INFLUENCE OF ALKYLUREAS ON THE FLUORESCENCE PROPERTIES OF MODEL DIPEPTIDES AND RIBONUCLEASE A

Nataša Poklar, Aleksandra Mecilošek and Gorazd Vesnaver Department of Chemistry, University of Ljubljana, Aškerèeva 5, 1000 Ljubljana, Slovenia

ABSTRACT

The influence of guanidinium hydrochloride (GuHCl), urea and some alkylureas on the stability of bovine ribonuclease A (RNase A) in aqueous solutions at 25 ^oC was investigated by measuring the protein intrinsic fluorescence emission as a function of the added denaturant concentration. It was shown that GuHCl is significantly stronger denaturing agent than urea and that in solutions of alkylureas a full RNase A denaturation cannot be achieved even at the highest possible denaturant concentrations. Such behavior was ascribed to lower denaturing efficiency and/or lower solubility of alkylureas. These findings were fully supported by the results of RNase A fluorescence polarization measurements performed in the same denaturant solutions. The fluorescence emission spectra of RNase A were also compared with the corresponding spectra of the model dipeptide containing one tyrosine residue. It was shown that the changes in the RNase A intrinsic fluorescence emission observed at high denaturant concentrations are due primarily to the unfolding of the protein