Enzymes branched polysaccharides

Type III Limit dextrinosis, Forbes or Corl s disease Absence of debranching enzyme Accumulation of a characteristic branched polysaccharide. 

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. 

The specificity of potato Q-enzyme h been examined in some detail. With amylose as donor substrate, the DP must exceed 40 n-glucose residues for rapid transglucosylation to occur with a branched polysaccharide as donor, the outer chains must exceed 14 n-glucose residues. Since linear chains of this length are not attacked by Q-enzyme, there are evidently multiple sites for the binding of Q-enz3une and its substrate. 

The monomer-up approach opens up the possibility of enzymatically grafting branched polysaccharides from functionalized substrates in order to make hybrid materials bearing a highly branched amylose part. Following the same route we are currently synthesizing hybrid materials bearing (hyper)branched polysaccharide structures as shown in Figure 9.11 with the described tandem reaction of two enzymes. 

I, 6-branching points in substrates like amylopectin. Isoamylase has higher affinity to large branched polysaccharides. The enzyme is very rare among microorganisms and has been detected in Pseudomonas amyloderamosa and Cytophaga sp.[29> 30). 

R-Enzyme was first isolated from broad beans and potatoes by Peat and coworkers. Purification was difficult in view of the relatively small amounts present and the large number of contaminating enzymes, particularly a maltodextrinyl transferase (D-enzyme), branching (Q-) enzyme, and alpha-amylase. However, a procedure was developed that gave preparations suflBciently pure to permit routine use of this enzyme during some ten years for debranching of amylaceous polysaccharides. ... 

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. 

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