The thermal conformational transitions of two sonicated samples of schizophyllan were studied in water-dimethylsulfoxide (DMSO) mixtures by high-sensitivity differential scanning calorimetry (DSC). Two transitions were observed over most of the range of solvent compositions. These were assigned to an internal change of the triple helix [T. Itou et al. (1986) Macromolecules 19, 1234-1240] and a triple-helix-single-coil transition [T. Sato et al. (1981) Carbohydr. Res. 95, 195-204], respectively. In water, the former transition observed at lower temperature for a low molecular weight sample, U-1, is centered at 3 degrees C and characterized by the specific enthalpy, delta hcal = 3.29 J g-1. A higher molecular weight sample, M-2, showed this transition at 7 degrees C with delta hcal = 4.39 J g-1. The transition temperature for both samples increased with increasing DMSO concentration up to about 50 degrees C at 70 weight % DMSO, and then rapidly decreased with increasing DMSO concentration, with about 3 degrees C higher for M-2 than for U-1 over the DMSO concentration. The transition was not observed when the concentration of DMSO exceeded 87%. It was found that delta hcal for both samples was a linear function of t 1/2, the temperature of half-completion in degrees C, delta hcal = 0.177t + 2.96. The triple helix-coil transition was observed at around 127 degrees C for U-1 and above 130 degrees C for M-2 in the range of DMSO composition below about 70%. The transition temperature decreased with increasing DMSO concentration at above 70%, and the transition finally disappeared when the DMSO concentration exceeded 90%. The plot of delta hcal vs. t 1/2 for the transition of both samples gave a linear relation, delta hcal = 0.253t - 10.58. The reversibility of the transition at lower temperature was demonstrated by the reversibility of the curves when the first heating was stopped before the second transition. Once the heating was performed over the second transition, the reheating DSC curves showed several endothermic peaks, indicating the irreversibility of the transition and heterogeneity in the conformation of the heated schizophyllan.

X‐ray diffraction analyses of the complexes of amylose with a wide variety of fatty acids were carried out. The unit cell dimensions of the complexes were calculated for both the wet and dry states. Both the 61‐ and 71‐helical conformations of amylose were found in these complexes, and the conformation seems to depend on the linear chain length of the acid molecules. The orthorhombic unit cell was proposed for the 71‐helical structure of the wet complexes. The dibasic acid gave the crystal modification of the complexes exhibiting the diffraction pattern of hexagonal or orthorhombic nature. It was also found that complexations with n‐propionic acid give rise to three kinds of the patterns, depending on the amount of n‐propionic acid added to aqueous solution of amylose.

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High molecular weight polysaccharide structure is conventionally described in terms of linear, comb-like, or treelike molecules. At a higher level of organization, various single-and multiple-stranded helical geometries have been described in addition to the less well-defined structures and connectivities that occur in noncovalently cross-linked gels. We report here on the finding of circular morphology in one type of high molecular weight multistranded polysaccharide. Circular structures have been described for synthetic polymers and DNA,' but except for the oligomeric cyclodextrins' and cyclosophoraoses,3 circular morphology of high molecular weight polysaccharides has not been reported previously.Samples of schizophyllan,' which dissolve as rigid, triple-helical structures in aqueous solution and random coils in dimethylsulfoxide (DMSO) ,' were subjected to renaturating conditions by dialysis against distilled water of the DMSO solutions. Electron microscopic (EM) observations of heavy metal replicated, vacuum dried specimen^^,^ obtained from the powdered polysaccharide dissolved in aqueous solution revealed almost exclusively linear structures. The limited resolution imposed by the used preparation technique does not allow observations of the side chains in the comb-like schizophyllan structure. Dissolution in DMSO with renaturation by dialysis to aqueous solution at high polymer concentration, i.e., c > 4 mg/mL, yielded predominantly aggregated structures, whereas mixtures of circular, linear, and aggregated structures were observed as a result of lowering the polymer concentration to about 1 mg/mL or below during the dialysis procedure. Circular structures were also observed in samples of lentinan. This is a polysaccharide with a chemical structure similar to that of schizophyllan which has received recent attention for its biological activity and which is currently used as a chemostatic agent in cancer therapy.8Schizophyllan dissolved in mixtures of water and DMSO is reported to undergo two transition^.^ The lowtemperature transition, occurring in pure water near 5"C, is reversible (Figure 1 ) , whereas the triple-helix to random Replicas for EM were prepared as described6 from schizophyllan solutions subjected to different temperature-solvent composition histories. The sample dissolved at W H = 1 is referred to as the starting material; the renaturated sample refers to a sample initially dissolved at w H = 0.0 and subsequently dialyzed against 7 X 1000 mL distilled water at 25°C for 96 h (Figure 1, dashed line). Aliquots of the renatured sample were subsequently heated to 115°C and kept for 2 h (flushed with N2 prior to heating) in a pressurized chamber before being slowly cooled to 25°C. The latter sample is referred to as annealed. Thus, the renatured sample is first carried through the allegedly irreversible random-coil to triple-helix transition and subsequently through the reversible transition. The annealing procedure was selected to enter the onset, but not go through, the triple-helix to random c...

ABSTRACT:The segmental motion of amylose in aqueous solution and the conformational transition with temperature and pH were studied by the fluorescence polarization method. We prepared two types of fluorescent conjugates of amylose: amylose conjugated with fluorescein randomly throughout chain (F-Amylose) and amylose conjugated locally on a terminal segment (I-F-Amylose). The value of the rotational relaxation time for t-F-Amylose was much smaller than that for F-Amylose. This result suggests that a terminal segment undergoes a more rapid microBrownian motion than interior segments. Polarization curves of these conjugates gradually departed from the Perrin equation when the temperature was raised. F-Amylose showed a gradual departure above 45°C but t-F-Amylose showed a departure at room temperature. This indicates that the conformational transition occurs first in terminal segments and then extends to the interior segments with increasing temperature. The effect of pH on the polarization was also examined. When measured as a function of pH, fluorescence depolarization increased pronouncedly in the alkaline region. In contrast to changing temperature, depolarization began to increase at the same pH for the two amylose conjugates.KEY The conformation of amylose in an aqueous solution has been intensively studied by means of hydrodynamic methods. ' -4 These studies suggest that amylose behaves as a random coil in an aqueous solution. It is therefore considered that an amylose chain takes on many different shapes and fluctuates continuously among these. However, we note that hydrodynamic measurements can provide information only about the overall character of the molecule. The local conformation of amylose in an aqueous solution is a matter of dispute in spite of extensive investigations. 5 • 6 measuring the fluorescence polarization of the attached dye residue. 7 -9 The fluorescence polarization method is expected to provide information on the segmental motion and the conformation of a polymer chain to which a fluorescent residue is attached. Thus, when a polymer chain undergoes a conformational transition, the course of the transition may be followed byThe purpose of the present study is twofold: to obtain information on segmental motion and the conformation of amylose about the attached dye residue and to study the conformational transition of amylose induced by temperature and pH changes, both by the fluorescence polarization method. We prepared two types of fluorescent conjugates of amylose: amylose conjugated randomly with fluorescein residues throughout the chain and amylose conjugated only at a terminal segment. These fluorescent conjugates enabled us to investigate the differences in segmental mobility and conformation between the interior and terminal segments of amylose.