Bleaching of bacteriorhodopsin by continuous light

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Abstract
A new two step photobleaching process is observed under continuous illumination of bacteriorhodopsin. This photobleaching is considerable even at physiological temperatures and becomes large at 50–60°C. The photobleaching also increases with increasing pH from 7 to 10. We suggest that the bleaching at its final stage could be due to the dissociation of the retinal and a local thermal denaturation‐like process. These facts may question the generally held belief that BR is a stable protein in vivo for a long period of time. Our results may have relevance also to practical applications of bacteriorhodopsin where the stability of bacteriorhodopsin is a key issue. In certain instances, the use of bacteriorhodopsin may require cooled conditions. Here, we defined the conditions under which bacteriorhodopsin is stable. The permanent photobleaching offers a new way of picture imaging and information input for bacteriorhodopsin‐based optical devices.