Objective: Surfactin, a crystalline peptide lipid surfactant produced by Bacillus subtilis, inhibits fibrin clot formation. Human Serum Albumin (HSA) is the most abundant protein in the circulatory system. Its principal function is to transport a great variety of metabolites and drugs such as anticoagulants. In the present work, the interaction of HAS with surfactin in solution as a function of concentration is reported. Materials and methods: The structure of HSA at different pH values in the absence and presence of surfactin was investigated by fluorescence and circular dichroism (CD) spectroscopies. The different effects of surf actin upon binding to HSA are interpreted based on considerations of the expected changes in the vicinity of tryptophan residue W214. Results: The results of fluorescence and CD showed that HSA partially unfolded at pH 3.0 and 10.0 in comparison with pH 7.0. At pH 7.0 and 10.0, surf actin at low concentrations caused a red shift of maximum emission and at high concentrations a blue shift of maximum emission, which should mean unfolding after partial folding. But, compare with other pH values (pH 7.0 and 10.0), in pH 3.0, surf actin does not have considerable effect. Stability of HSA obtained at pH 7.0 and 10.0. ?G (H2O) was about 15 kJmol-1 at pH 7.0 and pH 10.0. Conclusion: Surfactin can denature HSA at very low concentration (0.01 mM). This effect is very similar to synthetic anionic surfactants such as sodium dodecyl sulfate.

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