Abstract
The rates of the primary electron-transfer processes in Rhodobacter sphaeroides reaction centers have been examined in detail by using 150-fs excitation flashes at 870 nm. At room temperature the apparent time constants for both initial charge separation (P* --> P+BPhL-) and subsequent electron transfer (P+BPhL- --> P+QA-) are found to encompass a range of values (approximately 1.3-4 ps and approximately 100-320 ps, respectively), depending on the wavelength at which the kinetics are followed. We suggest this reflects a distribution of reaction centers (or a few conformers), having differences in factors such as distances or orientations between the cofactors, hydrogen bonding, or other pigment-protein interactions. We also suggest that the time constants observed at cryogenic temperatures (approximately 1.3 and approximately 100 ps, respectively, with much smaller or negligible variation with detection wavelength) do not reflect an actual increase in the rates with decreasing temperature but rather derive from a shift in the distribution of reaction centers toward those in which electron transfer inherently occurs with the faster rates.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Allen J. P., Feher G., Yeates T. O., Rees D. C., Deisenhofer J., Michel H., Huber R. Structural homology of reaction centers from Rhodopseudomonas sphaeroides and Rhodopseudomonas viridis as determined by x-ray diffraction. Proc Natl Acad Sci U S A. 1986 Nov;83(22):8589–8593. doi: 10.1073/pnas.83.22.8589. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Austin R. H., Beeson K. W., Eisenstein L., Frauenfelder H., Gunsalus I. C. Dynamics of ligand binding to myoglobin. Biochemistry. 1975 Dec 2;14(24):5355–5373. doi: 10.1021/bi00695a021. [DOI] [PubMed] [Google Scholar]
- Chang C. H., Tiede D., Tang J., Smith U., Norris J., Schiffer M. Structure of Rhodopseudomonas sphaeroides R-26 reaction center. FEBS Lett. 1986 Sep 1;205(1):82–86. doi: 10.1016/0014-5793(86)80870-5. [DOI] [PubMed] [Google Scholar]
- Frauenfelder H., Hartmann H., Karplus M., Kuntz I. D., Jr, Kuriyan J., Parak F., Petsko G. A., Ringe D., Tilton R. F., Jr, Connolly M. L. Thermal expansion of a protein. Biochemistry. 1987 Jan 13;26(1):254–261. doi: 10.1021/bi00375a035. [DOI] [PubMed] [Google Scholar]
- Kleinfeld D., Okamura M. Y., Feher G. Electron-transfer kinetics in photosynthetic reaction centers cooled to cryogenic temperatures in the charge-separated state: evidence for light-induced structural changes. Biochemistry. 1984 Nov 20;23(24):5780–5786. doi: 10.1021/bi00319a017. [DOI] [PubMed] [Google Scholar]
- Martin J. L., Breton J., Hoff A. J., Migus A., Antonetti A. Femtosecond spectroscopy of electron transfer in the reaction center of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26: Direct electron transfer from the dimeric bacteriochlorophyll primary donor to the bacteriopheophytin acceptor with a time constant of 2.8 +/- 0.2 psec. Proc Natl Acad Sci U S A. 1986 Feb;83(4):957–961. doi: 10.1073/pnas.83.4.957. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Woodbury N. W., Becker M., Middendorf D., Parson W. W. Picosecond kinetics of the initial photochemical electron-transfer reaction in bacterial photosynthetic reaction centers. Biochemistry. 1985 Dec 17;24(26):7516–7521. doi: 10.1021/bi00347a002. [DOI] [PubMed] [Google Scholar]