Interaction of cationic surfactant cethyltrimethylammonium bromide with bovine serum albumin in dependence on pH: A study of tryptophan fluorescence

The interaction of cationic surfactant cethyltrimethylammonium bromide (CTAB) with bovine serum albumin (BSA) at various values of pH has been studied using steady-state non-polarized tryptophan fluorescence of BSA and polarized tryptophan fluorescence of BSA. By analysis of intensity of tryptophan fluorescence of BSA, by analysis of position of maximum of spectrum of BSA tryptophan fluorescence, by analysis of polarization of BSA tryptophan fluorescence the qualitative rearrangements of BSA globules at denaturation under action of CTAB are registered. The estimation of parameters of rotational diffusion of BSA molecules helps one to determine the quantitative changes of size of BSA at CTAB-induced denaturation. It is shown that denaturation of BSA, taking place at interaction of cationic surfactant CTAB with BSA, has one-stage mono-phase character. At interaction of CTAB with BSA the deepest denaturation of BSA is reached at 4 mM CTAB (at pH 3.5–8.0). More intensive denaturation of BSA under action of CTAB takes place at values of pH, higher than the isoelectric point of BSA.