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. 1987 Jun;51(6):937–946. doi: 10.1016/S0006-3495(87)83421-5

Effects of Nuclear Spin Polarization on Reaction Dynamics in Photosynthetic Bacterial Reaction Centers

Richard A Goldstein, Steven G Boxer
PMCID: PMC1330027  PMID: 19431700

Abstract

Singlet-triplet mixing in the initial radical-pair state, P[unk]I[unk], of photosynthetic bacterial reaction centers is due to the hyperfine mechanism at low magnetic fields and both the hyperfine and Δg mechanisms at high magnetic fields (>1 kG). Since the hyperfine field felt by the electron spins in P[unk]I[unk] is dependent upon the nuclear spin state in each radical, the relative probabilities of charge recombination to the triplet state of the primary electron donor, 3PI, or the ground state, PI, will depend on the nuclear spin configuration. As a result these recombination products will have non-equilibrium distributions of nuclear spin states (nuclear spin polarization). This polarization will persist until the 3PI state decays. In addition, due to unequal nuclear spin relaxation rates in the diamagnetic PI and paramagnetic 3PI states, net polarization of the nuclear spins can result, especially in experiments that involve recycling of the system through the radical-pair state. This net polarization can persist for very long times, especially at low temperatures. Nuclear spin polarization can have consequences on any subsequent process that involves re-formation of the radical-pair state.

Numerical calculations of the nuclear polarization caused by both of these mechanics are presented, including the effect of such polarization on subsequent yields of 3PI, 3PI decay rates, the decay rate of the radical pair, and saturation behavior. The effect of this polarization under certain circumstances can be very dramatic and can explain previously noted discrepancies between experiments and theories that do not include nuclear spin polarization effects. Our analysis suggests new classes of experiments and indicates the need to reinterpret some past experimental results.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Chidsey C. E., Takiff L., Goldstein R. A., Boxer S. G. Effect of magnetic fields on the triplet state lifetime in photosynthetic reaction centers: Evidence for thermal repopulation of the initial radical pair. Proc Natl Acad Sci U S A. 1985 Oct;82(20):6850–6854. doi: 10.1073/pnas.82.20.6850. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Deisenhofer J., Epp O., Miki K., Huber R., Michel H. X-ray structure analysis of a membrane protein complex. Electron density map at 3 A resolution and a model of the chromophores of the photosynthetic reaction center from Rhodopseudomonas viridis. J Mol Biol. 1984 Dec 5;180(2):385–398. doi: 10.1016/s0022-2836(84)80011-x. [DOI] [PubMed] [Google Scholar]
  3. Haberkorn R., Michel-Beyerle M. E. On the mechanism of magnetic field effects in bacterial photosynthesis. Biophys J. 1979 Jun;26(3):489–498. doi: 10.1016/S0006-3495(79)85266-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Kaufmann K. J., Dutton P. L., Netzel T. L., Leigh J. S., Rentzepis P. M. Picosecond kinetics of events leading to reaction center bacteriochlorophyll oxidation. Science. 1975 Jun 27;188(4195):1301–1304. doi: 10.1126/science.188.4195.1301. [DOI] [PubMed] [Google Scholar]
  5. Kirmaier C., Holten D., Debus R. J., Feher G., Okamura M. Y. Primary photochemistry of iron-depleted and zinc-reconstituted reaction centers from Rhodopseudomonas sphaeroides. Proc Natl Acad Sci U S A. 1986 Sep;83(17):6407–6411. doi: 10.1073/pnas.83.17.6407. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. 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]
  7. Norris J. R., Bowman M. K., Budil D. E., Tang J., Wraight C. A., Closs G. L. Magnetic characterization of the primary state of bacterial photosynthesis. Proc Natl Acad Sci U S A. 1982 Sep;79(18):5532–5536. doi: 10.1073/pnas.79.18.5532. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Okamura M. Y., Isaacson R. A., Feher G. Primary acceptor in bacterial photosynthesis: obligatory role of ubiquinone in photoactive reaction centers of Rhodopseudomonas spheroides. Proc Natl Acad Sci U S A. 1975 Sep;72(9):3491–3495. doi: 10.1073/pnas.72.9.3491. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Rockley M. G., Windsor M. W., Cogdell R. J., Parson W. W. Picosecond detection of an intermediate in the photochemical reaction of bacterial photosynthesis. Proc Natl Acad Sci U S A. 1975 Jun;72(6):2251–2255. doi: 10.1073/pnas.72.6.2251. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Shuvalov V. A., Parson W. W. Energies and kinetics of radical pairs involving bacteriochlorophyll and bacteriopheophytin in bacterial reaction centers. Proc Natl Acad Sci U S A. 1981 Feb;78(2):957–961. doi: 10.1073/pnas.78.2.957. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Werner H. J., Schulten K., Weller A. Electron transfer and spin exchange contributing to the magnetic field dependence of the primary photochemical reaction of bacterial photosynthesis. Biochim Biophys Acta. 1978 May 10;502(2):255–268. doi: 10.1016/0005-2728(78)90047-6. [DOI] [PubMed] [Google Scholar]

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