Binding of 6-propyl-2-thiouracil to human serum albumin destabilized by chemical denaturants

We compared the binding affinity of 6-propyl-2-thiouracil (PTU) with native and destabilized human serum albumin (HSA) as a model to assess the binding ability of albumin in patients suffering from chronic liver or renal diseases. Urea (U) and guanidine hydrochloride (Gu·HCl) at a concentration of 3.0 M were used as denaturation agents. sing the concentration of PTU from 0.8 × 10−5 to 1.20 × 10−4 M in the systems with HSA causes a decrease in fluorescence intensity of the protein excited with both 280 and 295 nm wavelengths. The results indicate that urea and Gu·HCl bind to the carbonyl group and then to the NH-group. To determine binding constants we used the Scatchard plots. The presence of two classes of HSA–PTU binding sites was observed. The binding constants (Kb) are equal to 1.99 × 104 M−1 and 1.50 × 104 M−1 at λex = 280 nm, 5.20 × 104 M−1 and 1.65 × 104 M−1 at λex = 295 nm. At λex = 280 nm the number of drug molecules per protein molecule is aI = 1.45 and aII = 1.32 for I and II binding sites, respectively. At λex = 295 nm they are aI = 0.63 and aII = 1.54 for the I and II binding sites. timation of the binding ability of changed albumin in the uremic and diabetic patients suffering from chronic liver or renal diseases is very important for safety and effective therapy.