Binding properties of adenosine deaminase interacted with theophylline

Abstract

Thermodynamic studies were carried out to evaluate the binding of theophylline on adenosine deaminase (ADA) in 50mM sodium phosphate buffer pH 7.5, at 300 K, using isothermal titration calorimetry (ITC). A simple method for determination of binding isotherm in the drug-ADA interaction was applied using ITC data. ADA has two binding sites for theophylline, which show positive cooperativity in its sites. The intrinsic association equilibrium constants are 6 and 52mM-1 in the first and second binding sites, respectively. Hence, occupation of the first site has produced an appreciable enhancement by 8.7 of the binding affinity of the second site. The molar enthalpies of binding are -12.2 and -14.9 kJ/mol in the first and second binding sites, respectively. © 2004 Pharmaceutical Society of Japan.