Inactivation of trypsin in the presence of xanthene dyes was observed through the irradiation of visible ray, but not observed in the dark. As the substrate for trypsin, rose bengale-bound casein was only 80% effective as compared with untreated casein.
The inactivation under the visible ray was accelerated by the elimination of the air, and was prevented in the atmosphere of oxygen. It was assumed that those xanthene dyes inhibitde the trypsin activity via triplet energy transfer. Since the presence of oxygen was essential for the photo-degradation of tryptophan and histidine by rose bengale, it was suggested that photo-inactivation of trypsin was induced without degradation of amino acid residue in the trypsin molecule.