Protective Effect of Gemini Surfactant on Secondary Structural Change of Bovine Serum Albumin in Thermal Denaturation up to 130.DEG.C

The effect of gemini surfactant, sodium dilauramidoglutamide lysine (DLGL), on the secondary structure of bovine serum albumin (BSA) was examined at 25 degrees C and at high temperatures up to 130 degrees C. The helicity (66%) of the protein decreased to 53% in the DLGL solution at 25 degrees 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 degrees C, most of the structures were maximally protected in the coexistence of 0.30 mM DLGL at 75 degrees C (the protein concentration was 0.010 mM). At temperatures below 75 degrees C, the protected helicity became maximal at such low DLGL concentrations. In the thermal denaturations above 80 degrees 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 degrees C after the thermal denaturations below 75 degrees C, the helicity was maximally recovered to about 60% in the presence of DLGL below 0.30 mM. Upon cooling to 25 degrees C from high temperatures above 85 degrees 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 30 mol/mol.