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 che mical denaturation of rabbit serum albumin (RSA) has been examined by visco sity 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 degreesC. The T-m value for RSA obtained by viscosity measurements in the absence of sugar was found to be 63.2 degree sC, but this value increased to 68.4, 70.3, and 73.2 degreesC in the presen ce of 0.5 M sucrose, 0.5 M glucose, and 0.5 M maltose, respectively. Furthe r, the stability of RSA in the presence of 0.5 M sugars was also investigat ed by measuring the mean residue ellipticity at 222 run (MRE222) using chem ical (0-6 M guanidine hydrochloride) and thermal (20-90 degreesC) transitio n 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 o rder as the increase in the T-m values, i.e., maltose > glucose > sucrose. Interestingly, a mixture of 0.25 M glucose and 0. 25 M fructose showed a cu mulative 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 sugar s, this indicating induction of secondary structure in the protein.