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Reaction cycle and thermodynamics in bacteriorhodopsinLight causes the all-trans to 13-cis isomerization of the retinal in bacteriorhodopsin; the thermal relaxation leading back to the initial state drives proton transport first via proton transfer between the retinal Schiff base and D85 and then between the Schiff base and D96. The reaction sequence and thermodynamics of this photocycle are described by measuring time-resolved absorption changes with a gated multichannel analyzer between 100 ns and 100 ms, at six temperatures between 5 degrees C and 30 degrees C. Analysis of the energetics of the chromophore reaction sequence is on the basis of a recently proposed model (Varo & Lanyi, Biochemistry 30, 5016-5022, 1991) which consists of a single cycle and many reversible reactions: BR -hv-->K<==>L<==>M1-->M2<==>N<==>O-->BR. The existence of the M1-->M2 reaction, which functions as the switch in the proton transfer, is confirmed by spectroscopic evidence. The calculated thermodynamic parameters indicate that the exchange of free energy between the protein and the protons is at the switch step. Further, a large entropy decrease at this reaction suggests a protein conformation change which will conserve delta G for driving the completion of the reaction cycle. The results provide insights to mechanism and energy coupling in this system, with possible relevance to the general question of how ion pumps function.
Document ID
20050000820
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Lanyi, J. K.
(University of California Irvine 92717)
Date Acquired
August 22, 2013
Publication Date
January 1, 1992
Publication Information
Publication: Acta physiologica Scandinavica. Supplementum
Volume: 607
ISSN: 0302-2994
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
Review
Review, Tutorial
NASA Discipline Exobiology
Non-NASA Center

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