Dominant effect of ethanol in thermal destabilization of bovine serum albumin in the presence of sucrose

The thermal melting of bovine serum albumin (BSA) in the presence of excipients like ethanol and sucrose was studied by circular dichroism spectroscopy at physiological pH in phosphate buffered saline. Calculated apparent Tm values were used to assess the thermal stability using two state fitted experimental curves. 0.5 M sucrose stabilized the BSA indicated by the increase in Tm of ∼8 ◦ C when compared to the Tm of the same solution measured in the absence of sucrose. Conversely, in the presence of varying concentrations of ethanol (2-20%), the protein was destabilized by a decrease of ∼3-10 ◦ Co fTm. In the binary mixture of sucrose and ethanol, the Tm values showed that ethanol dominantly destabilized BSA in the presence of sucrose, possibly by weakening the hydrophobic interactions in the protein.