Blue light regeneration of bacteriorhodopsin bleached by continuous light

Photobleaching of bacteriorhodopsin (BR) by continuous light has recently been demonstrated. This bleaching consists of at least two subsequent product states. One of them is absorbing maximally in the blue spectral region. Our present study shows that upon illumination of the bleached sample with blue light a back photoprocess appears, resulting in regeneration of the original BR state. From a technical point of view, the observed phenomenon is similar to the reverting effect of blue light on the photocycle. An important difference is that the photobleached state of BR is much more stable than any of the photocycle intermediates, and may provide an advantage for several technical applications.