2009 Volume 58 Issue 11 Pages 573-579
The effect of gemini surfactant, sodium dilauramidoglutamide lysine (DLGL), on the secondary structure of bovine serum albumin (BSA) was examined at 25°C and at high temperatures up to 130°C. The helicity (66%) of the protein decreased to 53% in the DLGL solution at 25°C and it also decreased to 16% with rise of temperature. Although approximately half of the original helical structures were destroyed upon heating up to 75°C, most of the structures were maximally protected in the coexistence of 0.30mM DLGL at 75°C (the protein concentration was 0.010mM). At temperatures below 75°C, the protected helicity became maximal at such low DLGL concentrations. In the thermal denaturations above 80°C, the protective effect did not appear at low DLGL concentrations, but monotonously enlarged with the surfactant concentration. On the other hand, upon cooling to 25°C after the thermal denaturations below 75°C, the helicity was maximally recovered to about 60% in the presence of DLGL below 0.30mM. Upon cooling to 25°C from high temperatures above 85°C, the recovered helicity gradually increased with the surfactant concentration. The present novel effect, especially observed at low DLGL concentrations, might be fulfilled by the monomer ions of the gemini surfactant, since actual binding numbers of DLGL onto BSA are necessarily smaller than the mixing ratios around 30mol/mol.