Triple helix of a schizophyllum commune polysaccharide in aqueous solution

Abstract

From sedimentation equilibrium, light scattering, and viscosity measurements on a series of native and sonicated samples of schizophyllan, and extracellular β‐1,3‐D‐glucan, the following results were obtained: (i) weight‐average and z‐average molecular weights (M̄w and M̄z) in water are about three times as large as those in dimethylsulfoxide (DMSO); (ii) the exponent in the Houwink‐Mark‐Sakurada intrinsic viscosity relation in water is close to 1.7, whereas in DMSO it is 0.68; (iii) intrinsic viscosities of samples with M̄w below 5 × 10 5 in water at 25°C can be fitted by Yamakawa's theory for along rigid rod if the pitch (1.836 nm) of the triple helix of Atkins et al. and the diameter (3 nm) estimated from the model triple helix are used; (iv) intrinsic viscosities in water‐DMSO mixtures at 25°C undergo and almost discontinuous decrease when the weight fraction of DMSO in the mixture increases to about 87%. These results combined lead to the conclusion that schizophyllan dissolves in water as a triple helix similar to that proposed by Atkins et al. and that the triple helix in aqueous DMSO solution “melts” abruptly to single chains when the DMSO coposition reaches about 87 wt%. It was also found that the triple helix is not recoverable once it is broken in DMSO.