Suggestion of existence of two forms of halorhodospin in alkaline solution.

Illumination of halorhodopsin (hR590) with orange light in alkaline solution produced a 410 nm absorbing species (hR410), which returned to hR590 upon blue light illumination. The amount of the flash-reactive species of hR590 was estimated by the flash-yield. Illumination with orange light decreased the flash yield, due to the formation of hR410. Blue light illumination of this sample led to the increase of the yield, which was larger than that before orange light illumination. In dark, the yield decreased gradually in 3-4 days. The scheme is proposed in which there exist two forms of hR590.