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Bacteriorhodopsin D85N: three spectroscopic species in equilibrium
G J Turner1, L J Miercke, T E Thorgeirsson
1Department of Biochemistry & Biophysics, University of California, San Francisco 94143.
Biochemistry
|February 9, 1993
Summary
Bacteriorhodopsin (BR) with D85N mutation exhibits three equilibrium states, mimicking wild-type BR photocycle intermediates. This provides a model for studying BR
Area of Science:
- Biophysics
- Photochemistry
- Structural Biology
Background:
- Bacteriorhodopsin (BR) is a light-driven proton pump crucial for cellular energy generation.
- Understanding the photocycle intermediates of BR is key to elucidating its mechanism.
- The D85N mutation in BR alters its photocycle dynamics and spectral properties.
Purpose of the Study:
- To characterize the ground-state equilibrium chromophoric states of D85N bacteriorhodopsin.
- To compare these states with the photointermediates of wild-type BR.
- To validate D85N BR as a model for studying the latter stages of the BR photocycle.
Main Methods:
- Ground-state absorbance spectroscopy.
- pH-dependent spectral analysis.
- Retinal isomer analysis.
Main Results:
- D85N BR exists in three distinct equilibrium chromophoric states.
- These states spectrally resemble wild-type BR intermediates M, N, and O.
- The pH dependence of these states mirrors that of wild-type BR photocycle intermediates.
- The M-like state features a deprotonated Schiff base and 13-cis retinal.
- The O-like state is dominated by the all-trans retinal isomer.
Conclusions:
- The D85N BR equilibrium system serves as a valuable model for the M, N, and O intermediates of the wild-type BR photocycle.
- These findings support kinetic models highlighting the significance of back-reactions in the BR photocycle.
- Characterization provides insights into molecular transitions within the BR photocycle.