Sugars and polyols stablize proteins against heat denaturation. Scanning calorimetry was used to obtain a quantitative estimate of the degree of stabilization. Solutions of ovalbumin, lysozyme, conalbumin, and alpha-chymotrypsinogen were heated at a constant rate, and the temperature of the maximum rate of denaturation was estimated (Tm). Addition of a sugar or polyol raised Tm. The magnitude of the stabilizing effect (delta Tm) depended on both the nature of the protein and the nature of the sugar or polyol, ranging from 18.5 degrees C for lysozyme at pH 3 in the presence of 50% (w/w) sorbitol to 0 degrees C for conalbumin at pH 7 in 50% glycerol solution. It is argued that this stablization is due to the effects of sugars and polyols on hydrophobic interactions. The strength of the hydrophobic interaction was measured in model systems in sucrose and glycerol solutions. Sucrose and glycerol strengthened the pairwise hydrophobic interaction between hydrophobic groups; however, they reduced the tendency for complete transfer of hydrophobic groups from an aqueous to a nonpolar environment. The extent of stabliziation by different sugars and polyols is explained by their different influences on the structure of water. The difference between the partial molar volume of the sugar or polyol and its van der Waals volume was used as a rough quantitative measure of the structure-making or structure-breaking effect. There was a linear relationship between this quantity and delta Tm.

SummaryOvalbumin is changed to a more stable form (S-ovalbumin) during the storage of shell eggs. Conversion also occurs in an isolated ovalbumin solution, the rate increasing with pH and temperature. First order rate constants for the reaction have been measured at pH 9-10 and at temperatures between 20 and 50°C. The reaction is apparently irreversible and does not appear to involve loss of" amino acids or small peptides.Ovalbumin and S-ovalbumin have been compared by measurements of sedimentation rates, molecular weights, electrophoretic and serological properties, sulphydryl and disulphide groups, ultraviolet absorption spectra, specific rotation, crystal form, and solubility. No difference which would explain their difference in stability was observed in the properties of the native proteins. Measurements of changes in specific rotation on denaturation in urea-guanidine hydrochloride solutions indicate more complete unfolding in ovalbumin than in S-ovalbumin.

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