The influence of temperature and urea on intrinsic fluorescence of Streptomyces subtilisin inhibitor. A study by fluorescence polarization and quenching.

Intrinsic fluorescence of new microbial protease inhibitor, Streptomyces subtilisin inhibitor was studied by observing fluorescence polarization degree and lifetime in the temperature range 25-81 degrees C. Striking thermal changes in these fluorescence properties of tryptophan residues were observed. The apparent molecular volumes for tryptophan and tyrosine residues in the native form were determined to be 89 and 75 A3, respectively. The fluorescence quenching by Br- or Cs+ was investigated to obtain a microenvironmental information around tryptophan residues both in the native and denatured form. Cs+ quenches the fluorescence slightly stronger than Br-, implying that there is not any distinctive electrostatic interaction between tryptophan residues and their neighborhood.