A comparative study on specific and nonspecific interactions in bovine serum albumin: thermal and volume effects of halothane and palmitic acid

Interaction modes of halothane and palmitic acid with bovine serum albumin (BSA) were studied from the thermal and volumetric viewpoints. The thermal stability of BSA was increased by increasing both ligand concentrations. However, the stronger effect of palmitic acid than halothane on BSA was observed at lower concentrations irrespective of the pH-dependent BSA structure. On the other hand, the volume of BSA in the solution shrunk by adding halothane independent of its structure while it expanded by adding palmitic acid. The molar ratio of halothane to BSA at the effective concentration was not consistent with the binding numbers on human serum albumin determined from the X-ray analysis, whereas that of palmitic acid was in good agreement with the numbers. We judged from these facts that halothane is a nonspecific binder to BSA; by contrast, palmitic acid is a specific binder. The stabilization mechanisms of the BSA structure were also revealed.