Inter-chain linkages

Fig. 1.— Molecular Structures for Glycogen (a) Haworth laminated form, (b) Staudinger comb form, and (c) Meyer tree form. Key —Linear chain of Qi-(1 — 4)-linked D-glucose residues J, Inter-chain linkage [1—>6-glucosidic in structures (a) and (c) 1 2, 1 — 3, and 1 6-glucosidic in (b)] A, B, and C are...

Peat and coworkers"" have similarly characterized the inter-chain linkages in baker s-yeast glycogen. n-Glucose, maltose, isomaltose, and... 

Periodate-oxidation studies have thus shown that, in several glycogens, over 99 % of the inter-chain linkages are (1- 6), and experiments emplo5nng partial hydrolysis hy acid indicate that these linkages have an a-n-con-figuration. 

Glycogens are attacked by three known groups of enzymes amylases and phosphorylases degrade a-D-(l 4)-linkages, whilst a-D-(l 6) inter-chain linkages are hydrolyzed by debranching enzymes. -... 

Fig. 1.—Multi-brancted Structure for Amylopectin or Glycogen. (Key —, linear chain of (1 — 4)-linked a-D-glucose residues inter-chain linkage E, free reducing group A, A-chain B, B-chain C, C-chain E, exterior chain and I, interior chain.)...

With the recent identification of the anomalous linkages in amylose as a-D-(l 6)-glucosidic inter-chain linkages, the metabolism of starch and glycogen can be adequately considered in terms of the enzymic synthesis and degradation of only two types of n-glucosidic linkage, namely, a-D-(l— 4) and a-n-(l- ). 

Several different carbohydrases which will degrade a-D-(l— 6)-glucosidic inter-chain linkages (that is, debranching enzymes) are now known, but the susceptibility or nonsusceptibility of an inter-chain linkage depends upon its exact location in the substrate molecule, and, in particular, on the... 

Fig. 2.— Formation of Inter-chain Linkage by Q-Enzyme. (Key O— (1 a-D-glucose residue —> inter-chain linkage.)...

Q-Enzyme has no action on amylopectin, so that a polysaccharide containing about 5% of (1—>6) inter-chain linkages appears to be the highest degree of branching obtainable under in vitro conditions. 

Since treatment of various samples of amylose with yeast isoamylase (see p. 427) caused a significant decrease in specific viscosity and a corresponding increase in / -amylolysis limit, it seems probable that some amylose molecules have a low degree of branching, and that the inter-chain linkages are of the a-D-(l—>6)-glucosidic type, as in amylopectin. However, all samples of amylose do not contain barriers to 3-amylolysis, as shown by the isolation of amylose of molecular weight 2 X 10 and /3-amylolysis limit 95% by dispersion of starch in dimethyl sulfoxide. ... 

Segment of amylopectin or glycogen near an inter-chain linkage... 

From the structures of the smallest oligosaccharides produced at the second stage of amylolysis, it is evident that certain (1— 4)-linkages adjacent to the inter-chain linkage are resistant. These are shown in Fig. 9. The actions of A. oryzae and pig pancreatic a-amylases again appear to be identical with that of the human salivary enzyme. ... 

The yeast Saccharomyces diastaticus produces a related n-glucose-pro-ducing amylase which cannot hydrolyze inter-chain linkages but can bypass them with the formation of n-glucose and a branched trisaccharide. 

Inter-chain linkages in the interior of amylopectin are not hydrolyzed by R-enzyme, presumably for steric reasons, and amylopectin R-dextrin has a i3-amylolysis limit of only 70%. Moreover, glycogen of normal CL (10-14) is not attacked, although glycogen with CL 18 shows a small increase in /8-amylolysis limit (from 51 to 58%). ... 

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