Differential scanning calorimetric studies on bovine serum albumin: III. Effect of sodium dodecyl sulphate.

Measurements of differential scanning calorimetry (d.s.c.) have been made on the complex bovine serum albumin (BSA)--sodium dodecyl sulphate (SDS) under various conditions. There are two peaks P1 and P2 in the d.s.c. curve for BSA at pH 7 and in the absence of NaCl, indicating the presence of the heat-induced transition of BSA. There are three peaks P1, P2 and P3 in the curve for the system with the molar mixing ratio SDS/BSA = 1. With the increase in the amount of SDS, the peak P3 grows at the expense of P1 and P2. There is only a single peak P3 in the curve for the systems SDS/BSA > 7, and no peak at SDS/BSA = 50 and 100. There is a single peak P12 in the curve for BSA at pH 7 and in the presence of 0.05 M NaCl, indicating that the heat-induced transition is suppressed. There are two peaks P12 and P3 for the systems SDS/BSA = 1-5; the area ratio of the peak P3 to P12 increases with the increase in the amount of SDS. There is only a single peak P3 when SDS/BSA > 7, and no peak at SDS/BSA = 50. It is concluded that the peak P3 is a product of SDS regardless of the presence or absence of NaCl. Values of thermal denaturation temperature (Td) and enthalpy (delta H) of thermal denaturation indicate that the complex AD12 (A = BSA, D = SDS) is in the most thermostabilized state.(ABSTRACT TRUNCATED AT 250 WORDS)