Amylopectin partial

Structural analysis of isolated amylose and amylopectin components has been carried out by standard methods based on methylation, periodate oxidation, and partial acid hydrolysis studies. Methylation and periodate oxidation studies established the linkage types and frequency of... 

Fig. 33. Experimentally observed molecular-weight dependence of (S2)z for amylose chains grafted onto glycogen (filled circles) and partially debranched amylopectin (open circles). Grafting was achieved by potato phosphorylase (15 rays for glycogen and 12000 per amylopectin molecule), and by muscle phosphorylase (400 rays per glycogen molecule)142,143)...

Starch is the main energy reserve of superior vegetal plants. It is found in big quantities in wheat, potato, com and manioc. Starch is a homopolymer (99%) of D-anhydroglucopyranose units. Nevertheless, two different configurations exist amylose and amylopectin (Figure 5.18). The proportion of branched polymer is 70-80% (Park et al., 2007). Native starch is present in the form of partially crystalline (25-40% ) granules (up to 100 pm diameter), showing a complex structure, which has been the object of thousands of scientific papers. 

Interaction of these mutants further clarifies the biosynthetic pathway. For example, the wx mutant is epistatic to all other known maize endosperm mutants and no amylose accumulates (Table 3.6). Mutants such as sh2, bt2 and sit cause major reductions in starch accumulation, but when in combination with wx, the starch produced is all amylopectin.271 In the double mutant ae wx, wx prevents the production of amylose and ae reduces the degree of branching, resulting in the accumulation of a loosely-branched polysaccharide.88 The su mutant is epistatic to du, su2 and wx relative to accumulation of phytoglycogen, but ae and sh2 are partially epistatic to su, causing a marked reduction in the su stimulated phytoglycogen accumulation (Table 3.6). The addition of du or wx to ae su partially overcomes the ae inhibitory effect, and phytoglycogen accumulates. 

Swinkels29 collected published characterization data for tapioca starch and compared it to that for other starches of commercial significance (Table 12.4). Tapioca starch is differentiated from other starches by its low level of residual materials (fat, protein, ash), lower amylose content than for other amylose-containing starches, and high molecular weights of amylose and amylopectin. The small amount of phosphorus in tapioca starch is partially removable30 and, therefore, not bound as the phosphate ester as in potato starch. It is also common to find protein and lipid values of zero, as reported by Hicks.31 The very low protein and lipid content is an important factor which differentiates tapioca starch from the cereal starches. 

Amylopectin Amylopectin, the insoluble fraction of starch, is also primarily an a-1,4 polymer of glucose. The difference between amylose and amylopectin lies in the branched nature of amylopectin, with a branch point about every 20 to 30 glucose units. Another chain starts at each branch point, connected to the main chain by an a-1,6 glycosidic linkage. A partial structure of amylopectin, including one branch point, is shown in Figure 23-20. 

Partial structure of amylopectin. Amylopectin is a branched a-1,4 polymer of glucose. At the branch points, there is a single a-1,6 linkage that provides the attachment point for another chain. Glycogen has a similar structure, except that its branching is more extensive. 

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