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Both putative blue-light photoreceptors from Arabidopsis thaliana and Sinapis alba were found to contain methenyltetrahydrofolate and flavin adenine dinucleotide, presumably in the two-electron-reduced form. This indicates that the blue light photoreceptor may initiate signal transduction by a novel pathway involving electron transfer. Both photoreceptors, however, do not have any photoreactivating activity despite a high degree of sequence homology to DNA photolyase.

The vibrational changes occurring in the full-length Arabidopsis cryptochrome 1 (CRY 1) protein upon illumination with blue light are investigated by Fourier transform infrared (FTIR) and ultraviolet (UV)/vis difference spectroscopy. The reversible formation of a neutral flavin radical by blue light is accompanied by changes in secondary structure of the apoprotein and this analysis is useful for FTIR studies on flavoprotein radicals in general and will facilitate future work on the cryptochrome signaling process.