Effect of guanidine hydrochloride on bovine serum albumin complex with antithyroid drugs: fluorescence study

Denaturation of bovine serum albumin (BSA) with guanidine hydrochloride (Gu·HCl) was studied in the presence of mercaptopyrimidine (MPI) and uracil. With increasing unfolding of albumin due to Gu·HCl presence, the displacement of both MPI and model compound - uracil occurs. The spectroscopic analysis suggests that uracil and MPI binding sites are close to or located in the IB or IIA subdomains. Binding of both uracil and MPI to unfolded BSA is observed. The antidenaturant properties of uracil are shown. The binding and quenching constants were calculated for the uracil-BSA complex and in the presence of the denaturant (Gu·HCl). Structural changes due to 1.7 M Gu HCl led to the lowering of the binding constant by ,14%. These changes rise with unfolding BSA. q 2004 Elsevier B.V. All rights reserved.