Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1249758 | Vibrational Spectroscopy | 2008 | 9 Pages |
Abstract
Rapid-scan FTIR difference spectroscopy was used to investigate proton and electron transfer reactions in photosynthetic reaction centers from Rhodobacter sphaeroides. Experiments at different temperatures and in the presence of D2O have provided strong indication that a transient band at 1707 cmâ1 previously identified after both the 1st and the 2nd flashes [A. Mezzetti, W. Leibl, Eur. Biophys. J. 34 (2005) 921] is given by a transient protonation of the side chain of a Asp or Glu residue situated on the proton transfer pathway from the cytoplasm to the QB site. Experiments in D2O on a Asp-M17 â Asn mutant reaction center, where the proton and electron transfer reactions are slowed down compared to the wild-type, showed that the kinetic isotope effect induced by H/D exchange slows down the electron transfer reaction after the 1st flash, confirming the strong coupling between proton and electron transfer. Rapid-scan FTIR experiments on Cd2+-treated reaction centers, in agreement with previous UV-vis measurements [P. Adelroth, M.L. Paddock, L.B. Sagle, G. Feher, M.Y. Okamura, Proc. Natl. Acad. Sci. U.S.A. 97 (2000) 13086], showed that upon addition of Cd2+, which inhibits proton uptake, the QAâQB â QAQBâ reaction is slowed. Interestingly, the transient 1707 cmâ1 band is not visible in the first spectrum recorded early after the flash. This strongly suggests its identification with a residue situated on the proton transfer pathway, which is perturbed upon metal cation binding.
Related Topics
Physical Sciences and Engineering
Chemistry
Analytical Chemistry
Authors
Alberto Mezzetti, Winfried Leibl,