Primary photophysics of the FMN binding LOV2 domain of the plant blue light receptor phototropin of Avena sativa

Abstract The temporal evolution of the initially excited singlet state of flavine mononucleotide, which is the cofactor in the LOV2 domain of the blue photoreceptor phototropin, has been studied in picosecond time-resolved fluorescence and femtosecond time-resolved absorption experiments. In the LOV2-WT protein of Avena sativa singlet–triplet intersystem crossing proceeding within 2.3 ns is the primary process which increases the triplet yield by a factor of 1.23 as compared to a mutant where cysteine 39 is replaced by alanine. This flavin triplet state is responsible for the formation of a cysteinyl–flavin adduct which triggers the unique photocycle of the LOV2 domain and thus the sensoric function of the blue light receptor phototropin.