Low-molecular-weight amyloses

The low molecular weight amylose-iodine-complex could be eluted with acetate buffer (pH 4,8, 0,1 M) containing 2 M urea (Figure l), but in case of high molecular weight amylose-iodine-complex (Figure 2), it was necessary to increase the concentration of urea to 8 M to achieve complete desorption. 

Another transferase reaction involves dextransucrase, which catalyzes the formation of dextran and some oligosaccharides (49). Yet another transferase reaction entails the use of potato starch phosphorylase in the synthesis of low-molecular-weight amylose (50). 

Phosphorolytic Synthesis of Low-Molecular-Weight Amyloses with Modified Terminal... 

Low-molecular-weight amylose having narrow polydispersity (GPC standard grade, AS-10 lot. No. 68, Mn = 1.0xl0 Mw/Mn = 1.05),... 

It should be noted that the different structures of amylose and amylopectin confer distinctive properties to these polysaccharides (Table II). The linear nature of amylose is responsible for its ability to form complexes with fatty acids, low-molecular-weight alcohols, and iodine these complexes are called clathrates or helical inclusion compounds. This property is the basis for the separation of amylose from amylopectin when starch is solubilized with alkali or with dimethylsulfoxide, amylose can be precipitated by adding 1-butanol and amylopectin remains in solution. 

Staudinger and Husemann determined the osmotic pressure of solutions of a potato starch acetate which had been fractionated into four parts by precipitation of its chloroform solution with ether. The molecular weights of the fractions ranged from 45,000 to 275,000. All of the fractions were soluble in chloroform, but fractions of low molecular weight were also soluble in acetone. For various concentrations of solute in either chloroform or acetone, the osmotic pressure did not increase in direct proportion to the solute concentration, but the deviation from van t Hoff s law was the smallest in the case of the acetone solutions. Osmotic pressure measurements on amylose and amylopectin tri-acetates dissolved in tetrachloroethane have been made by Meyer and co-workers, who have deduced molecular weights for these substances of approximately 78,000 and 300,000, respectively (see above discussion of the purity of these fractions). 

It is the amylose component of starch that gives the blue color when KI/I2 solution is added. To study the iodine-iodide color of amyloses of different d.p. values, maltodextrin-amylose molecules, with various avg. d.p. values from 6 to 568 were prepared by Bailey and Whelan [62], using phosphorylase, a-D-glucopyranosyl-1-phosphate, and maltohexaose. The colors of the various sized maltodextrins (1 mg) were observed when 10 1 (w/w) KI/I2 solution was added. The first color to be observed was faint red for avg. d.p. 12 a red-purple color was observed for avg. d.p. 31 a purple color was observed for avg. d.p. 40 and a blue color was observed for avg. d.p. 45. The increase in the blue value was linear as a function of avg. d.p. up to avg. d.p. 60 the absorbance at 645 nm then slowly increased and reached a maximum at avg. d.p. of 400. The intensity of the iodine/iodide color in the low molecular weight range was dependent on the concentration of the iodine. When the concentration of the iodine was increased 10-fold, the intensity was increased 50% [62]. 

In the carbohydrate field it has been found possible to separate mixtures of oligosaccharides differing in size by only one glucose unit. Dextrans of low molecular weight have been separated by gel filtration." Partial resolution of a number of starch dextrins on Sephadex columns has been reported." Thus amylodextrin can be separuled completely from amylose. The method is particularly useful for polysaccharides because they show only small differences in their properties and usually differ only in maleuiilur size. 

About 75% of the sizing agents used throughout the world today consist of starch and its derivatives because of its low cost. Chemically starch is composed of amylose and amylopectin. Amylose molecule is in the form of helix with six glucose units per turn (Fig. 3-1). The low molecular weight of amylose is water soluble... 

The action pattern of /8-amylase on substrates of low molecular weight is, therefore, established, but that with amylose of DP 10 remains to be examined further. 

Pretreatment of the maize amylose with a-amylase gave a series of linear maltosaccharides which were only slightly (about 8%) degraded by phosphorylase, indicating that the enzyme had little afiinity for substrates of low molecular weight. However, with high concentrations of enzyme, a reaction with maltoheptaose has been observed, in which disproportionation occurred with the formation of a series of oligosaccharides of DP... 

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