Dynamics Surrounding Cys-34 in Native, Chemically Denatured, and Silica-Adsorbed Bovine Serum Albumin

We report the steady-state and time-resolved fluorescence of 6-acryloyl(dimethylamino)naphthalene (acrylodan) covalently attached to Cys-34 in bovine serum albumin (BSA). For this conceptually simple system, complicated fluorescence intensity and anisotropy decay kinetics are observed. The steady-state and time-resolved results demonstrate the presence of an excited-state reaction for the BSA—acrylodan system. Additional analysis shows that dipolar relaxation of the environment surrounding acrylodan within BSA is responsible for most of the observed time-dependent evolution of the emission spectrum. The effects of temperature, chemical denaturation, and protein adsorption to a bare silica substrate are also investigated, These results demonstrate the complexity of the changes within a protein/biorecognition element that affect the signal from a single fluorescent reporter group.