Protein-cofactor interactions in bacterial reaction centers from Rhodobacter sphaeroides R-26: I. Identification of the ENDOR lines associated with the hydrogen bonds to the primary quinone QA-
FLORES, M; ISAACSON, RA; ABRESCH, EC; RAFAEL CALVO; LUBITZ, W; FEHER, G
Biophysical Society, USA
Lugar: Baltimore; Año: 2006 vol. 90 p. 3356 - 3356
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 and 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 presented in the accompanying paper.