FTIR SPECTROSCOPY OF THE PHOTOREDUCTION OF THE BACTERIOPHEOPHYTIN ELECTRON-ACCEPTOR IN REACTION CENTERS OF RHODOBACTER-SPHAEROIDES AND RHODOPSEUDOMONAS-VIRIDIS
E. Nabedryk et al., FTIR SPECTROSCOPY OF THE PHOTOREDUCTION OF THE BACTERIOPHEOPHYTIN ELECTRON-ACCEPTOR IN REACTION CENTERS OF RHODOBACTER-SPHAEROIDES AND RHODOPSEUDOMONAS-VIRIDIS, Chemical physics, 194(2-3), 1995, pp. 371-378
The photoreduction of the bacteriopheophytin electron acceptor H-A in
reaction centers from Rbodobacter sphaeroides and Rhodopseudomonas vir
idis has been monitored by light-induced FTIR difference spectroscopy
at 10 degrees C, in the presence of reductant and mediator. The striki
ng similarity of the H-A(-)/H-A spectra obtained for Rb. sphaeroides a
nd Rps. viridis reflects comparable interactions of the bacteriopheoph
ytin electron acceptor with the protein in both reaction centers and i
mplies that the photoreduction of H-A affects conserved amino acid res
idues. The H-A(-)/H-A spectra are interpreted by comparison with model
compound spectra of the anion radicals of bacteriopheophytin a and b,
and by analysis of H-1/H-2 isotope effects. The downshift of the 1677
cm(-1) mode in Rb. sphaeroides (1681 cm(-1) in Rps. viridis) reaction
centers with respect to the model compound is interpreted in terms of
a strongly perturbed 9-keto carbonyl of H-A. This perturbation most p
robably originates from hydrogen bonding to Glu L104. At least part of
the positive signal at 1591 cm(-1) in Rb. sphaeroides and at 1601 cm(
-1) in Rps. viridis is assigned to the 9-keto carbonyl mode of H-A(-).
From H-1/H-2 exchange experiments, it is proposed that the (COOH)-H-1
side chain of Glu L104 contributes to the 1745-1735 cm(-1) spectral r
ange with the corresponding (COOH)-H-2 signal displaced to lower frequ
encies and partly hidden under the 1732 cm(-1) band.