Photo-bleaching of firefly luciferin with UV irradiation

We quantitatively investigated the photo-bleaching of D-luciferin in aqueous solutions by UV-light irradiation at 325-, 365-, and 405-nm wavelengths. As a function of UV-light irradiation duration, we measured the numbers of undamaged D-luciferin molecules by quantitative bioluminescence experiments. Single-exponential fitting was performed to obtain the photo-bleaching rate per irradiation time, from which we extracted the photo-bleaching cross-sections crB defined as product 0 x crA of the photo-absorption cross-section crA and photo-bleaching quantum yield 0 of photo-excited D-luciferin. crB was about 0.8-4.5 x 10-20 cm2, while crA was about 1.3-6.3 x 10-17 cm2. Our findings showed that 0 is 7 x 10-4 independently of UV-light wavelength.