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Biophys. J. BioFAST: First Published February 10, 2006. doi:10.1529/biophysj.105.077883
© 2006 by the Biophysical Society.

A more recent version of this article appeared on May 1, 2006.
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BIOENERGETICS

Protein-cofactor Interactions in Bacterial Reaction Centers from Rb. Sphaeroides R-26: I. Identification of the ENDOR Lines Associated with the Hydrogen Bonds to the Primary Quinone QA•-

Marco Flores 1, Roger A. Isaacson 2, Edward Abresch 2, Rafael Calvo 3, Wolfgang Lubitz 4 and George Feher 5*

1 UC San Diego; Max-Planck-Institut fuer Strahlenchemie
2 Univ. of California - San Diego
3 UNL & INTEC (CONICET-UNL)
4 Max-Planck-Institut fuer Strahlenchemie
5 UC San Diego

* To whom correspondence should be addressed. E-mail: gfeher{at}ucsd.edu.

Submitted on November 16, 2005
Revised on December 27, 2005
Accepted on 18 January 2006


  Abstract
Hydrogen bonds are important in determining the structure and function of biomolecules. Of particular interest are hydrogen bonds to quinones, which play an important role in the bioenergetics of respiration and photosynthesis. In this work we investigated the hydrogen bonds to the two carbonyl oxygens of the semiquinone QA•- in the well characterized reaction center (RC) from the photosynthetic bacterium Rb. sphaeroides R-26. We used EPR and ENDOR techniques at 35 GHz at a temperature of 80 K. The goal of this study was to identify and assign sets of 1H-ENDOR lines to protons hydrogen bonded to each of the two oxygens. This was accomplished by preferentially exchanging the hydrogen bond on one of the oxygens with deuterium while concomitantly monitoring the changes in the amplitudes of the 1H-ENDOR lines. The preferential deuteration of one of the oxygens was made possible by the different 1H -> 2H exchange times of the protons bonded to the two oxygens. The assignment of the 1H-ENDOR lines sets the stage for the determination of the geometries of the H-bonds by a detailed field selection ENDOR study to be presented in a future paper.

Key Words: Assignment of ENDOR lines, Bacterial Photosynthesis, Proton exchange times, Semiquinone radical




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M. Flores, R. Isaacson, E. Abresch, R. Calvo, W. Lubitz, and G. Feher
Protein-Cofactor Interactions in Bacterial Reaction Centers from Rhodobacter sphaeroides R-26: II. Geometry of the Hydrogen Bonds to the Primary Quinone Formula by 1H and 2H ENDOR Spectroscopy
Biophys. J., January 15, 2007; 92(2): 671 - 682.
[Abstract] [Full Text] [PDF]


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Copyright © 2006 by the Biophysical Society.