Fluorescence of tryptophan in the denaturation of human serum albumin under the action of sodium dodecyl sulfate

Tryptophan fluorescence of human serum albumin (HSA) when sodium dodecyl sulfate (SDS) was added to a solution of the protein was studied at various pH values, which allowed us to get an idea about the mechanism of the denaturation of HSA under the action of SDS. The two-stage quenching of tryptophan fluorescence of HSA as the concentration of SDS increased was evidence of the two-stage character of denaturation. The first stage involved loosening of protein globules, and the second one was the complete uncoiling of the amino acid protein chain. At solution pH higher than the isoelectric point of the protein (pI 4.7), denaturation stopped at the first stage. At pH values below pI of the protein, the denaturation of the protein under the action of SDS was more effective and deep (involved both stages).