Light Scattering Studies on the Denaturation of Bovine Serum Albumin in Urea Solutions

The mechanism of denaturation of bovine serum albumin (BSA) in various urea solutions was studied by means of the light-scattering and viscosity methods. The measurements were made over a wide range of the urea concentration including the low concentrations of urea and the results were compared with those in the case of guanidine hydrochloride. When the urea concentration was below 5.5M, values of degree of denaturation, intrinsic viscosity, and second virial coefficient of BSA were not much different from the values of native state, but these values increased remarkably at above 5.5M. It is seen from these results that the mechanism of denaturation differs below and above 5.5 M of urea (about 0.9 in degree of denaturation). As for the molecular weight of BSA, the relation, M=(7.09+1.17C3)×104, was obtained between urea concentration C3 (mole/liter) and apparent molecular weight, M. Because these values were smaller than those in the case of guanidine HCl, it is concluded that the denaturation ability of urea was weaker than that of guanidine HCI. The major axis of the aggregated BSA as a prolate spheroid changed remarkably, but the minor axis took constant values at higher concentration of urea. It is, therefore, concluded that molecules of intramolecularly denatured BSA aggregate end-to-end to form aggregates of an elongated shape.