Trans/13-cis isomerization is essential for both the photocycle and proton pumping of bacteriorhodopsin

• Published in: Biophysical journal 1985-04, Vol.47 (4), p.509-512
• Main Authors: Chang, C.H., Govindjee, R., Ebrey, T., Bagley, K.A., Dollinger, G., Eisenstein, L., Marque, J., Roder, H., Vittitow, J., Fang, J.M.
• Format: Article
• Language: English
• Subjects: bacteriorhodopsin; Bacteriorhodopsins - physiology; Bacteriorhodopsins - radiation effects; Biological and medical sciences; Carotenoids - physiology; Cell structures and functions; Chloroplast, photosynthetic membrane and photosynthesis; Fundamental and applied biological sciences. Psychology; Halobacterium; Halobacterium salinarium; Hydrogen-Ion Concentration; Isomerism; Molecular and cellular biology; Photochemistry; photocycles; Photolysis; Protons; purple membranes; Spectrophotometry; Spectrophotometry, Infrared
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(85)83944-8

We studied an analogue of bacteriorhodopsin whose chromophore is based on all-trans retinal. A five-membered ring was built around the 13–14 double bond so as to prohibit trans to 13-cis isomerization. No light-induced photochemical changes were seen, other than those due to a small amount (approximately 5%) of unbleached bacteriorhodopsin remaining in the apomembrane used for regeneration. The techniques used included flash photolysis at room and liquid nitrogen temperatures and Fourier-transform infrared difference spectroscopy. When the trans-fixed pigment was incorporated into phospholipid vesicles, no evidence of light-initiated proton pumping could be found. The results indicate that trans to 13-cis isomerization is essential for the photochemical transformation and function of bacteriorhodopsin.