Optical techniques to determine thermal effects on proteins

Optical rotation (OR) and transmitted light (TL) measurements were conducted on 1%, 2.5% and 5% (w/v) bovine serum albumin (BSA) in 0.01 m phosphate buffer at pH 7 and ionic strength 0.08. Denaturation temperatures (T_d) obtained from OR measurements were consistent with reported differential scanning calorimetry values. Protein concentration did not affect T_d in agreement with most reports. Changes in TL reflecting gel formation and protein aggregation were influenced by BSA concentration. Sugar concentration in the range used in this study (0-5%) did not affect the thermal stability of BSA. The lack of difference in sucrose, trehalose and sorbitol effects on the thermal stability of BSA was consistent with some but not all reports. The optical system used to study protein denaturation had acceptable accuracy (consistency with published T_d values) and precision (coefficient of variation under 3.5%) levels.