ISSN:
1435-1536
Keywords:
Soybean globulin fraction
;
DSC
;
thermal denaturation
;
two-state model
;
lyotropic effects
;
thermodynamic theory
;
hydrophobicity of proteins
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Thermal denaturation of soybean globulin fraction (SBGF) in diluted solution (protein concentration 0.15–0.63%) has been studied by the method of differential adiabatic scanning calorimetry. SBGF thermograms have two maxima. The low temperature maximum is consistent with denaturation of 7S component, while the high temperature maximum with denaturation of 11S components of this fraction. In the investigated range of protein concentrations the thermodynamic parameters (temperature and enthalpy) of denaturation of SBGF and its main components are constant. This fact suggests that differential adiabatic scanning calorimetry gives information purporting a change in the protein state at molecular level. The temperatures and enthalpies of denaturation of the main SBGF components linearly rise with increase of NaCl concentration. The slope of dependences of denaturation temperature on salt concentration,K s, is extremely large (nearly 20 K · l/mole). The elementary thermodynamic theory of lyotropic effects in thermal denaturation of proteins has been developed based on the two-state model and linear approximation of protein-salt interactions by means of the corresponding second virial coefficient. It shows that the dependences of thermodynamic parameters of thermal denaturation on salt concentration should be linear in the initial section. This conclusion is consistent with the experiment. The differences of enthalpies and entropies of transferring denatured and native forms of the main SBGF components from water into NaCl solution have been determined. They are positive and their quantity increases linearly with salt concentration. This fact is consistent with the concept to the effect that the main factor of salt influence on thermal denaturation of SBGF is confined to a decrease of protein hydration. The effect of protein nature on the quantity of lyotropic effect in thermal denaturation has been considered. Using simple considerations as a basis, the dependence of the ratio betweenK s and the denaturation temperature in water has been obtained, which characterizes the lyotropic effect, on the molar fraction of hydrophobic residues in the protein molecule. This dependence is linear and the lyotropic effect rises with increase in the content of hydrophobic residues. It is satisfactorily consistent with the experimental data on NaCl effect on thermal denaturation temperature for ichthyocol gelatin, ribonuclease, lysozyme, 7S and 11S SBGF components. An extraordinary strong influence of NaCl on thermal denaturation temperatures for the main SBGF components can be accounted for by a relatively high content of hydrophobic residues.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01413942
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