Interaction of gallium maltolate with apotransferrin: A spectroscopic and isothermal titration calorimetric study

The interaction of gallium maltolate (Ga(ma) 3 ) with human serum transferrin has been investigated by means of UV–Vis spectroscopy and isothermal titration calorimetry. First, the values of the first and second associative stepwise binding constants of Ga(ma) 3 to apotransferrin were estimated by use of a data analyzing method. The synergistic role of the carbonate anion in the formation of gallium-transferrin bonds was also investigated. Experimental results indicated that the extent of binding is maximum at physiological pH. Citrate ion and transferrin have a competitive behavior toward gallium binding. By use of the calorimetric results, the values of 23.44 and 8.99 kJ mol −1 were determined for the associative stepwise enthalpy changes. This represents the endothermic entropy-driven nature of the process.