Polarized fluorescence in the study of rotational diffusion of human albumin during denaturation under the action of SDS

Polarized tryptophan fluorescence of human serum albumin (HSA) was analyzed to determine the parameters of rotational diffusion (rotational relaxation time, rotational diffusion coefficient, and the effective Einstein radius) of HSA molecules during denaturation under the action of sodium dodecyl sulfate (SDS). Two stages of HSA denaturation under the action of SDS were shown: (1) loosening of protein globules and (2) unfolding of the amino-acid chain of the protein. HSA denaturation under the action of SDS is a two-stage process at pH values lower than the pI of HAS but passes through stage 1 only at pH values higher than the pI.