Amylosic chain models

Figure 1. F(ii) = NiJP(ii) vi. ii = (4t/ K) sin (e/2) for helical amylosic chain nwdels A, B, and C, wormlike amylosic chain model W, jointed helical model J, and realistic random coil model R. Details of the models are described in the text.

Monte Carlo calculations of the Debye scattering function P i) for several amylosic chain models suggest that it may be possible to distinguish experimentally between popular generic models for the amylosic chain by investigating the angular dependence of... 

A) Circular amylose-GA-1 complex and (B) corresponding binding model the balls represent starch-binding domain (SBD) and the lines represent amylose chains (C) linear amylose-mutant GA-1 complex and (D) corresponding binding model. Image size ... 

Figure 14. Directional correlation function as in Fig. 8 for amylosic chains based on the rigid residue model (filled circles) and relaxed residue model (open circles).

Figure 15. The mean trajectories of amylosic chains based on the rigid residue (filled circles) and relaxed residue (open circles) models projected into the XY plane of a coordinate system attached to a terminal residue. Circles represent the mean positions of successive glycosidic oxygens in the primary sequence. The persistence vector (mean end-to-end vector) for a chain of x residues is the vector (not shown) connecting the origin and the mean position of the glycosidic oxygen separated from it along the chain by x virtud bonds.

The earliest attempts at model analysis of polysaccharides -typified by the x-ray crystal structure analysis of amylose triacetate - were usually conducted in three steps ( L). In the first step, a model of the chain was established which was in agreement with the fiber repeat and the lattice geometry, as obtained from diffraction data. In the second step, the invariant chain model was packed into the unit cell, subject to constraints imposed by nonbonded contacts. This was followed, in the third step, by efforts to reconcile calculated and observed structure factor amplitudes. It was quickly realized that helical models of polysaccharide chains could be easily generated and varied using the virtual bond method. Figure 1 illustrates the generation of a two-fold helical model of a (l- U)-linked polysaccharide chain. 

The vrork reported here has beat carried out in the context of a program to develop reliable conformational energy functions for polysaccharides in solution U, ). A quite satisfactory model for aqueous amylosic chains has been developed details are reported at length elsevdtere P, ). Here procedures... 

The number of observables described here is not sufficient to determine uniquely the several parameters of the theory. We can, however, assign p and u on the basis of independent information concerning the conformation of aqueous amylosic chains in the absence of iodine. A realistic model of aqueous amylose (31) discloses that perhaps 25% of an amylose chain in water might be classified as nearly regular helix at any instant, but the chain conformation is extremely labile, and there is no evidence for any conformational cooperativity in the absence of iodine. Hence, the cooperativity parameter u may be set equal to unity, and for convenience we also take p = 1, which implies equal proportions of helix and coil in the absence of iodine. Calculations not reported in detail here reveal that the results described below are quite insensitive to the exact numerical value of p, provided u = 1 and p is of order unity. 

The problem whether or not a helical structure of amylose is retained in solution is nearly as old as the discovery of the V-amylose helix from X-ray data in 1943 (7 ) and has been the subject of extensive investigation and controversy. (For review see ( )). At present mainly two models are considered the "extended helix chain" 9) and the "randomly coiled pseudohelical chain" (10). According to Senior eind Hamori (9) the amylose chain conformation is characterized by loose, extended helical regions, which are interrupted by short, disordered regions. Hydrogen bonds between 0(2) and 0(3 ) of neighboring residues are... 

ABSTRACT. The interaction of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) with amylose and its related compounds in aqueous solution has been studied by both steady-state and transient fluorescence measurements. The fluorescence of TNS aqueous solution was enhanced by the addition of amylose, 3-limit dextrin, and amylopectin. The fluorescence decay of TNS bound to these polysaccharides were well described as a sum of two-exponential functions. This suggests that there are two different microenvironments at the binding sites. The fluorescence lifetime of major component for TNS-amylose system agreed with that of major component for TNS-y-cyclodextrin system. The mean rotational relaxation time of TNS bound to amylose is similar to that of the segmental motion of amylose chain. Based on these results, a configurational model for TNS-amylose complex has been proposed. 

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