Effect of Sugars on Rabbit Serum Albumin Stability and Induction of Secondary Structure

The effect of sugars (sucrose, maltose, and glucose) on the thermal and chemical denaturation of rabbit serum albumin (RSA) has been examined by viscosity and far UV circular dichroism measurements. The viscosity measurements indicate a change in the reduced viscosity from 4.18 to 16.23 ml/g in the temperature range from 20 to 90°C. The Tm value for RSA obtained by viscosity measurements in the absence of sugar was found to be 63.2°C, but this value increased to 68.4, 70.3, and 73.2°C in the presence of 0.5 M sucrose, 0.5 M glucose, and 0.5 M maltose, respectively. Further, the stability of RSA in the presence of 0.5 M sugars was also investigated by measuring the mean residue ellipticity at 222 nm (MRE222) using chemical (0-6 M guanidine hydrochloride) and thermal (20-90°C) transition processes. At the midpoint of the chemical denaturation, the increase in the MRE values at 222 nm in the presence of 0.5 M sugars were of the same order as the increase in the Tm values, i.e., maltose > glucose > sucrose. Interestingly, a mixture of 0.25 M glucose and 0.25 M fructose showed a cumulative effect on the thermal as well as chemical stability as compared to 0.5 M sucrose alone. In the case of both thermal and chemical denaturation, there was an increase in the MRE222 values upon addition of various sugars, this indicating induction of secondary structure in the protein.