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. 1995 Aug;69(2):652–659. doi: 10.1016/S0006-3495(95)79941-6

Chemical platinization and its effect on excitation transfer dynamics and P700 photooxidation kinetics in isolated photosystem I.

J W Lee 1, I Lee 1, P D Laible 1, T G Owens 1, E Greenbaum 1
PMCID: PMC1236290  PMID: 8527679

Abstract

Isolated photosystem I (PSI) reaction center/core antenna complexes (PSI-40) were platinized by reduction of [PtCl6]2- at 20 degrees C and neutral pH. PSI particles were visualized directly on a gold surface by scanning tunneling microscopy (STM) before and after platinization. STM results showed that PSI particles were monomeric and roughly ellipsoidal with major and minor axes of 6 and 5 nm, respectively. Platinization deposited approximately 1000 platinum atoms on each PSI particle and made the average size significantly larger (9 x 7 nm). In addition to direct STM visualization, the presence of metallic platinum on the PSI complexes was detected by its effect of actinic shading and electrostatic shielding on P700 photooxidation and P700+ reduction. The reaction centers (P700) in both platinized and nonplatinized PSI-40 were photooxidized by light and reduced by ascorbate repeatedly, although at somewhat slower rates in platinized PSI because of the presence of platinum. The effect of platinization on excitation transfer and trapping dynamics was examined by measuring picosecond fluorescence decay kinetics in PSI-40. The fluorescence decay kinetics in both platinized and control samples can be described as a sum of three exponential components. The dominant (amplitude 0.98) and photochemically limited excitation lifetime remained the same (16 ps) before and after platinization. The excitation transfer and trapping in platinized PSI-40 was essentially as efficient as that in the control (without platinization) PSI. The platinization also did not affect the intermediate-lifetime (400-600 ps) and long-lifetime (> 2500 ps) components, which likely are related to intrinsic electron transport and to functionally uncoupled chlorophylls, respectively. The amplitudes of these two components were exceptionally small in both of the samples. These results provide direct evidence that although platinization dramatically alters the photocatalytic properties of PSI, it does not alter the intrinsic excitation dynamics and initial electron transfer reactions in PSI.

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Selected References

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

  1. Greenbaum E. Platinized chloroplasts: a novel photocatalytic material. Science. 1985 Dec 20;230(4732):1373–1375. doi: 10.1126/science.230.4732.1373. [DOI] [PubMed] [Google Scholar]
  2. Hitchens G. D., Rogers T. D., Murphy O. J., Patterson C. O. A new photocatalytic material based on algal cells. Biochem Biophys Res Commun. 1991 Mar 29;175(3):1029–1035. doi: 10.1016/0006-291x(91)91668-3. [DOI] [PubMed] [Google Scholar]
  3. Hiyama T., Ke B. Difference spectra and extinction coefficients of P 700 . Biochim Biophys Acta. 1972 Apr 20;267(1):160–171. doi: 10.1016/0005-2728(72)90147-8. [DOI] [PubMed] [Google Scholar]
  4. Jean J. M., Chan C. K., Fleming G. R., Owens T. G. Excitation transport and trapping on spectrally disordered lattices. Biophys J. 1989 Dec;56(6):1203–1215. doi: 10.1016/S0006-3495(89)82767-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Jia Y., Jean J. M., Werst M. M., Chan C. K., Fleming G. R. Simulations of the temperature dependence of energy transfer in the PSI core antenna. Biophys J. 1992 Jul;63(1):259–273. doi: 10.1016/S0006-3495(92)81589-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Ke B. One-way electron discharge subsequent to the photochemical charge separation in photosystem I. Biochim Biophys Acta. 1972 Jun 23;267(3):595–599. doi: 10.1016/0005-2728(72)90192-2. [DOI] [PubMed] [Google Scholar]
  7. Laible P. D., Zipfel W., Owens T. G. Excited state dynamics in chlorophyll-based antennae: the role of transfer equilibrium. Biophys J. 1994 Mar;66(3 Pt 1):844–860. doi: 10.1016/s0006-3495(94)80861-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Mann S., Archibald D. D., Didymus J. M., Douglas T., Heywood B. R., Meldrum F. C., Reeves N. J. Crystallization at Inorganic-organic Interfaces: Biominerals and Biomimetic Synthesis. Science. 1993 Sep 3;261(5126):1286–1292. doi: 10.1126/science.261.5126.1286. [DOI] [PubMed] [Google Scholar]
  9. Markwell J. P., Thornber J. P., Skrdla M. P. Effect of detergents on the reliability of a chemical assay for P-700. Biochim Biophys Acta. 1980 Jul 8;591(2):391–399. doi: 10.1016/0005-2728(80)90170-x. [DOI] [PubMed] [Google Scholar]
  10. Melis A. Kinetic analysis of P-700 photoconversion: effect of secondary electron donation and plastocyanin inhibition. Arch Biochem Biophys. 1982 Sep;217(2):536–545. doi: 10.1016/0003-9861(82)90535-5. [DOI] [PubMed] [Google Scholar]
  11. Owens T. G., Webb S. P., Alberte R. S., Mets L., Fleming G. R. Antenna structure and excitation dynamics in photosystem I. I. Studies of detergent-isolated photosystem I preparations using time-resolved fluorescence analysis. Biophys J. 1988 May;53(5):733–745. doi: 10.1016/S0006-3495(88)83154-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Owens T. G., Webb S. P., Mets L., Alberte R. S., Fleming G. R. Antenna size dependence of fluorescence decay in the core antenna of photosystem I: estimates of charge separation and energy transfer rates. Proc Natl Acad Sci U S A. 1987 Mar;84(6):1532–1536. doi: 10.1073/pnas.84.6.1532. [DOI] [PMC free article] [PubMed] [Google Scholar]

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