Trans/13-cis isomerization is essential for both the photocycle and proton pumping of bacteriorhodopsin.
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.
Chang
C H
CH
Govindjee
R
R
Ebrey
T
T
Bagley
K A
KA
Dollinger
G
G
Eisenstein
L
L
Marque
J
J
Roder
H
H
Vittitow
J
J
Fang
J M
JM
D001436:Bacteriorhodopsins / Q000502:physiology* / Q000528:radiation effects; D002338:Carotenoids / Q000502:physiology*; D006217:Halobacterium; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D010777:Photochemistry; D010782:Photolysis; D011522:Protons; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared
D011522:Protons; D002338:Carotenoids; D001436:Bacteriorhodopsins