Fluorescence lifetime distributions report on protein destabilisation in quenching experiments

Tryptophan is the most often investigated intrinsic fluorophore due to its abundance in proteins and its sensitivity to different environmental conditions. Fluorescence quenching is a powerful method to study proteins and acrylamide is a frequently applied quencher in these investigations. Quenching experiments are sometimes distorted by the undesired protein-quencher interactions that can result in a misinterpretation of the results. Here we focused on the identification of the possible side-effects of acrylamide applying fluorescence lifetime measurements. To provide reference data for protein denaturation the fluorescence parameters were also recorded in the presence of different concentrations of guanidine hydrochloride. In circular dichroism experiments we characterized directly the acrylamide effect on the tertiary structure of the proteins. According to the obtained data in experiments with seven tryptophan-containing proteins the full width at half maximum (FWHM) of the fluorescence lifetime distribution is an appropriate parameter to monitor the undesired effects of acrylamide on the proteins.