Open AccessPumping capacity of bacterial reaction centers and backpressure regulation of energy transduction
Author(s) -
van Rotterdam Bart J.,
Westerhoff Hans V.,
Visschers Ronald W.,
Bloch Dimitri A.,
Hellingwerf Klaas J.,
Jones Michael R.,
Crielaard Wim
Publication year - 2001
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.2001.01951.x
Subject(s) - rhodobacter sphaeroides , photosynthetic reaction centre , proton coupled electron transfer , chemistry , proton , chemiosmosis , electron transfer , histidine , membrane , electron transport chain , membrane potential , photochemistry , biophysics , photosynthesis , amino acid , biochemistry , atp synthase , physics , quantum mechanics , biology , enzyme
Transduction of free‐energy by Rhodobacter sphaeroides reaction‐center‐light‐harvesting‐complex‐1 (RCLH1) was quantified. RCLH1 complexes were reconstituted into liposomal membranes. The capacity of the RCLH1 complex to build up a proton motive force was examined at a range of incident light intensities, and induced proton permeabilities, in the presence of artificial electron donors and acceptors. Experiments were also performed with RCLH1 complexes in which the midpoint potential of the reaction center primary donor was modified over an 85‐mV range by replacement of the tyrosine residue at the M210 position of the reaction center protein by histidine, phenylalanine, leucine or tryptophan. The intrinsic driving force with which the reaction center pumped protons tended to decrease as the midpoint potential of the primary donor was increased. This observation is discussed in terms of the control of the energetics of the first steps in light‐driven electron transfer on the thermodynamic efficiency of the bacterial photosynthetic process. The light intensity at which half of the maximal proton motive force was generated, increased with increasing proton permeability of the membrane. This presents the first direct evidence for so‐called backpressure control exerted by the proton motive force on steady‐state cyclic electron transfer through and coupled proton pumping by the bacterial reaction center.