(Mechanism of proton pumping by bacteriorhodopsin)
Two methods were used to test the hypothesis that proteolysis of the C-terminal tail of bacteriorhodopsin affects the quantum efficiency of proton pumping. An apparent good correlation was found between the amount of the slowly decaying forms of the M intermediate and the number of protons pumped. This also suggests that the photocycle may contain M (fast) and M (slow) in different branches. Using artificial analogues of bacteriorhodopsin, the ring portion of the retinal was shown not to be an important factor in determining the photochemical and proton pumping properties of the artificial pigments, but that modification of the chain is. At least four double bonds along the chain are necessary for efficient proton pumping. The purple membrane normally contains several different cations tightly bound and it was shown that removal of these cations changes the color of the membrane from purple to blue. We proposed that cations acted by modulation of the surface potential and hence the local proton concentration near the membrane. A new intermediate was found in the bacteriorhodopsin photocycle, R. This new intermediate can explain several quite perplexing observations that have been made about the photocycle. The conformation of the retinal of the third rhodopsin-like pigment in Halobacteria, sensory rhodopsin, is all-trans and that light isomerizes the chromophore to the 13-cis conformation. 26 refs.
- Research Organization:
- Illinois Univ., Urbana (USA)
- DOE Contract Number:
- AC02-82ER12087
- OSTI ID:
- 6387237
- Report Number(s):
- DOE/ER/12087-T4; ON: DE87012299
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
550200 -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
AMINO ACID SEQUENCE
BIOCHEMICAL REACTION KINETICS
CATIONS
CHARGED PARTICLES
HYDROGEN IONS
HYDROGEN IONS 1 PLUS
IONS
KINETICS
MEMBRANE TRANSPORT
MEMBRANES
MOLECULAR STRUCTURE
ORGANIC COMPOUNDS
PHOTOSYNTHETIC MEMBRANES
PIGMENTS
PROTEINS
REACTION KINETICS
RHODOPSIN
STRUCTURE-ACTIVITY RELATIONSHIPS
VITAMIN A
VITAMINS