished from the bacterial phosphorylase by its stability to heat and by the fact that the synthesis of the polysaccharide from sucrose is not suppressed in high concentration of inorganic phosphate. The synthetic reaction proceeds without a noticeable lag period, suggesting that primer material, if needed, is present in the preparations. Although there is no direct evidence for this, the fact that the formation of polysaccharide is completely inhibited in the presence of traces of salivary amylase indicates that a primer may be required. 

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