Amylose helical interactions

Until recently, the location and state of amylose within granules was one of the most important questions remaining to be answered. Three main hypotheses for the location of amylose within starch granules have been put forward. The first hypothesis is that amylose is laid down tangentially to the radial orientation of amylopectin in order to minimize the amylose-amylopectin helical interactions.142 There is,... 

In summary, therefore, substantial information regarding the location and state of amylose has been obtained. Individual amylose chains are believed to be randomly located in a radial fashion among the amylopectin molecules. The concentration of amylose (and lipid) increases towards the surface of the granule, with smaller (leach-able) amylose chains predominating near the surface. Amylose chains are believed to be in a single helical state, although a small proportion may be involved in lipid complexes.147 Some of the larger (non-leachable) amylose chains may be involved in double helical interactions with amylopectin.159... 

Do double helical interactions between amylose and amylopectin chains occur within the granule ... 

Thus, randomly coiled amylose binds I3 ions, and this interaction is responsible for the helical structure of amylose. Helical amylose arrests iodine and further I3 anions, a process which is cooperative. If the filling of one helix commences, then the filling of another helix proceeds once the former helix is full. The longest available helix has priority in the uptake... 

CD bands for DP 1000 did not form a normal pattern. These results suggest that the high polymer complex possesses the deep bluing species in the aggregate of the amylose helices. The asymmetric shallowing of the CD bands can be ascribed to the increase of the foregoing exclton-coupled interactions as discussed in the previous section. 

Akiyoshi et al. reported on the behavior of amylose-block-polyethylene oxide in solution. Their results show that the amylose helix is quite expanded in chloroform solutions and/or a complete different microenvironment is involved [122,123]. These results are also supported by CD studies of the interaction of methyl orange with the amylose helices. 

Considering the linear chains and chain segments as short-chain (low molecular) -> amylose, similar interactions like those of amylose are possible. The crystalline regions of the - starch granules are formed by elementary cells of double helices, which are joined together by antiparallel unwinding. The main share of this starch crystallinity is due to a. 

Although the dipolar and resonating nature of the interaction of amylose and iodine is well established, Schlamowitz173 regards the iodine in a starch complex as being in a predominantly non-polar form, and Meyer and Bern-feld174 refute the helix theory and consider that adsorption of iodine occurs on colloidal micelles in amylose solutions. Most of the experimental facts which Meyer presents can, however, be satisfactorily explained on the helical model. 

Amylose is synthesized by granular-bound starch synthase, whereas amylopectin is synthesized by soluble starch synthase (Chapter 4).334,339 Because amylose is synthesized by the granular-bound starch synthase in a progressive manner,340 the amylose molecule is likely confined in the granule and has little opportunity to interact and form double helices with other starch molecules to facilitate branch formation. Branching reactions do occur on some amylose molecules, but at a much lower frequency than with amylopectin, and result in slightly branched amylose molecules. 

The discovery of the V-type, helical amylose (see p. 265) that forms when amylose interacts with 1-butanol was crucial for the development of the chemistry of starch inclusion complexes. It soon appeared that 1-butanol complexes solely with the amylose component. This selectivity became the first convenient method of fractionating starch. This method was first described by Schoch699 and later developed by Kerr et al.700-702 and oth-ers 680,703 An impr0ved procedure was subsequently patented.704 The amount of 1-butanol adsorbed in amylose is increased by the presence of moisture and is also dependent on two key factors the time of contact with that alcohol and the origin of the amylose, as shown in Table XXIX. 

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