Takashi Norisuye

Correlation between the antitumor activity of a polysaccharide schizophyllan and its triple-helical conformation in dilute aqueous solution

Eight samples of a polysaccharide schizophyllan ranging in weight-average molecular weight Mw (in water) from 5 x 10(3) to 1.3 x 10(5) were prepared and their antitumor activity (expressed in terms of the tumor inhibition ratio) against Sarcoma 180 ascites, intrinsic viscosities [eta], and gel-filtration chromatograms in aqueous solution were determined. The tumor inhibition ratio was essentially unity for samples with Mw higher than 9 x 10(4), but reduced to zero or even to a negative value when Mw was lower than 10(4). The [eta] data combined with the chromatographic data showed that above Mw approximately 9 x 10(4) the predominant species of schizophyllan in aqueous solution is the previously found rigid triple helix, whereas below Mw approximately 9 x 10(4) both triple helices and single chains coexist in the solution and the fraction of triple helices decreases monotonically to zero as Mw is decreased to 5 x 10(3). From these findings it was concluded that the antitumor potency of schizophyllan in water is related to the amount of triple helices relative to that of single chains.

Thermally induced conformational change of xanthan in 0.01m aqueous sodium chloride

Abstract Light-scattering and viscosity measurements were made on five sonicated samples of sodium xanthan in 0.01M aqueous NaCl at 25 and 80°, temperatures at which the polysaccharide is known to take on certain ordered and disordered conformations, respectively. For two of these samples, measurements were also made at different temperatures between 25 and 80°. From the data obtained for weight-average molecular weight M w , radius of gyration, and intrinsic viscosity, the following conclusions were derived. ( 1 ) The ordered conformation of Na xanthan in 0.01M aqueous NaCl at 25° is essentially the same dimerized, double helix as that found previously in 0.1M aqueous NaCl. ( 2 ) When the temperature is raised from 25 to 80°, the dimer does not dissociate to single chains, but its statistical radius decreases, or remains unchanged, depending on its M w . ( 3 ) The disordered conformation at 80° is well represented by a model in which four wormlike chains are joined together by a very short double-helical segment. ( 4 ) The thermally induced, order-disorder conformational change of xanthan in 0.01 m aqueous NaCl is the process of partial melting of the double helix.

Melting behavior of Schizophyllum commune polysaccharides in mixtures of water and dimethyl sulfoxide

Abstract The triple helix of a polysaccharide Schizophyllum commune (schizophyllan) of viscosity-average molecular weight 4.8 x 10 5 g.mol −1 (in water) was melted at denaturation temperatures T d between 5 and 60° in water-dimethyl sulfoxide (Me 2 SO) mixtures. The solutions for different T d values were studied by viscometry and ultracentrifugation. AsT d was increased, the intrinsic viscosity of the mixture containing 12.76% (by weight) of water decreased sharply and, at about T d  50°, it approached the value expected for the single chain of schizophyllan in pure Me 2 SO. Schlieren patterns of the sample “denatured” at T d between 25 and 45° in the same mixed solvent showed the presence of two solute species. The fast-sedimenting species dominating at T d  25° almost disappeared at T d  45°. From sedimentation-coefficient data for the mixture, pure water, and Me 2 SO, the fast- and slow-sedimenting species could be identified with the triple helix and the single chain of schizophyllan, respectively. These findings allow us to conclude that, in water-Me 2 SO mixtures containing ∼ 13% of water, the schizophyllan triple-helix melts into single chains in all-or-none fashion with increasing temperature.

Solution properties of synthetic polypeptides. VI. Helix–coil transition of poly-N5-(3-hydroxypropyl)-L-glutamine

A new procedure for evaluating u and σ characterizing σ‐helix‐forming polypeptides in solution was derived from Nagais theory for the helix–coil transition of such polymers. Here u is the activity for helix formation from random coil, and σ is the helix initiation parameter. The necessary data are the helical content fN at fixed solvent and temperature as a function of N, where N is the degree of polymerization of the polypeptide sample. Such data were obtained from ORD measurements on a number of fractionated samples of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine (PHPG) in mixtures of water and methanol covering the complete range of composition and at various termperatures (5–40°C). When analyzed in terms of the proposed procedure, they yielded values of σ which were in the range (3.2 ± 0.6) × 10−4, substantially independent of solvent composition and temperature. These values were much larger than those obtained recently for σ of poly(β‐benzyl‐L‐aspartate) in m‐cresol and in a mixture of chloroform and DCA. The data for [η] and s0 (limiting sedimentation coefficient) as functions of molecular weight indicated that the molecular shape of PHPG in pure methanol is essentially rodlike, whereas that in pure water is not entirely randomly coiled but rather may be regarded as an interrupted helix. These indications were consistent with the results from ORD measurements. When plotted against the corresponding values of fN, the values of [η] and [s0] for PHPG in mixtures of water and methanol of various compositions and temperatures formed smooth composite curves, and we attributed these phenomena to the fact that σ of PHPG was nearly constant under these solvent conditions. Here [s0] stands for a reduced limiting sedimentation coefficient which is equal to the inverse friction factor of the solute molecule.

Excluded‐Volume Effects in Dilute Polymer Solutions. I. Equilibrium Properties

Data of the statistical radius 〈 S2 〉1 / 2 and the second virial coefficient A2 were obtained for sharp fractions of polychloroprene (PCP) in methyl ethyl ketone (MEK), n‐butyl acetate, and carbon tetrachloride at 25°C and in trans‐decalin at temperatures ranging from 1° to 50°C. MEK at 25°C and trans‐decalin at 2°C were found to be theta solvents for PCP. From these data two dimensionless quantities defined by αs2 = 〈 S2 〉 / 〈 S2〉0and Ψ = A2M1/2[4π3/2NA( 〈 S2 〉 / M3 / 2]−1 were calculated for all combinations of molecular weight M, solvent species, and temperature, where 〈 S2 〉0 is the value of 〈 S2 〉 under θ conditions and NA is Avogadros number. These two quantities should be functions of a single parameter z, usually known as the interaction parameter, which is proportional to M1/2. With the data for these quantities from the present experiments on PCP as well as from Berrys experiments on polystyrene, comparative tests of typical theories for the excluded‐volume effects on dilute polymer solutions ...

Viscosity behaviour and persistence length of sodium xanthan in aqueous sodium chloride.

Zero-shear-rate intrinsic viscosities [eta] of sodium xanthan in aqueous NACl at 25 degrees C were determined for five samples ranging in weight- average molecular weight from 2 x 10(5) to 4 x 10(6) at salt concentrations Cs between 0.005 and 1 M, at which the polysaccharide maintains its double-helical structure. The measured [eta] for every sample was almost independent of Cs, in contrast to usual observations on flexible polyelectrolytes. The persistence length q of sodium xanthan was determined as a function of Cs by use of the theory of Yamakawa et al. for [eta] of an unperturbed worm-like cylinder, and from its Cs dependence the intrinsic persistence length q(o) ( = q at infinite ionic strength) was estimated to be 106 nm. This q(o) value was roughly twice as large as that of double-stranded DNA, indicating a high intrinsic rigidity of the xanthan double helix. The electrostatic contribution ( = q - q(o)) to q was only about 10% even at the lowest Cs of 0.005 M. Thus, it was concluded that above Cs = 0.005 M, the double- helical structure of sodium xanthan is hardly stiffened by electrostatic interactions between charged groups.

Excluded‐Volume Effects in Dilute Polymer Solutions. II. Limiting Viscosity Number

Measurements of [η] were made for seven fractions of polychloroprene (PCP) in methyl ethyl ketone, n‐butyl acetate, and carbon tetrachloride at 25°C and for three fractions of PCP in trans‐decalin at a number of temperatures ranging from 0.05° to 65°C. On a log–log graph paper, the values of αη3( = [η]/[η]θ) calculated from these data formed a composite curve when plotted against αs3( = 〈S2〉3/2/〈S2〉03/2) obtained from light‐scattering experiments under the same conditions. This curve is characterized by a relatively marked upward curvature in the vicinity of the origin, followed by a linear portion of unit slope. Its initial tangent has a slope of 0.65, which is much smaller than 0.81 predicted theoretically by Kurata and Yamakawa. Plots of αη3 vs the interaction parameter z were prepared by evaluating z for each αs by use of the Yamakawa equation. They were fitted by a single curve having a slight downward curvature, suggesting that no drainage effect manifests itself in the viscosity behavior of the sys...

Some Topics Concerning the Radius of Gyration of Linear Polymer Molecules in Solution

Fixmans integral for the distribution function P(S2) obeyed by S2 of the unperturbed polymer chain was evaluated analytically, and its asymptotic forms valid for t ≪ 1 and t ≫ 1 were derived. Here S is the radius of gyration of the chain and t is the ratio of S2 to its statistical average 〈S2〉. The values of P(S2) calculated from the analytic solution agreed with Koyamas computer values over the entire range of t. The leading term of the asymptotic form for t ≪ 1 confirmed the previous result of Fixman. The asymptotic form for t ≫ 1 agreed not with Fixmans but with that of Forsman. The Flory–Fisk theory for the excluded volume effect in polymer chains was reformulated with the exact form being substituted for P(S2) in their basic equation for αs2. Here αs is the linear expansion factor of a polymer molecule defined in terms of 〈S2〉. The calculated curve for αs3 as a function of the interaction parameter z differed markedly from that derived by Flory and Fisk who had employed an approximate expression f...

Thermally induced conformation change of xanthan: interpretation of viscosity behaviour in 0.01 m aqueous sodium chloride

Abstract Zero-shear rate intrinsic viscosities [ν] and specific rotations [α] 300 at 300 nm wavelength were determined as functions of molecular weight and temperature T for sodium salt xanthan in 0.01 M aqueous NaCl, in which the polysaccharide undergoes an order-disorder conformation change with increasing T . The molecular weight dependence of [ν] at 25 and 80°C was consistent with the previous conclusion that the predominant conformation of Na xanthan at the former T , i.e. in the ordered state, is a rodlike double helix, while that at the latter T , i.e. in the disordered state, is a dimerized coil expanded by electrostatic repulsions. As T increased from 25 to 80°C, [ν] decreased or increased depending on the samples molecular weight, whereas [α] 300 sigmoidally increased for any samples studied. The striking temperature dependence of [ν] could be explained qualitatively in terms of the mean-square radius of gyration, a property analogous to [ν], calculated for a dimer model in which the double helix melts only from both ends.

Liquid Crystal Formation in Aqueous Solutions of a Polysaccharide Schizophyllan

Abstract Concentrated aqueous solutions of a triple helical polysaccharide schizophyllan with molecular weight 4 * 105 were investigated by polarizing microscopy and laser light diffraction at 30[ddot]C. The solutions were birefringent above a polymer weight fraction w of about 0.098, indicating the formation of a liquid crystalline phase. This liquid crystalline phase resembled in many respects cholesteric mesophases reported for polypeptide liquid crystals, and was found to be also cholesteric. It was characterized by a cholesteric pitch of the order of several μm varying approximately in proportion to w −1.9. The system studied was completely liquid crystalline above w = 0.127 but biphasic in the range of w between 0.098 and 0.127, and underwent an isotropic-liquid crystalline phase transition when the temperature was changed.