Amino acids and short peptides do not always stabilize globular proteins: A differential scanning calorimetric study on their interactions with bovine α-lactalbumin

Abstract

Amino acids and related compounds have been shown to confer stabilization to proteins; however, the generalization of such a statement is far from reality as there is a lack of experimental data on the interactions of amino acids and short peptides with different proteins. In particular, there are only a few reports1–3 on direct differential calorimetric studies on these systems. Using DSC, we have studied the thermal denaturation of bovine α-lactalbumin in the presence of glycine, alanine, leucine, lysine, aspartic acid, glutamic acid, diglycine, triglycine, tetraglycine, pentaglycine, glycyl-leucine and glycyl-glycyl-leucine at neutral pH. It has been observed that these amino acids and peptides either do not provide thermal stabilization to α-lactalbumin or that the extent of stabilization is negligibly small. However, sucrose was able to confer thermal stability at neutral pH. All the thermal denaturations were found to be two-state (i.e. natureddenatured) and reversible and provide quantitative thermodynamic parameters associated with them. The results have been interpreted in terms of a fine balance between the preferential exclusion and binding which takes place during the course of the denaturation reaction. It follows from this study that the amino acids and peptides do not always stabilize globular proteins.