BLUF and LOV are blue-light sensor domains that possess flavin as a common chromophore but exhibit distinct photoreactions. lle66 located in the BLUF domain of a cyanobacterial photosensor protein, TePixD, was replaced with Cys to mimic the LOV domain. Light-induced Fourier transform infrared spectra of the 166C TePixD showed that a flavin-Cys adduct, typical of the photoinduced intermediates of LOV domains, was formed in the 166C BLUF domain. This result demonstrates that different types of flavin photoreactions can be realized in the same domain if key amino acids are properly arranged near the flavin and the domain structure itself is not a crucial factor to determine the photoreaction type.