Structure and function of photosystem I

Current Opinion in Structural Biology

Volumn 6, Issue 4, 1996, Pages 473-484

  Fromme, Petra ^a  

^a TECHNISCHE UNIVERSITÄT BERLIN   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

CYTOCHROME C; FERREDOXIN; PLASTOCYANIN;

ANTENNA; ELECTRON TRANSPORT; ENERGY TRANSFER; PHOTOSYSTEM I; PRIORITY JOURNAL; REVIEW;

EID: 0029792161     PISSN: 0959440X     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0959-440X(96)80112-6     Document Type: Article

References (73)

1. Chitnis PR, Xu Q, Chirnis VP, Nechustai R. Function and organization of photosystem I polypeptides. Photosynth Res. 44:1995;23-40.
2. Golbeck JH. Photosystem I in cyanobacteria. Bryant D. Advances in Photosynthesis. Molecular Biology of Cyanobacteria). 1995;311-360 Kluver Academic Publishers, Dortrecht.
3. Pakrasi HB. Genetic analysis of the form and function of photosystem I and photosystem II. Annu Rev Genet. 29:1995;755-756.
4. of special interest Tjus SE, Robol-Boza M, Palson LO, Andersson B. Rapid isolation of hotosystem I chlorophyll-binding proteins by anion perfusion chromatography P. Photosynth Res. 45:1995;41-49 A new extremely rapid method of anion-exchange perfusion chromatography is used to subfractionate spinach PS I into its core complex and various components of the PS I light-harvesting antenna (LHC I).
5. of special interest Tsiotis G, Haase W, Engel A, Michel H. Isolation and structural characterization of trimeric cyanobacterial photosystem I complex with the help of recombinant antibody fragments. Eur J Biochem. 231:1995;823-830 A monoclonal antibody derived from mice reacts with a conformational epitope of the trimeric PS I complex from the cyanobacterium Synechocystis PCC 7002. With this antibody, a one-step purification of trimeric PS I is applied and the position of the bound Fv fragment is detected by EM and digital-image processing.
6. of outstanding interest Kruip J, Bald D, Hankamer B, Nield J, Boonstra AF, Barber J, Boekema EJ, Roegner M. Localization of subunits in PS 1, PS 2 and in a PS2/light harvesting supercomplex. Mathis P. Photosynthesis: from Light to Biosphere. 1995;405-408 Kluver Academic Publishers, Amsterdam, Photosynthetic complexes PS I and PS II from wild-type and mutant strains from cyanobacteria are analysed by EM. Structural information up to 15 Å resolution can be achieved, using single-particle analysis in combination with computer-supported image analysis. Localization of individual subunits (≥10 kDa) is achieved.
7. Kruip J, Boekema EJ, Bald D, Boonstra AF, Roegner M. Isolation and structural characterization of monomeric and trimeric photosystem I complexes (P700-FA/FB and P700-FX) from the cyanobacterium Synechocystis sp. PCC 6803. J Biol Chem. 68:1993;23353-23360.
8. B, and the coordination of P700 by helices of PsaA and PsaB are shown.
9. of special interest Xu Q, Chitnis PR. Organization of photosystem I polypeptides, identification of PsaB domains that may interact with PsaD. Plant Physiol. 108:1995;1067-1075 Incubation of the wild-type PS I with thermolysin yields 22kDa C-terminal fragments of PsaB that are resistant to further proteolysis, whereas a mutant lacking the PsaD subunit, this fragment is rapidly cleaved. In contrast, the absence of PsaE, PsaF, PsaI, PsaJ or PsaJ does not alter resistance to further proteolysis. It is proposed that PsaD shields two extramembrane loops of PsaB and protects the C-terminal domain from PsaB from proteolysis in vitro.
10. +, flash-induced absorbance difference spectrum and shift of redox potential, indicating that the direct environment of P700 is modified by this mutation.
11. B centres are altered in the C576L mutant.
12. x in electron transport.
13. X.
14. of special interest Rodday SM, Webber AN, Bingham SE, Biggins J. Evidence that the Fx domain in photosystem I interacts with the subunits PsaC: side directed changes in PsaB destabilize the subunit interaction in Chlamydomonas rheinhardtii. Biochemistry. 34:1995;6328-6334 Site-directed mutagenesis in the interhelical loop between helices 8 and 9 in Chlamydomonas shows the prominent role of one or both of the arginine residues in the putative core binding site and in its interaction with the negative charged domains in the PsaC subunit.
15. x are changed for D566 mutants only. Therefore, a prominent role for these negatively charged amino acids is unlikely. In contrast, mutation of K547E indicates the possible involvement of this positively charged amino acid in the interaction of PsaB and PsaC.
16. of special interest Xu Q, Hoppe D, Chitnis VP, Odom WR, Guikema JA, Chitnis PR. Mutational analysis of photosystem I polypeptides in the cyanobacterium Synechocystis sp. PCC 6803: target inactivation of psaI reveals the function of PsaI in the structural organization of PsaL. J Biol Chem. 270:1995;16243-16250 A deletion strain of PsaI is generated, showing a strong structural interaction of the subunits PsaI and PsaL that stabilizes the association of PsaL with the PS I core. Inactivation of PsaI leads to an 80% decrease in the PsaL level in the photosynthetic membranes and a complete loss of PsaL in the purified PS I preparations. No trimers can be isolated from the membrane. Furthermore, PsaL is increased susceptible to proteolysis. The mutants cells grow slower and contain less chlorophylls than wild-type cells when grown at 40°C (possible role for trimers: thermostability of PS I?).
17. Andersen B, Scheller HV. Structure, function and assembly of photosystem I. Sundquist C. Pigment Protein Complexes in Plastids: Synthesis and Assembly. 1993;383-418 Academic Press, San Diego. Cell Biology: A Series of Monographs.
18. Falzone CJ, Kao Y-H, Zao J, Bryant DA, Lecomte TTJ. The three dimensional solution structure of PsaE from the cyanobacterium Synechococcus sp. strain PCC 7002: a photosystem I protein that shows structural homology with SH3 domain. Biochemistry. 33:1994;6052-6062.
19. of special interest Lagoutte B, Barth P, Setif P. Photosystem I/ferredoxin interaction: site directed mutagenesis of PSI-E. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;71-74 Kluver Academic Publishers, Amsterdam, Site-directed mutations are introduced in PsaE from Synechocysis PCC 6803. The N-terminal sequence and the C-terminal eight amino acids are shown to be necessary for the precise anchorage of PsaC into PS I. Furthermore, the mutation of Arg9 into glutamine has a dramatic effect on the reduction of ferredoxin.
20. Adman ET, Sieker LC, Jensen LH. The structure of a bacterial ferredoxin. J Biol Chem. 248:1973;3987-3996.
21. -) in PS I single crystals provide evidence for a structural analogy of the cores of ferredoxin from P. aerogenis and PsaC, and allow the orientation of PsaC in PS I to be determined, such that only a two-fold ambiguity in the PsaC orientation remains. The results imply an assignment of g-tensor axes to the [4Fe4S] cube structure.
22. x cores.
23. A′ site.
24. B′.
25. x cores.
26. B (cf [27]).
27. x core. The loop-deleted PsaC is unable to bind to PsaA/PsaB in the absence of PsaD, whereas in the C-terminal-deleted PsaC, PsaA/B binding is normal but interaction with PsaD is reduced.
28. A′ is detected in the C50D mutant.
29. of special interest Setif P, Hanley J, Barth P, Bottin H, Lagoutte B. Ferredoxin reduction by PS 1 with wild type, deleted and site-directed mutants from the cyanobacterium Synechocystis sp. PCC 6803. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;23-28 Kluver Academic Publishers, Amsterdam, Reduction of ferredoxin is investigated in the absence of either PsaD or PsaE and in site-directed mutants of these subunits. For both deletion mutants, ferredoxin affinity for PS I is decreased at least 16-fold compared with the wild-type. From the results of site-directed mutagenesis, it is suggested that both subunits are involved in ferredoxin docking: PsaE is more essential for tight binding of ferredoxin through one of his basic amino acids, R9, whereas comparison of the second-order rate constants show that ferredoxin reduction is altered more in the absence of PsaD.
30. of outstanding interest Mühlenhoff U, Kruip J, Bryant DA, Rögner M, Setif P, Boekema E. Characterization of a redox-active cross-linked complex between cyanobacterial photosystem I and its physiological acceptor flavodoxin. EMBO J. 15:1996;488-497 A covalent complex between PS I and flavodoxin from the cyanobacterium Synechococcus sp. PCC 7002 is generated by chemical cross-linking. Flavodoxin can be photoreduced in these complexes; the kinetics display three exponential components, with half-life times of 9s, 70s and 1 ms. The docking site of flavodoxin is determined by EM in combination with image analysis. Flavodoxin binds at the cytoplasmatic (stromal) side of PS I at a distance of 7 Å from the centre of the trimer and in close cantact to a ridge formed by the subunits PsaC, PsaD and PsaE.
31. of outstanding interest Lelong C, Boekema E, Kruip J, Bottin H, Rögner M, Setif P. Characterization of a redox active cross-linked complex between cyanobacterial photosystem I and soluble ferredoxin. EMBO J. 15:1996;101-109 The docking site of ferredoxin on PS I is determined by EM in combination with image analysis on a covalent stoichiometric cross-linked complex between PS I and ferredoxin. The latter binds to the cytoplasmatic side of PS I, with its mass centre 77 Å distant from the center of the trimer and in close contact with a ridge formed by the subunits PsaC, PsaD and PsaE. This docking site corresponds to a close proximity between the [2Fe2S] cluster of ferredoxin and the terminal [4Fe4S] cluster of PS I, and is very similar in position to the docking site of flavodoxin.
32. of special interest Mühlenhoff U, Setif P. Laser flash absorption spectroscopy study of flavodoxin reduction by photosystem I in Synechococcus sp. PCC 7002.6. Biochemistry. 35:1996;1367-1374 The photoreduction of flavodoxin by trimeric PS I from Synechococcus sp. PCC 7002 is investigated by flash-absorption spectroscopy. Conditions are established under which the reductions of the oxidized and semiquinone forms of flavodoxin can be studied sparately. Both processes are identified by their differential spectra measured over the range 460-630nm. The kinetics of reduction of oxidized flavodoxin display a single-exponential component, whereas the reduction of flavodoxin semiquinone is biphasic, indicating slightly different interactions between PS I and flavodoxin in its oxidized and semiquinone states.
33. -, the terminal 4Fe-4S acceptors of PS I, to ferredoxin. A detailed examination indicates that the intermediate (13-20μs) and slow (103-123μs) first-order phases are associated with two distinct ferredoxin-binding sites on PS I. The kinetics of ferredoxin reduction are much faster at pH 5.8 in the absence of salt than are the kinetics at pH 8 in the presence of salts, indicating a higher affinity for ferredoxin at lower pH.
34. Fromme P, Schubert W-D, Krauß N. Structure of photosystem I: suggestions on docking sites for plastocyanin and ferredoxin, and the coordination of P700. Biochim Biophys Acta. 1187:1994;99-105.
35. + reductase, and cytochrome c. Arch Biochem Biophys. 321:1995;229-238 Non-conservative mutations in ferredoxin at F65 and E94, which have been shown to result in very large inhibitions of electron transfer to FNR, are found to yield wild-type behavior in reactions with PS I. It is concluded that the structural requirements for efficient electron transfer involving the ferredoxin and flavodoxin molecules differ, depending upon the reactant with which these redox proteins interact. This implies that different conserved residues in these proteins have evolved to satisfy the varying requirements of particular reaction partners.
36. 6 may use just one electron-transfer site close to the heme unit, in its reactions with both redox partners PS I and cytochrome f; in contrast, plastocyanine uses two different sites in plastocyanine in mediating in electron transfer to PS I and cytochrome f.
37. Xu Q, Yu L, Chitnis VP, Chitnis PR. Function and organization of photosystem I in cyanobacterial mutant strain, that lacks PsaF and PsaJ subunits. J Biol Chem. 269:1994;3205-3211.
38. +, the oxidized RC chlorophyll dimer, is dramatically reduced in the mutant, indicating that the PsaF subunit plays an important role in docking plastocyanin to the PS I complex.
39. of outstanding interest Drepper F, Hippler M, Nitschke W, Haehnel W. Binding dynamics and electron transfer between plastocyanin and photosystem I. Biochemistry. 35:1996;1282-1295 The mechanism of the electron transfer from plastocyanin to PS I from spinach is studied. The dissociation constant of oxidized plastocyanin is about six times larger than that for reduced plastocyanin, and the midpoint redox potential of PS I-bound plastocyanin is 50-60mV higher than that of soluble plastocyanin. Double-flash excitation shows that oxidized plastocyanin must leave the complex after the electron transfer before a new reduced plastocyanin molecule can bind to PS I, limiting the turnover of PS I to a half-life of ∼60s. All data are consistently described by a model including the formation of a complex at a single binding site of PS I, stabilized by electrostatic and hydrophobic interactions.
40. 6 by plastocyanin, as well as the appearance of the fast kinetic phase in the plastocyanin/PS I system of higher plants, involves structural modifications in both the donor protein and PS I.
41. 6 has been carried out by laser-flash absorption spectroscopy in the cyanobacteria Anabaena and Synechocystis, as well as in spinach. Long-range electrostatic interactions appear to be attractive in Anabaena, but repulsive in Synechocystis and spinach, indicating that the electron-transfer step seems to be well optimized in the Anabaena cyt - PS I couple, which exhibits a temperature-independent fast kinetic phase and, therefore, a low activation energy barrier. Short-distance forces appear to have gained relevance in the reaction mechanism of PS I reduction by cyt and plastocyanin throughout evolution, whereas long-range interactions are prevalent in less evolved organisms.
42. Haehnel W, Jansen T, Gause K, Kloesgen RB, Stahl B, Michl D, Huvermann B, Karas M, Herrmann RG. Electron transfer from plastocyanin to photosystem I. EMBO J. 13:1994;1028-1038.
43. of special interest Lee BH, Hibino T, Takabe T, Weisbeek PJ, Takabe T. Site-directed mutant study on the role of negative patches on Silene plastocyanin in the interactions with cytochrome f and photosystem I. J Biochem. 117:1995;1209-1217 Six mutants from Silene pratensis are constructed by site-directed mutagenesis, to investigate the role of two highly conserved negative patches, residues 42-45 and 59-61, on the surface of plant plastocyanin. The electron-transfer rate from cyt f to plastocyanin is shown to decrease exponentially as the net charge on the negative patch (42-45) increases, whereas the modification of the second negative patch (59-61) had no effect. In the case of electron transfer to PS I, essentially similar results are observed, although a slight participation of the negative patch (59-61) is suggested. On the basis of these results, the electron-transfer pathway from the heme to P700 via plastocyanin is discussed in relation to the role of charged amino acid residues.
44. of outstanding interest Sigfridsson K, Young S, Hansson O. Structural dynamics in the plastocyanin - photosystem I electron-transfer complex as revealed by mutant studies. Biochemistry. 35:1996;1249-1257 A series of plastocyanin mutants is constructed by site-directed mutagenesis, and is expressed in E. coli to elucidate the interaction between plastocyanin and PS I in the photosynthetic ETC (Leu12→Ala,Asp,Glu,Lys; Tyr-83→His,Phe,Leu; Phe-35, Asp-42, and Gln-88→Tyr, Asp, Glu). Only the Leu-12 mutants show any major change in their PS I whereas, while the mutants in the acidic patch show minor changes, suggesting that both the hydrophobic and acidic patches make contact with PS I but that the electron transfer occurs at the hydrophobic interface, most probably via the His-87 residue.
45. +: (a) the special pair model with a strongly asymmetric spin density distribution over the dimer halves; and (b) the model of a strongly perturbed chl a monomer.
46. +. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;183-188 Kluver Academic Publishers, Amsterdam.
47. +: spectral simulations and their implications for electronic structures. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;35-38 Kluver Academic Publishers, Amsterdam.
48. Hamacher E, Kruip J, Rögner M, Mäntele W. Characterization of the primary electron donor of photosystem I, P700, by electrochemistry and Fourier transform infrared (FTIR) difference spectroscopy. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;95-98 Kluver Academic Publishers, Amsterdam.
49. Käß H. Dissertation. 1995;Technisches Universität, Berlin.
50. +) is observed in the absorption spectra of the reduced and oxidized particles, respectively. Stable charge separation is restored upon the addition of 2-amino-athraquinone.
51. Iwaki M, Kumazaki S, Yoshihara K, Erabi T, Itoh S. G dependence of the rate constant of P700+ AO- P700+Q-reaction in the quinone-reconstituted PS I reaction center. Mathis P. Photosynthesis: from light to Biosphere. 2:1995;147-150 Kluver Academic Publishers, Amsterdam.
52. - formation. Biochemistry. 33:1994;8619-8624.
53. 0 reduction appears to contain contributions from more than a single chl pigment.
54. of special interest. Femtosecond transient absorption spectroscopy is used to investigate the energy-transfer and trapping processes in both intact membranes and purified detergent-isolated particles from a mutant of Synechocystis that lacks PS II. The spectra and lifetimes are very similar, suggesting little disruption of the core antenna as a result of detergent treatment. For the detergent-isolated particles, three different excitation wavelengths are used to excite different distributions of pigments in the spectrally heterogeneous core antenna. Lifetimes of 2.7-4.3ps are attributed to evolution from the initially excited distribution of pigments to the equilibrated excited state distribution, showing strongly excitation wavelength dependency. Lifetimes of 24-28ps are associated with trapping. The trapping process gives rise to a non-decaying spectrum that is attributable to oxidation of the primary electron donor._rffrt of special interest Hastings G, Reed LJ, Lin S, Blankenship RE. Excited state dynamics in photosystem I: effects of detergent and excitation wavelength. Biophys J. 69:1995;2044-2055 Femtosecond transient absorption spectroscopy is used to investigate the energy-transfer and trapping processes in both intact membranes and purified detergent-isolated particles from a mutant of Synechocystis that lacks PS II. The spectra and lifetimes are very similar, suggesting little disruption of the core antenna as a result of detergent treatment. For the detergent-isolated particles, three different excitation wavelengths are used to excite different distributions of pigments in the spectrally heterogeneous core antenna. Lifetimes of 2.7-4.3ps are attributed to evolution from the initially excited distribution of pigments to the equilibrated excited state distribution, showing strongly excitation wavelength dependency. Lifetimes of 24-28ps are associated with trapping. The trapping process gives rise to a non-decaying spectrum that is attributable to oxidation of the primary electron donor. The lifetimes and spectra associated with trapping and radical pair formation are independent of excitation wavelength, suggesting that trapping proceeds from an equilibrated excited state. It is suggested that the pigments in the PS I core antenna display some degree of excitonic coupling.
55. A in the zinc-based RCs. It is suggested that the differences in the orientation and the g values of the quinones in the two RCs arise from weaker binding to the protein in PS I.
56. Barkoff A, Brunkan N, Snyder SW, Ostafin A, Werst M, Biggins J, Thunauer MCL. Quinone exchange at the AI site in photosystem I (PS I). Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;115-118 Kluver Academic Publishers, Amsterdam.
57. 1) in the photosystem I reaction centre. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;163-166 Kluver Academic Publishers, Amsterdam, The electronic structure of the semiquinone anion radical in PS I is studied by ENDOR and TRIPLE(ST) resonance spectroscopies in conjunction with biosynthetic deuteration in vivo. The results reveal protein - quinone hydrogen bonding in PS I and a perturbation of the electronic structure of the bound phylloquinone.
58. Schlodder E, Brettel K, Falkenberg K, Gergeleit M. Temperature dependence of the reoxidation kinetics of AI - in PS 1. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;107-110 Kluver Academic Publishers, Amsterdam.
59. A are removed, and only slightly temperature dependent over the range of 298-10K.
60. Frank H, Cogdell RJ. Carotinoids in photosynthesis. Photochem Photobiol. 63:1996;257-264.
61. 2, 50% of its chl is lost by photo-oxidation within 4 or 1.5h, respectively.
62. 735). The relative quantum yield of F760 quenching is not dependent on the wavelength of excitation in the region 62.
63. of special interest Palsson L-O, Tjus SE, Andersson B, Gillbro T. Energy transfer in photosystem I. Time resolved fluorescence of the native photosystem I complex and its core complex. Chem Phys. 194:1995;291-302 Energy transfer within isolated spinach PS I complexes with different antenna size is studied using time-resolved picosecond and steady-state fluorescence spectroscopy. In both the native PS I complexes and the PS I core complexes lacking the outer chl a/b antenna, a fast dominating emission component of ∼35ps is observed at room temperature; this component is associated with the trapping process by the RC. In the native PS I complex, a 120ps component that is not observed in the PS I core complex is observed, most likely representing an energy transfer from low-energy pigments in the LHC I antenna and into the core. Because of the very fast energy equilibration (<10ps), it is not possible to resolve the energy transfer at room temp. At 77K, it is possible to follow the energy transfer from F690 to F720 with a transfer time of ∼35ps within the native PS I complex, and 78ps in the PS I core complex.
64. Sopko B, Sofrova D, Hladik J, Gulyayev BA, Tetenkin VL. The role of long wavelength absorbing chlorophylls in trimetic PS I isolated from cyanobacterium Synechococcus elongatus. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;47-50 Kluver Academic Publishers, Amsterdam.
65. Trinkunas G, Holzwarth AR. On the spatial distribution of chlorophyll spectral types in photosystem I. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;51-54 Kluver Academic Publishers, Amsterdam.
66. Pälsson LO, Schlodder E, van Grondelle R, Dekker JP. Properties of the long-wavelength emitting chlorophylls in isolated photosystem I particles of Synechococcus sp. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;195-198 Kluver Academic Publishers, Amsterdam.
67. of outstanding interest DiMagno L, Chan C-K, Jia Y, Lang MJ, Newman JR, Mets L, Fleming GR, Haselkorn R. Energy transfer and trapping in photosystem I reaction centers from cyanobacteria. Proc Natl Acad Sci USA. 92:1995;2715-2719 A mutant strain of Synechocystis 6803 is constructed, leaving PS I as the sole chromophore in photosynthetic membranes. A decay component of 25ps dominates (99% of amplitude) the fluorescence of the membrane sample, implying that excitations in the PS I core antenna are efficiently trapped at the RCs. The experimental results are compared with several computer simulations, and kinetics are modelled for an antenna size comprising 130 chls (leading to a charge separation time of -1ps) and a two-domain antenna model, each containing 65 chls (leading to a 3-4ps charge separation time).
68. of outstanding interest Valkunas L, Liuolia V, Dekker JP, van Grondelle R. Description of energy migration and trapping in photosystem I by a model with two distance scaling parameters. Photosyn Res. 43:1995;149-154 The energy-transfer and trapping kinetics in the core antenna of PS I are described in a new model, in which the distance between the core antenna chls and P700 is proposed to be considerably longer than the distance between the chls within the antenna. Structurally, the model describes the PS I core antenna as a regular sphere around P700, while energetically it consists of three levels representing the bulk antenna, P700 and the red-shifted antenna pigments absorbing at longer wavelength than P700, in good agreement with experimental data. The excitation energy transfer and trapping in PS I are described as a `transfer-to-the-trap'-limited process.
69. of outstanding interest Hauska G, Hager-Braun C, Schneebauer N, Schütz M, Zimmermann R, Nelson N. Biochemical aspects of the reaction center in green sulfur bacteria-comparison with other FeS-types. Mathis P. Photosynthesis: from Light to Biosphere. 2:1995;11-16 Kluver Academic Publishers, Amsterdam, Recent results comparing the structure and function of the two types of RC in green sulfur bacteria are reviewed. It is assumed that the homodimeric RCs preceded the heterodimers and that the ancestor was of the FeS type.
70. Vermass WFJ. Evolution of heliobacteria: implications for photosynthetic reaction center complexes. Photosynth Res. 41:1994;285-294.
71. Fromme P, Witt HT, Schubert WD, Klukas O, Saenger W, Krauß N. Structure of photosystem I at 4.5 Å resolution - a short review including evolutionary aspects. Biochim Biophys Acta. 1996;. in press.
72. of outstanding interest Jansson S, Andersen B, Scheller VH. Cross-linking studies of PS I: nearest neighbour analysis of higher plant photosystem I holocomplex. Plant Physiol. 1996; Different photosystem I preparations from barley and spinach are subjected to chemical cross-linking using DTSP and DTSSP. A large number of crosslinking products are identified by two dimensional gel electrophoresis and immunoblotting. It is deduced that the subunits PsaD, PsaH, PsaI and PsaL occupy one side of the complex, whereas PseE, PsaF and PsaJ occupy the other. Lhca2 and Lhca3 form homodimers, whereas Lhca1 and Lhca4 could be heterdimers.
73. 0 and the accessory chls in both exciton and energy transfer.