3- Dextrine 0-amylase action

Pullulanase has great potential in structural investigations. In the case of amylose and its jS-limit dextrin, treatment with pullulanase has shown unambiguously (for the first time) that a-D-(l->6) branch-points form the natural barrier to heta-amylase action, that is, some amylose fractions have limited branching. ... 

It has been supposed that the amylase action leads to an equilibrium between starch and maltose or between maltose and certain dextrins. This is not the case, for if the limit dextrins are isolated and treated with amylase no action or at most only an extremely slow action is observed. 

Fig. 9.—Radioautograph of paper chromatogram showing radioactive Schardinger dextrins produced from radioactive glycogen by B. macerans amylase. Small amounts of linear oligosaccharides together with unreacted residues from the glycogen were removed by beta amylase action and converted to maltose and maltotriose.

In addition to their actions on disaccharides, the brush border enzymes further hydrolyze the products of amylase action, including maltose, maltotriose, and a-limit dextrins. The brush border enzymes appear to act in an integrated manner in that there is a flow of substrate from glucoamy-lase and isomaltase to sucrase with the production of the monosaccharides glucose, galactose, and fructose. These monosaccharides are transported into the ehterocyte by... 

Fig. 4.—Structures Around the Outermost Branch-points in the Limit Dextrins Remaining After Action of foeta-Amylase on Amylopectin and Glycogen. [Structure (b) is obtained uniquely by foeta-amylase action on phosphorylase limit-dextrins (see p. 315). For an explanation of the symbols, see footnote 49.]...

However, evidence in favor of a true structural feature that resists the action of fcefa-amylase has come from studies of the action of debranching enzymes on amylose and its hefa-limit dextrin. Thus, by treatment with yeast isoamylase, the befa-amylolysis limit of a sample of amylose was increased from 76 to 90 , and that of amylose 6e a-limit dextrin from 6 to 77 . Treatment of amylose with pullulanase also increases the conversion of the substrate into maltose by befa-amylase to an almost quantitative value. " On the basis of these results, the anomalous linkages in amylose that resist beto-amylase action are considered to be a very small proportion of (l->6)-a-D-glucosidic linkages. 

Figure 5. Photograph of a paper chromatogram of the products of macerans amylase action on a-dextrin with glucose or with glucosyl-(1,3)-arabinose at 0 time (A) and (C) and at 24 hr (B) and (D) ...

Amylase Action, Amylose is hydrolyzed to jS-maltose by jS-amylase. From the initiation of amylolytic action maltose appears, unlike the initial action of a-amylase which produces only dextrins. The picture of jS-amylase action is that it continuously hydrolyzes only the penultimate l,4 -a-glu-cosidic link from the non-reducing end of the amylose chain, so that in effect one maltose unit at a time is cleaved from the polysaccharide until all the amylose molecule is converted to maltose. ... 

The only example of this technique applied to the amylose component is that already described, of the action of Z-enzyme on the /3-limit dextrin. In the case of amylopectin, enzymic methods enable a distinction to be made between the proposed laminated and highly ramified structures (I and III, in Fig. 1, page 352). The method used by Peat and coworkers101 involves the successive action of /3-amylase and R-enzyme on waxy maize starch. /3-Amylolysis will degrade A-chains down to two or three units from the 6 —> 1-a-D interchain linkages. These latter linkages will protect the... 

---