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A differential scanning calorimetric study of the conformational transitions of schizophyllan in mixtures of water and dimethylsulfoxide
Author(s) -
Kitamura Shinichi,
Kuge Takashi
Publication year - 1989
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360280208
Subject(s) - chemistry , differential scanning calorimetry , enthalpy , triple helix , solvent , helix (gastropod) , analytical chemistry (journal) , atmospheric temperature range , crystallography , stereochemistry , chromatography , organic chemistry , thermodynamics , ecology , physics , biology , snail
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°C and characterized by the specific enthalpy, Δ h cal = 3.29 J g −1 . A higher molecular weight sample, M‐2, showed this transition at 7°C with Δ h cal = 4.39 J g −1 . The transition temperature for both samples increased with increasing DMSO concentration up to about 50°C at 70 weight % DMSO, and then rapidly decreased with increasing DMSO concentration, with about 3°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 Δ h cal for both samples was a linear function of t 1/2 , the temperature of half‐completion in °C, Δ h cal = 0.177 t + 2.96. The triple helix‐coil transition was observed at around 127°C for U‐1 and above 130°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 Δ h cal vs. t 1/2 for the transition of both samples gave a linear relation, Δ h cal = 0.253 t – 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.