Dansylation of Streptomyces subtilisin inhibitor: spectrometric analysis of the fluorescence-labeled inhibitor

Specific labeling of tyrosine residues of Streptomyces subtilisin inhibitor (SSI) was carried out by dansyl chloride. Analysis revealed that two tyrosine residues out of three in SSI were modified. The resulting fluorescent SSI was fully active as a subtilisin inhibitor. Fluorescence spectra of the modified SSI were investigated. Efficiency of energy transfer from intrinsic tryptophan residues of SSI to the introduced dansyl residue was found to be influenced by the complex formation of SSI with subtilisin.