Light Scattering Studies on the Thermal Denaturation of Bovine Serum Albumin

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Thermal denaturation of bovine serum albumin (BSA) was studied by means of light scattering and viscosity measurements. The degree of denaturation (wD°) was measured by using HABA, an anionic dye. The values of intrinsic viscosity, weight-average molecular weight and radius of gyration showed no appreciable changes when wD° was within 85 percent, but increased remarkably when wD° exceeded 85 percent. Thus, it has been concluded that the thermal denaturation proceeds in two steps, i.e., intramolecular denaturation in the earlier stage and intermolecular association in the later stage. Analysis of the light-scattering data showed that the aggregated molecule was in a rod-like shape, whose length increased almost linearly with the weight fraction of the aggregated molecule wn, the latter being obtained by analysis of the refractive index increment. On the other hand, the diameter did not change with the degree of denaturation, and its value was about 140 Å, which is almost equal to the largest dimension of the native BSA molecule. It has been concluded that the BSA molecules form aggregates by side-by-side association, whose length is about 2910 Å and diameter about 140 Å.
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