Maltotriose structure

Benzylated 1,6-anhydroglucose has been used as donor in the construction of maltose and maltotriose structures with high a-selectivity (O Scheme 52) [112], Interestingly, 1,6-anhy-drodisaccharides were found to be unreactive as donors with 4-thiosaccharide acceptors, and could consequently be used as alternative acceptors. 

B-chains until they are acted on by R-enzyme, when maltose or malto-triose will be produced from the residual A-chain, and linear dextrins from the B-chains. The amount of maltose or maltotriose liberated on treating the /3-limit dextrin with R-enzyme will be a measure of the number of A-chains in the molecule, and from these data, the ratio of A B chains in the molecule can be calculated.220 Peat concluded that multiple branching is an intrinsic part of the amylopectin structure, as the observed yield of these sugars was greater than expected for a singly-branched structure. It should be noted that glycogen has been shown by similar enzymic methods to possess a truly random structure.221... 

Figure 7.21 Determination of the structure of Bacillus amyloliquefaciens a-amylase limit dextrin, using enzymes no reaction with (3-amylase (b) reaction with pullulanase to give maltose + maltotriose (c) reaction of glucoamylase to give two tetrasaccharides, both ofwhich are eventually converted into panose + glucose. Analysis of the reactions can be made by thin layer chromatography239.

Pullulanase is an extracellular enzyme of Aerobacter aerogenes that causes essentially quantitative hydrolysis of pullulan to maltotriose. The enzyme is readily prepared in a crude form that is free from other carbohydrases, and is important in structural studies because it debranches amylopectin and glycogen. When the A. aerogenes is grown in continuous culture, the enzyme is bound to the cells, but it can be released by detergents, and purified by ion-exchange chromatography. This purified enzyme has been crystallized. ... 

Figure 1. Chemical structure ofpullulan containing maltotriose units and of dextran containing a-1,6 linked anhydroglucose units with a-1,3 branch points.

In addition to its in vivo importance, R-enzyme is extremely useful for structural analysis. For example, the release of maltose and maltotriose from amylopectin jS-dextrin by R-enzyme provides good evidence of multiple branching, since the yield (12.8%) is near to that calculated (10.4%) for a tree-type structure having equal numbers of A- and B-chains. In addition, the simultaneous action of R-enzyme and 8-amylase can be used for the determination of CL (for details, see Ref. 144). 

Glycogenin and the mutant proteins, Phel94 and Thrl94, could also transfer glucose from UDP-Glc to maltose to form maltotriose." However, no further conversion to a higher oligosaccharide occurred. Analysis of the crystal structure by X-ray diffraction indicated that glycogenin existed similar to dimers." ... 

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-... 

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