Chirascan plus qcd instrument

All experiments on CytR and PurR were recorded in freshly prepared, filtered and degassed 20 mM sodium phosphate buffer at pH 7.0 without or with urea, unless mentioned otherwise. Protein solutions were routinely filtered through 0.22 μm syringe filters before every experiment. Far-UV and near-UV circular dichroism (CD) spectra were recorded in a Jasco J-815 spectropolarimeter connected to a Peltier system at a concentration of ∼25 and ∼100 μM, respectively. The urea melts in the range of 0 to 6–8 M urea were recorded at 298 K under the same buffer conditions as above. The fluorescence experiments were performed in a Chirascan Plus qCD instrument (Applied Photophysics Ltd., UK) by exciting ∼26 μM of CytR in 10 × 10 mm pathlength cuvette at 274 nm and collecting the spectra between 280 and 400 nm. The quantum yields were estimated employing NATA as a reference (0.13 at 298 K in water).