Volume 8, Number 1, p.p. 3-12
Rôle of sugar osmolytes in the stabilization of yeast alcohol dehydrogenase during heat stress
Venus Ravanmehr,1 Abdol-Khalegh Bordbar,1,* Mehran Miroliaei,2 and Asghar Taheri-Kafrani1
1Laboratory of Biophysical Chemistry, Department of Chemistry, University of Isfahan, Isfahan, 81746-73441, I.R. Iran
2Department of Biology, University of Isfahan, Isfahan, 81746-73441, I.R. Iran
Thermal denaturation of yeast alcohol dehydrogenase in the absence and presence of various concentrations of mannitol, sorbitol, sucrose and trehalose as sugar osmolytes and polyols was studied by observing changes in the absorption coefficients of the enzyme in 50 mM phosphate buffer, pH 7.80. A comprehensive thermodynamic analysis was done on all of the denaturation curves in order to construct the protein stability curve and estimate all the thermodynamic parameters of denaturation. It has been observed that all of these osmolytes affect the denatured state of the enzyme more than its native state, leading to a change in protein stability. While the melting temperature of YADH, Tm, is increased in the presence of these osmolytes, no certain trend is observed in the free energy change, ΔGiD, and enthalpy change at Tm, ΔHm, of denaturation. However, mannitol and sucrose at a concentration of 1 M increase ΔGiD to 26 and 45 kJ/mol, respectively. The temperature that corresponds to maximum protein stability, TS, is increased in the presence of these osmolytes in most cases. The same trend was also observed for TH, the temperature corresponding to zero enthalpy change of denaturation.
Keywords:
protein stability, sugar osmolytes, thermal denaturation, yeast alcohol dehydrogenase