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. 1978 Feb 15;170(2):373–378. doi: 10.1042/bj1700373

Quantitative electron-paramagnetic-resonance measurements of the electron-transfer components of the photosystem-I reaction centre. The reaction-centre chlorophyll (P700), the primary electron acceptor X and bound iron-sulphur centre A.

P Heathcote, D L Williams-Smith, M C Evans
PMCID: PMC1183904  PMID: 205210

Abstract

An e.p.r. spectrum of the reduced form of the electron-transport component (X), thought to be the primary electron acceptor of Photosystem I, was obtained. By using line-shape simulations of this component and the free-radical e.p.r. signal I of the oxidized reaction-centre chlorophyll (P700), it was possible to determine the ratio of the number of electron spins to which these signals correspond in Photosystem-I particles under a variety of conditions. On illumination at cryogenic temperatures of Photosystem-I preparations, in which both bound iron-sulphur centres A and B were reduced, the measured ratio of free radical to component X varied between 1.04 and 2.23, with an average value of 1.54 +/- 0.18 where a Gaussian line-shape is assumed for the component-X signal in the simulation. The error in this measurement is estimated to be up to 50%. In a similar way component X and centre A of the bound iron-sulphur protein were quantified, the ratio between these two components varying between 1.26 and 0.61 with an average value of 0.75 +/- 0.06. These results indicate that the quantitative relationship, in terms of net electron spins, between centre A, component X and P700 is of the order to be expected if component X is indeed the primary electron acceptor in Photosystem I and a component of the photosynthetic electron-transport chain.

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Selected References

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

  1. BEINERT H., KOK B., HOCH G. The light induced electron paramagnetic resonance signal of photocatalyst P700. Biochem Biophys Res Commun. 1962 Apr 20;7:209–212. doi: 10.1016/0006-291x(62)90176-6. [DOI] [PubMed] [Google Scholar]
  2. Bearden A. J., Malkin R. Quantitative EPR studies of the primary reaction of photosystem I in chloroplasts. Biochim Biophys Acta. 1972 Dec 14;283(3):456–468. doi: 10.1016/0005-2728(72)90262-9. [DOI] [PubMed] [Google Scholar]
  3. Cammack R., Evans M. C. E.P.R. spectra of iron-sulphur proteins in dimethylsulphoxide solutions: evidence that chloroplast photosystem I particles contain 4Fe-4S centres. Biochem Biophys Res Commun. 1975 Nov 17;67(2):544–549. doi: 10.1016/0006-291x(75)90846-3. [DOI] [PubMed] [Google Scholar]
  4. Commoner B., Heise J. J., Townsend J. LIGHT-INDUCED PARAMAGNETISM IN CHLOROPLASTS. Proc Natl Acad Sci U S A. 1956 Oct;42(10):710–718. doi: 10.1073/pnas.42.10.710. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Evans E. H., Cammack R. Properties of the primary electron acceptor complex of photosystem I in the blue green alga Chlorogloea fritschii. Biochem Biophys Res Commun. 1976 Feb 23;68(4):1212–1218. doi: 10.1016/0006-291x(76)90326-0. [DOI] [PubMed] [Google Scholar]
  6. Evans M. C., Cammack R. The effect of the redox state of the bound iron-sulphur centres in spinach chloroplasts on the reversibility of P700 photooxidation at low temperatures. Biochem Biophys Res Commun. 1975 Mar 3;63(1):187–193. doi: 10.1016/s0006-291x(75)80028-3. [DOI] [PubMed] [Google Scholar]
  7. Evans M. C., Reeves S. G., Cammack R. Determination of the oxidation-reduction potential of the bound iron-sulphur proteins of the primary electron acceptor complex of photosystem I in spinach chloroplasts. FEBS Lett. 1974 Dec 1;49(1):111–114. doi: 10.1016/0014-5793(74)80644-7. [DOI] [PubMed] [Google Scholar]
  8. Evans M. C., Sihra C. K., Cammack R. The properties of the primary electron acceptor in the Photosystem I reaction centre of spinach chloroplasts and its interaction with P700 and the bound ferredoxin in various oxidation-reduction states. Biochem J. 1976 Jul 15;158(1):71–77. doi: 10.1042/bj1580071. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Evans M. C., Telfer A., Lord A. V. Evidence for the role of a bound ferredoxin as the primary electron acceptor of photosystem I in spinach chloroplasts. Biochim Biophys Acta. 1972 Jun 23;267(3):530–537. doi: 10.1016/0005-2728(72)90181-8. [DOI] [PubMed] [Google Scholar]
  10. Heathcote P., Williams-Smith D. L., Evans M. C. Quantitative electron-paramagnetic-resonance measurements of the electron-transfer components of the photosystem-I reaction centre. The reaction-centre chlorophyll (P700), the primary electron acceptor X and bound iron-sulphur centre A. Biochem J. 1978 Feb 15;170(2):373–378. doi: 10.1042/bj1700373. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. KOK B. On the reversible absorption change at 705 mu in photosynthetic organisms. Biochim Biophys Acta. 1956 Nov;22(2):399–401. doi: 10.1016/0006-3002(56)90172-x. [DOI] [PubMed] [Google Scholar]
  12. Kimura T., Tasaki A., Watari H. Studies on adrenal steroid hydroxylases. The magnetic susceptibility of oxidized and reduced adrenal iron-sulfur protein (adrenodoxin). J Biol Chem. 1970 Sep 10;245(17):4450–4452. [PubMed] [Google Scholar]
  13. Malkin R., Bearden A. J. Primary reactions of photosynthesis: photoreduction of a bound chloroplast ferredoxin at low temperature as detected by EPR spectroscopy. Proc Natl Acad Sci U S A. 1971 Jan;68(1):16–19. doi: 10.1073/pnas.68.1.16. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. McIntosh A. R., Chu M., Bolton J. R. Flash photolysis electron spin resonance studies of the electron acceptor species at low temperatures in photosystem I of spinach subchloroplast particles. Biochim Biophys Acta. 1975 Feb 17;376(2):308–314. doi: 10.1016/0005-2728(75)90023-7. [DOI] [PubMed] [Google Scholar]
  15. Mcintosh A. R., Bolton J. R. Electron spin resonance spectrum of species "X" which may function as the primary electron acceptor in photosystem I of green plant photosynthesis. Biochim Biophys Acta. 1976 Jun 8;430(3):555–559. [PubMed] [Google Scholar]
  16. Moss T. H., Petering D., Palmer G. The magnetic susceptibility of oxidized and reduced ferredoxins from spinach and parsley and the high potential protein from Chromatium. J Biol Chem. 1969 May 10;244(9):2275–2277. [PubMed] [Google Scholar]

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