Labeling of Proteins by BODIPY-Quinone Methides utilizing Anti-Kasha Photochemistry

A novel approach for the photolabeling of proteins by a BODIPY fluorophore is reported that is based on an anti-Kasha photochemi-cal reaction from an upper singlet excited state (Sn) leading to the deamination of the BODIPY quinone methide precursor. On the other hand, the high photochemical stability of the dye upon excita-tion by visible light to S1 allows for the selective fluorescence detection from the dye or dye-protein adduct, without concomitant bleaching or hydrolysis of the protein-dye adduct. Therefore, pho-tolabeling and fluorescence monitoring can be uncoupled by using different excitation wavelengths. Combined theoretical and experi-mental studies by preparative irradiations, fluorescence and laser flash photolysis fully disclose the photophysical properties of the dye and its anti- Kasha photochemical reactivity. The application of the dye was demonstrated on photolabeling of bovine serum albu-min