Abstract: From reasonable suppositions on binding process and Langmuir’s binding theory, the interactions between 5-fluorouracil (5-FU) and bovine serumalbumin (BSA) were investigated by the isothermal titration calorimetry (ITC) and the circular dichroism (CD) spectrometry at 298.15 K. The results showed that there were two classes of binding sites on a protein (BSA) molecule for the 5-fluorouracil. For the first class of binding, N=(54.0±0.3), ⊿H⁰=(30.0±0.4) kJ·mol^-1 (endothermal), ⊿S⁰=(196.0±2.6) J·mol-1·K^-1 (entropy increasing), ⊿G⁰=(-28.4±0.3) kJ·mol^-1; for the second class of binding, N=(77.0±0.4), ⊿H⁰=(-20.0±0.4) kJ·mol^-1 (exothermal), ⊿S⁰=(28.6±0.3) J·mol^-1·K^-1 (entropy increasing), ⊿G⁰=(-28.5±0.2) kJ·mol ^-1. The interactions between 5-fluorouracil and BSA induced the relative contents of secondary structure units of protein (BSA) to change in two classes of binding processes.

Key words: 5-fluorouracil, Bovine serum albumin, Isothermal titration calorimetry, Circular dichroism spectra