Photoswitching of the chromophore in cerFP505.

A) Absorption spectra after irradiation with 400 nm (on-state) or with 450 nm light (off-state). Deactivation gives rise to a second peak around 390 nm. B) Ground state equilibrium. Irradiation at 400 nm drives the protein to the on-state, 450 nm light turns off the “activatable” fraction of the protein. Bars above the x-axis specify the light treatment, 400 nm light (white bar), 450 nm light (grey bar) or no light (black bar). C) Fluorescence emission of the protein in the on- or off-state was recorded for ≥30 min in the dark after 5 min irradiation with 400 or 450 nm light. Bars above the x-axis specify the light treatment as described above. D) The reversibility of the reaction is shown for eight cycles of activation/deactivation. Bars above the x-axis specify the light treatment as described in (B).