Proton Uptake by Carboxylic Acid Groups upon Photoreduction of the Secondary Quinone (QB) in Bacterial Reaction Centers from Rhodobacter sphaeroides: FTIR Studies on the Effects of Replacing Glu H173
- 19 September 1998
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 37 (41), 14457-14462
- https://doi.org/10.1021/bi981139d
Abstract
In the photosynthetic reaction center (RC) from Rhodobactersphaeroides, Glu H173, located ∼7 Å from the center of the secondary quinone acceptor QB, is expected to contribute to proton uptake upon QB- formation in response to the movement of an electron in its vicinity. Steady-state FTIR difference spectroscopy provides a method to monitor proton uptake by carboxylic acids upon photochemical changes. The FTIR spectra corresponding to the photoreduction of QB were obtained at pH 7 for RCs containing Glu (native), Gln (EQ H173), or Asp (ED H173) at the H173 site. No new bands were observed in the carboxylic acid region (1770−1700 cm-1) in any of the mutant RCs compared to native RCs. In addition, the positive band at 1728 cm-1, previously assigned to Glu L212 [Nabedryk, E., Breton, J., Hienerwadel, R., Fogel, C., Mäntele, W., Paddock, M. L., and Okamura, M. Y. (1995) Biochemistry 34, 14722−14732], remained present in all of the mutant RCs. This result shows that Glu H173 is not a major contributor to proton uptake upon QB- formation and further strengthens the assignment of the 1728 cm-1 band to Glu L212. An increase in the 1728 cm-1 band was observed in the EQ H173 RCs compared to that of either the ED H173 or native RCs. These changes are consistent with Glu and Asp at H173 remaining ionized in the QB and QB- states. Changes in the absorption regions of the semiquinone and amide or side chain groups in the spectra of the mutant RCs suggest slight changes in the protein structure compared to those of native RCs, which could contribute to the altered kinetics observed in the mutant RCs.Keywords
This publication has 10 references indexed in Scilit:
- Energetics of Electron-Transfer and Protonation Reactions of the Quinones in the Photosynthetic Reaction Center of Rhodopseudomonas viridisBiochemistry, 1998
- Redox FTIR difference spectroscopy using caged electrons reveals contributions of carboxyl groups to the catalytic mechanism of haemcopper oxidasesFEBS Letters, 1996
- Carboxyl group protonation upon reduction of the Paracoccus denitrificans cytochrome c oxidase: direct evidence by FTIR spectroscopyFEBS Letters, 1996
- FTIR spectroscopy shows weak symmetric hydrogen bonding of the QB carbonyl groups in Rhodobacter sphaeroides R26 reaction centresFEBS Letters, 1995
- Electrostatic calculations of amino acid titration and electron transfer, Q-AQB-->QAQ-B, in the reaction centerBiophysical Journal, 1995
- FTIR Spectroscopy of QB Photoreduction in RB. Sphaeroides Reaction Centers: Effects of Site-Directed Replacements at GLU L212, ASP L213, and ASP L210 and of 1H/2H ExchangePublished by Springer Nature ,1995
- Application of FTIR Spectroscopy to the Investigation of Dark Structures and Photoreactions of Visual PigmentsIsrael Journal of Chemistry, 1995
- Application of FTIR Spectroscopy to the Structural Study on the Function of BacteriorhodopsinIsrael Journal of Chemistry, 1995
- Probing the secondary quinone (QB) environment in photosynthetic bacterial reaction centers by light‐induced FTIR difference spectroscopyFEBS Letters, 1991
- Control of photosynthetic membrane assembly in Rhodobacter sphaeroides mediated by puhA and flanking sequencesJournal of Bacteriology, 1989