Dextrins amylose limit

Amylase occurs in many plants, such as barley, wheat, rye, soy beans, and potatoes, where it is generally accompanied by some a-amylase. [ -Amylase initiates hydrolysis at the nonreducing end of an amylose or amylopectin chain, and removes maltose units successively until the reducing end of the molecule is encountered in amylose or a branch is met in amylopectin. ( -Amylase is used commercially in the preparation of maltose symps. After P-amylase hydrolysis of amylopectin there remains a P-amylase limit dextrin. ( -Amylase has been used as a probe of the fine stmcture of amylopectin (43-46). 

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... 

Using results of these kinds of studies, the characteristic structure of amylose can be differentiated from that of amylopectin. Amylose has a small number of branches and crystallizes and precipitates when complexed with 1 -butanol. The iodine affinity of amylose is much greater (i.a. 18.5 to 21.1) than that of amylopectin (i.a. 0.0 to 6.6),79,152-158,163,169-174 and the iodine affinity of amylose (3-limit dextrin is similar to that of the parent amylose. The average chain length of amylose (3-limit dextrins is much larger than that of the amylopectin (3-limit dextrin.160... 

Table 10.9 Molecular properties of wheat amylose and its beta-limit dextrins as affected by starch source232...

Pancreatic (a) amylase is an endoglycosidase, which removes maltose units from amylose or amylopectin. It splits the a-1,4 glycoside bond. In the absence of an a-1,6 glycosidase, limit dextrin is a product in addition to maltose. Sucrose is nonreducing lactose is reducing. 

Large molecules can also act as primers amylopectin and glycogen have been found to be the most efficient for potato and muscle phos-phorylases, respectively. The /3-limit dextrins of these substrates, however, have litde action. Amylose can also act as a primer. 

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. ... 

Amylopectin, when hydrolyzed in the presence of a-amylase, yields maltose and limit dextrins. However, amylose, under the same conditions, almost quantitatively produces maltose. This difference in behavior is best explained by ... 

In comparative studies of starch fractions, Wilson, Schoch and Hudson, and also Kerr, - showed that the amylose fraction of starch gave much higher yields of Schardinger dextrins (up to about 70 %) than did the amylopectin fraction. Starch modification or degradation products in general gave reduced yields especially with beta amylase limit dextrins or acid hydrolyzed starch sirups there was no detectable production of crystalline dextrins. 

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