There are four types of retinal proteins in the membrane of Halobacterium salinarum. Bacteriorhodopsin (BR) and halorhodopsin (HR) convert light energy into electrostatic gradients that can be used by the cell as an energy source to produce ATP. Sensory rhodopsin I (SR I) and phoborhodopsin (pR) enable the cells to migrate toward an environment optimal for light energy harvesting while avoiding potentially damaging shorter wavelength light. In the present work, low temperature photoreaction cycle of pR expressed in E. coli was studied. Comparing to the previous results, the new findings in the present work are: (i) The K-like intermediate was found to be a mixture of two photoproducts. (ii) Formation of an L-like intermediate (P482) was observed. (iii) Upon light irradiation, formation of a long lived shorter wavelength photoproduct (P370) was observed at 20 ℃.
Low-temperature photoreaction cycle of phoborhodopsin (sensory rhodopsin II) from Halobacterium salinarium
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