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Mechanism of the binding of 2-(4'-hydroxyphenylazo)benzoic acid to bovine serum albumin
Authors:K Murakami  T Sano  S Tsuchie  T Yasunaga
Affiliation:1. Department of Chemistry, Faculty of Science, Yamagushi University, Yoshida 1677-1, Yamaguchi 753 Japan;2. Department of Chemistry, Faculty of Science, Hiroshima University, Higashisenda-machi, Naka-ku, Hiroshima 730, Japan
Abstract:The mechanism of the binding of 2-(4'-hydroxyphenylazo)benzoic acid (HABA) to bovine serum albumin was studied by relaxation methods as well as the binding isotherm using gel chromatography. A single relaxation was observed over a wide range of HABA concentration except at the extremes of high concentration where another slow process was observed. The concentration dependence of the reciprocal relaxation time of the fast process decreased monotonically with increase in concentration of HABA at constant polymer concentration. The data were analyzed on the basis of Brown's domain structure model and were found to be consistent with a sequential binding mechanism. The azohydrazon tautomerism of HABA was identified with the intramolecular step of the complex. The activation parameters of the step, determined from the temperature dependence of the relaxation time of the fast process, showed that this step is rate limited by an enthalpy barrier in both forward and backward directions. Comparison of the activation parameters with those of other serum albumin-ligand systems suggests that there is an enthalpy-entropy compensation in the activation process of the intramolecular step with the compensation temperature at about 270 K; the enthalpy-entropy compensation is thought to be related to the hydrophobic nature of the ligand.
Keywords:Bovine serum albumin  Relaxation method  Sequential binding  HABA, 2-(4′-hydroxyphenylazo)benzoic acid  BSA, bovine serum albumin  HSA, human serum albumin  To whom correspondence should be addressed.
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