Protein interaction: concepts from thermodynamic measurements.

Proteins are biological molecules par excellence. They have evolved as elements of structure, catalysis and control. The conflict between the requirement of structural stability and the requirement of functional specificity and efficiency, under varying environmental conditions in which they are often called upon to function, has been evolutionarily solved by a process of thermodynamic compensation. In the simplest form of thermodynamic compensation the Gibb's free energy change (delta G) of a process occurring under different environmental conditions is kept constant (linear compensation) or allowed to vary slightly (non linear compensation) by compensating a large change in enthalpy (delta H) by an equally (or nearly 80) large change in entropy, delta S. In processes like protein adsorption to surfaces the number of various types of interactions involved is so large that compensatory or augmenting changes in the same type of thermodynamic parameter may occur and complicate the picture. Published data do, however, suggested the occurrence of thermodynamic compensation in protein adsorption. It is pointed out that the simultaneous measurement of two thermodynamic parameters, namely, enthalpy change (delta H), and heat capacity change (delta Cp), under appropriate conditions could often lead to an understanding of the dominant types of forces involved in adsorption.