Many different techniques are used currently to obtain a perfectly characterized, controlled and stabilized protein based drug. Amongst them calorimetry provides experimental data with a critical importance for the effect of the temperature on the unfolding and aggregation of proteins.
The microcalorimetry technique was used to study the unfolding and aggregation effects occurring in aqueous solutions of proteins. Simple data observation and comparison allows determining the most stabilizing formulation conditions, even in cases involving complex blends.
The thermally induced structural modifications of a protein do not only depend of its origin and extraction, purification conditions, but also of its environmental conditions like pH, salt content, or solvent type. The impact of formulation on the unfolding of RNase A was tested under different conditions. Tm temperature shifts to lower values in a presence of urea.
The β-lactoglobulin stability and aggregation was studied at different concentration, acidity and amount of NaCl. At pH 4 the protein is stabilized by adding sodium chloride. At neutral pH the mechanism is more complex and endothermic thermal effects are detected at high temperatures. They correspond to the depolymerization of the unfolded protein resulting in a formation of smaller peptides. The exothermic effects were attributed to Maillard reaction between the peptides and polysaccharide impurities contained in the material. In the presence of NaCl, an effect related to the protein aggregation is observed.
Additionally, the results from a thermal stability measurements of different gamma globulin proteins will be presented.