Interaction Between Surfactin and Bovine Serum Albumin

The interaction of surfactin, a typical biosurfactant, with bovine serum albumin (BSA) was investigated by surface tension, fluorescence, freeze-fractured transmission electron microscopy (FF-TEM) and circular dichroism (CD) measurements. The surface tension curves of pure surfactin solution and surfactin/BSA solutions have different phenomena, where two obvious inflections determined as the critical aggregation concentration (cac) and the critical micelle concentration (cmc) appear for surfactin/BSA solutions. The higher BSA concentration, the higher cac and cmc values for surfactin/BSA solution. Fluorescence spectra show that the structure change of BSA is dependent on both surfactin and BSA concentration. The micropolarity, FF-TEM and CD results further demonstrate the interaction between BSA and surfactin. The excess free energy (G(0)) of surfactin/BSA interactions have been obtained as -6.13 and 5.32kJ/mol for 1.0x10(-6) and 3.8x10(-6)mol/L BSA concentration, respectively. The binding ratio (R) determined for surfactin/BSA systems are higher than that reported for dirhamnolipid to BSA. Above all, it can be concluded that the hydrophobic interaction and the hydrogen bonds between surfactin and BSA play the key role for the high binding ratio for surfactin to BAS.