Stability of the complex BSA-6-propyl-2-thiouracil in the presence of Gu·HCl and urea

Pathologic structure of albumin is present in blood of uremic or diabetic patients. The defective binding of albumin can cause, among others, inhibition of the metabolism of amphipathic hormones and the enhancement of the toxicity of drugs. to show the alteration of the binding site of 6-propyl-2-thiouracil (PTU) in bovine serum albumin (BSA) in the presence of urea and guanidine hydrochloride. This study shows that PTU has the tendency to interact within the hydrophobic domain IIA or IB of serum albumin and to quench the fluorescence of tryptophanyl side chains by the static and collisional quenching mechanism. e binding to the native protein, two classes of binding sites are seen. In the first one, the binding constant is equal to KbI−9.6×104 M−1, and in the second class, the binding constant is KbII−7.1×103 M−1. For the binding to the denaturated serum albumin, only one class of the binding sites can be observed. The binding constants for BSA denatured with urea and Gu·HCl are lower and are equal to 2.2×104 M−1 and 3.5×104 M−1, respectively. tion of the binding ability of serum albumin is also important in case of older people because weaker drug–protein interaction can result in the increase of drug concentration in the blood serum.