Insight into the effect of glycerol on stability of globular proteins in high protein model system

A model system was established to investigate the effect of glycerol on stability of globular proteins. To study whether protective effect of glycerol is dependent on the nature of protein, four kinds of globular protein were used including a-lactalbumin, beta-lactoglobulin, native lactoferrin and lysozyme. Differential scanning calorimetry (DSC) was used to study the thermal stability of the proteins with glycerol aqueous (0-80% v/v). The results showed that the stability of beta-lactoglobulin and lysozyme (hydrophobicity-dominated proteins) increased with glycerol concentration. However, that of alpha-lactalbumin and lactoferrin (metalloproteins), regardless of the ion-binding state, initially increased and then decreased. Different protective effects were observed beyond 50% (v/v) glycerol concentrations in liquid phase. The secondary structure and tryptophan exposure remained unchanged. In conclusion, the protection of glycerol on protein stability was highly dependent on the nature of proteins.