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. 1984 Feb;81(4):1098–1101. doi: 10.1073/pnas.81.4.1098

Electron nuclear double resonance evidence supporting a monomeric nature for P700+ in spinach chloroplasts

Pádraig J O'Malley 1, Gerald T Babcock 1
PMCID: PMC344772  PMID: 16593417

Abstract

Proton electron nuclear double resonance (ENDOR) spectra of P700+ in spinach chloroplasts and in photosystem I particles have been obtained and compared with the corresponding ENDOR spectrum of monomeric chlorophyl a+ (Chla+) cation radical. The hyperfine couplings for P700+ can be interpreted in terms of those expected for a monomer Chla+ radical. The reduction in α-carbon spin densities observed for the in vivo species when compared to the in vitro radical is attributed to differences in the composition of the ground-state orbital for the two systems. For P700+, a mixture of 75% D0/25% D1, in which D0 and D1 represent the ground-and first excited-state orbitals calculated by Petke et al. for Chla+ [Petke, J. D., Maggiora, G. M., Shipman, L. L. & Christoffersen, R. E. (1980) Photochem. Photobiol. 31, 243-257], gives good agreement between calculated and experimental spin-density reduction factors. Interaction of the pigment ion with its protein environment such as through ligation of the central Mg atom, hydrogen bonding to the 9-keto-carbonyl group, and electrostatic interactions with charged amino acid residues are proposed as factors responsible for the lowering in energy of the D1 level in vivo. Combined with similar previous proposals for P680+ of photosystem II, the data suggest that both primary donor cation radicals of green plant photosynthesis can be viewed as monomeric Chla+ species in which the D1 orbital makes a significant contribution to the spin-density distribution.

Keywords: EPR, photosynthesis, hybrid orbital, reaction center

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Selected References

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

  1. Borg D. C., Fajer J., Felton R. H., Dolphin D. The pi-Cation Radical of Chlorophyll a. Proc Natl Acad Sci U S A. 1970 Oct;67(2):813–820. doi: 10.1073/pnas.67.2.813. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Clarke R. H., Hobart D. R. Structural aspects of the reaction center of photosynthetic bacteria calculated from triplet state zero-field splittings. FEBS Lett. 1977 Oct 1;82(1):155–158. doi: 10.1016/0014-5793(77)80908-3. [DOI] [PubMed] [Google Scholar]
  3. Davis M. S., Forman A., Fajer J. Ligated chlorophyll cation radicals: Their function in photosystem II of plant photosynthesis. Proc Natl Acad Sci U S A. 1979 Sep;76(9):4170–4174. doi: 10.1073/pnas.76.9.4170. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Eccles J., Honig B. Charged amino acids as spectroscopic determinants for chlorophyll in vivo. Proc Natl Acad Sci U S A. 1983 Aug;80(16):4959–4962. doi: 10.1073/pnas.80.16.4959. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Lutz M. Antenna chlorophyll in photosynthetic membranes. A study by resonance Raman spectroscopy. Biochim Biophys Acta. 1977 Jun 9;460(3):408–430. doi: 10.1016/0005-2728(77)90081-0. [DOI] [PubMed] [Google Scholar]
  6. Norris J. R., Scheer H., Druyan M. E., Katz J. J. An electron-nuclear double resonance (ENDOR) study of the special pair model for photo-reactive chlorophyll in photosynthesis. Proc Natl Acad Sci U S A. 1974 Dec;71(12):4897–4900. doi: 10.1073/pnas.71.12.4897. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Norris J. R., Scheer H., Katz J. J. Models for antenna and reaction center chlorophylls. Ann N Y Acad Sci. 1975 Apr 15;244:260–280. doi: 10.1111/j.1749-6632.1975.tb41535.x. [DOI] [PubMed] [Google Scholar]
  8. Norris J. R., Uphaus R. A., Katz J. J. Electron spin resonance in 13 C-labelled chlorophyll and 13 C-labelled algae. Biochim Biophys Acta. 1972 Aug 17;275(2):161–168. doi: 10.1016/0005-2728(72)90036-9. [DOI] [PubMed] [Google Scholar]
  9. Parson W. W., Cogdell R. J. The primary photochemical reaction to bacterial photosynthesis. Biochim Biophys Acta. 1975 Mar 31;416(1):105–149. doi: 10.1016/0304-4173(75)90014-2. [DOI] [PubMed] [Google Scholar]
  10. Robinson H. H., Sharp R. R., Yocum C. F. Effect of manganese on the nuclear magnetic relaxivity of water protons in chloroplast suspensions. Biochem Biophys Res Commun. 1980 Apr 14;93(3):755–761. doi: 10.1016/0006-291x(80)91141-9. [DOI] [PubMed] [Google Scholar]
  11. Rutherford A. W., Mullet J. E. Reaction center triplet states in photosystem I and photosystem II. Biochim Biophys Acta. 1981 Apr 13;635(2):225–235. doi: 10.1016/0005-2728(81)90022-0. [DOI] [PubMed] [Google Scholar]
  12. Wasielewski M. R., Norris J. R., Shipman L. L., Lin C. P., Svec W. A. Monomeric chlorophyll a enol: Evidence for its possible role as the primary electron donor in photosystem I of plant photosynthesis. Proc Natl Acad Sci U S A. 1981 May;78(5):2957–2961. doi: 10.1073/pnas.78.5.2957. [DOI] [PMC free article] [PubMed] [Google Scholar]

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