Protective Effect of Biological Osmolytes against Heat- and Chaotropic Agent-Induced Denaturation of Bacillus licheniformis ��-Glutamyl Transpeptidase

In the present study, the stabilizing effect of four different biological osmolytes on Bacillus licheniformis γ-glutamyl transpeptidase ( Bl GGT) was investigated. Bl GGT appeared to be stable under temperatures below 40°C, but the enzyme retained less than 10% of its activity at 60°C. The tested osmolytes exhibited different degrees of effectiveness against temperature inactivation of Bl GGT, and sucrose was found to be the most effective among these. The use of circular dichroism spectroscopy for studying the secondary structure of Bl GGT revealed that the temperature-induced conformational change of the protein molecule could be prevented by the osmolytes. Consistently, the molecular structure of the enzyme was essentially conserved by the osmolytes at elevated temperatures as monitored by fluorescence spectroscopy. Sucrose was further observed to counteract guanidine hydrochloride (GdnHCl)- and urea-induced denaturation of Bl GGT. Taken together, we observed evidently that some well-known biological osmolytes, especially sucrose, make a dominant contribution to the structural stabilization of Bl GTT.