Characterization of the cation binding sites of the purple membrane. Electron spin resonance and flash photolysis studies
The binding of Mn/sup 2 +/ and La/sup 3 +/ to the blue membrane prepared by deionization of the Halobacterium halobium purple membrane has been studied by electron spin resonance (ESR) spectroscopy, visible absorption spectroscopy, and flash photolysis. ESR studies indicated that 10 Mn/sup 2 +/ binding sites are present per bacteriorhodopsin monomer. Five high- and medium-affinity sites, normally occupied by Ca/sup 2 +/ and Mg/sup 2 +/ in the purple membrane, as well as five low-affinity sites were found. Proteolysis and chemical modification experiments indicated that the low-affinity sites are located on the bacteriorhodopsin C-terminal segment, while the high- and medium-affinity sites involve other carboxyl groups of the protein. Competition experiments indicated that La/sup 2 +/ binds much more strongly than Mn/sup 2 +/ to these sites. Visible absorption spectroscopy and flash photolysis experiments indicated that binding of Mn/sup 2 +/ or La/sup 3 +/ regenerates both the purple color and formation of the M/sub 4//sup 12/ intermediate. The effect occurs progressively as cations bind to the high- and medium-affinity sites, bound La/sup 3 +/ being more effective than bound Mn/sup 2 +/. It is suggested that divalent cations support both the purple color and proton-pumping activity by rendering less negative the surface potential of the purple membrane. This process may promote deprotonation of the counterion of the retinal Schiff base and possibly of other functional groups. On the other hand, it is proposed that the inhibitory effect of La/sup 3 +/ is mainly due to binding to a site distinct from those of divalent cations.
- Research Organization:
- Centre d'Etudes Nucleaires de Saclay, Gif-sur-Yvette, France
- OSTI ID:
- 6560465
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:4; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
ABSORPTION SPECTROSCOPY
BIOCONVERSION
BIOPHOTOLYSIS
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CONFIGURATION INTERACTION
DECOMPOSITION
ELECTRON SPIN RESONANCE
IONS
MAGNETIC RESONANCE
MANGANESE COMPOUNDS
MEMBRANES
MOLECULAR BIOLOGY
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PHOTOSYNTHETIC BACTERIA
PHOTOSYNTHETIC MEMBRANES
RESONANCE
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS