Influence of Alcohols and Polyols on the Behavior of Aqueous Solutions of β-Lactoglobulin at pH 5.5

摘要

The above is a very brief survey of what we have found studying the thermody-namic behavior of β-lactoglobulin in the attempt to comprehend protein stability. The denaturing effect induced by alcohols and polyols depends clearly on the number of OH groups, as well on concentration. The behavior of thermal denatur-ation of aqueous solutions of β-lactoglobulin in alcohols and polyols of four carbon atoms shows that 1-butanol produces the largest decrease in T_m as alcohol concentration increases. The effect diminishes as the number of hydroxyl groups increase and for 1,2,3,4-butanetetrol, which is a typical hydrophilic solute, an increase in temperature is observed as concentration increases. In the case of butanediols, the decrease in T_m is greater for 1,2-butanediol, which has a larger hydrophobic domain due to the vicinal position of the OH groups, and with 1,2,4-butanetriol a negligible effect is observed. The number and position of OH groups is also clearly reflected on the surface and viscometric behavior of β-lactoglobulin in aqueous solution. The decrease of surface tension with alcohol mole fraction becomes less pronounced as the number of OH groups increases, while for 1,2,3,4-butanetetrol the behavior changes and the solution surface tension becomes larger than the corresponding value for water. The largest increase in activation energy is due to butanol, and diminishes as the number of OH groups increase. Experimental results reveal that thermal stability, surface tension and viscometric properties of aqueous solutions of β-lactoglobulin are clearly influenced by the presence of alcohols and polyols. The observed behavior follows a similar trend to that observed for the properties of these alcohols in water, suggesting that their effect on β-lactoglobulin stability is a consequence of the alcohol-water interaction and the induced modification in solvent structure, rather than alcohol-protein interactions.