Human serum transferrin is the major iron transport protein in human organisms. Iron bound to transferrin is transported from the digestive system to cells that require iron. A change in the pH causes the release of iron from transferrin. Transferrin has two iron binding sites that require the presence of the synergistic anion. The most common glycoform of transferrin in healthy humans consists of two biantennary oligosaccharide chains that together contain four sialic acids with carbonate as synergistic anion. Other structurally similar carboxylic ions such as oxalate have shown to act as synergistic anions in vitro. Chronic alcoholic disease, inflammatory diseases and sepsis can cause desialylation of transferrin, and hyperoxaluria or gastrointestinal diseases can lead to higher serum oxalate levels. The aim of this thesis was to determine thermodynamic parameters for the binding of Fe in the form of FeNTA to transferrin with different sialylation index, and in the presence of carbonate and oxalate as synergistic anions. Commercially available native human serum transferrin was used as sialylated transferrin, while the desialylated transferrin was prepared in in vitro using neuraminidase enzyme. After 99% reduction in sialic acid content was confirmed, thermodynamic parameters were determined using isothermal titration calorimetry. Our data have shown that in binding sites differ in both kinetics and thermodynamics of the binding. Moreover, it was discovered that desialylation affects thermodynamic parameters of the iron binding in the form of FeNTA to transferrin, leading to a shift towards exothermic binding enthalpies. Furthermore, in the presence of carbonate at concentrations corresponding to those in human serum, the binding constant increases. These findings are in support of the possible connection between the desialylation and sequestration as an organism’s response to pathogen infections. In addition to desialylation, oxalate as a synergistic anion in in vitro conditions also increases the binding constant of iron to transferrin, and the binding becomes more exergonic. Together with the stronger prebinding constants of oxalate to human serum transferrin, the above provides the basis for the possible formation of the Fe-oxalate-Tf ternary complex in in vivo conditions, especially in conditions with increased concentration of oxalate.