O Hansson

Chalmers University of Technology, Göteborg, Vaestra Goetaland, Sweden

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Publications (24)88.59 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A set of plastocyanin (Pc) mutants, probing the small acidic patch (Glu59, Glu60, and Asp61) and a nearby residue, Gln88, has been constructed to provide further insight into the electron transfer process between Pc and photosystem 1. The negatively charged residues were changed into their neutral counterparts or to a positive lysine. All mutant proteins exhibited electron transfer kinetics qualitatively similar to those of the wild type protein over a wide range of Pc concentrations. The kinetics were slightly faster for the Gln88Lys mutant, while they were significantly slower for the Glu59Lys mutant. The data were analyzed with two different models: one involving a conformational change of the Pc-photosystem 1 complex that precedes the electron transfer step (assumed to be irreversible) [Bottin, H., and Mathis, P. (1985) Biochemistry 24, 6453-6460] and another where no conformational change occurs, the electron transfer step is reversible, and dissociation of products is explicitly taken into account [Drepper, F., Hippler, M., Nitschke, W., and Haehnel, W. (1996) Biochemistry 35, 1282-1295]. Both models can account for the observed kinetics in the limits of low and high Pc concentrations. To discriminate between the models, the effects of added magnesium ions on the kinetics were investigated. At a high Pc concentration (0.7 mM), the ionic strength dependence was found to be consistent with the model involving a conformational change but not with the model where the electron transfer is reversible. One residue in the small acidic patch, Glu60, seems to be responsible for the major part of the ionic strength dependence of the kinetics.
    Biochemistry 01/2000; 38(50):16695-705. · 3.38 Impact Factor
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    ABSTRACT: This is a comparative study of the photoinduced (so-called forward) electron-transfer reaction 3Zncyt/pc(II) --> Zncyt+/pc(I), between the triplet state of zinc cytochrome c (3Zncyt) and cupriplastocyanin [pc(II)], and the thermal (so-called back) electron-transfer reaction Zncyt+/pc(I) --> Zncyt/pc(II), between the cation (radical) of zinc cytochrome c (Zncyt+) and cuproplastocyanin [pc(I)], which follows it. Both reactions occur between associated (docked) reactants, and the respective unimolecular rate constants are kF and kB. Our previous studies showed that the forward reaction is gated by a rearrangement of the diprotein complex. Now we examine the back reaction and complare the two. We study the effects of temperature (in the range 273.3-302.9 K) and viscosity (in the range 1.00-17.4 cP) on the rate constants and determine enthalpies (DeltaH), entropies (DeltaS), and free energies (DeltaG) of activation. We compare wild-type spinach plastocyanin, the single mutants Tyr83Leu and Glu59Lys, and the double mutant Glu59Lys/Glu60Gln. The rate constant kB for wild-type spinach plastocyanin and its mutants markedly depends on viscosity, an indication that the back reaction is also gated. The activation parameters DeltaH and DeltaS show that the forward and back reactions have similar mechanisms, involving a rearrangement of the diprotein complex from the initial binding configuration to the reactive configuration. The rearrangements of the complexes 3Zncyt/pc(II) and Zncyt+/pc(I) that gate their respective reactions are similar but not identical. Since the back reaction of all plastocyanin variants is faster than the forward reaction, the difference in free energy between the docking and the reactive configuration is smaller for the back reaction than for the forward reaction. This difference is explained by the change in the electrostatic potential on the plastocyanin surface as Cu(II) is reduced to Cu(I). It is the smaller DeltaH that makes DeltaG smaller for the back reaction than for the forward reaction.
    Biochemistry 03/1999; 38(5):1589-97. · 3.38 Impact Factor
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    Y Xue, M Okvist, O Hansson, S Young
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    ABSTRACT: The crystal structure of plastocyanin from spinach has been determined using molecular replacement, with the structure of plastocyanin from poplar as a search model. Successful crystallization was facilitated by site-directed mutagenesis in which residue Gly8 was substituted with Asp. The region around residue 8 was believed to be too mobile for the wild-type protein to form crystals despite extensive screening. The current structure represents the oxidized plastocyanin, copper (II), at low pH (approximately 4.4). In contrast to the similarity in the core region as compared to its poplar counterpart, the structure shows some significant differences in loop regions. The most notable is the large shift of the 59-61 loop where the largest shift is 3.0 A for the C(alpha) atom of Glu59. This results in different patterns of electrostatic potential around the acidic patches for the two proteins.
    Protein Science 11/1998; 7(10):2099-105. · 2.74 Impact Factor
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    ABSTRACT: The unimolecular rate constant for the photoinduced electron-transfer reaction 3Zncyt/pc(II) --> Zncyt+/pc(I) within the electrostatic complex of zinc cytochrome c and spinach cupriplastocyanin is kF. We report the effects on kF of the following factors, all at pH 7.0: 12 single mutations on the plastocyanin surface (Leu12Asn, Leu12Glu, Leu12Lys, Asp42Asn, Asp42Lys, Glu43Asn, Glu59Gln, Glu59Lys, Glu60Gln, Glu60Lys, Gln88Glu, and Gln88Lys), the double mutation Glu59Lys/Glu60Gln, temperature (in the range 273.3-302.9 K), and solution viscosity (in the range 1. 00-116.0 cP) at 283.2 and 293.2 K. We also report the effects of the plastocyanin mutations on the association constant (Ka) and the corresponding free energy of association (DeltaGa) with zinc cytochrome c at 298.2 K. Dependence of kF on temperature yielded the activation parameters DeltaH, DeltaS, and DeltaG. Dependence of kF on solution viscosity yielded the protein friction and confirmed the DeltaG values determined from the temperature dependence. The aforementioned intracomplex reaction is not a simple electron-transfer reaction because donor-acceptor electronic coupling (HAB) and reorganizational energy (lambda), obtained by fitting of the temperature dependence of kF to the Marcus equation, deviate from the expectations based on precedents and because kF greatly depends on viscosity. This last dependence and the fact that certain mutations affect Ka but not kF are two lines of evidence against the mechanism in which the electron-transfer step is coupled with the faster, but thermodynamically unfavorable, rearrangement step. The electron-transfer reaction is gated by the slower, and thus rate determining, structural rearrangement of the diprotein complex; the rate constant kF corresponds to this rearrangement. Isokinetic correlation of DeltaH and DeltaS parameters and Coulombic energies of the various configurations of the Zncyt/pc(II) complex consistently show that the rearrangement is a facile configurational fluctuation of the associated proteins, qualitatively the same process regardless of the mutations in plastocyanin. Correlation of kF with the orientation of the cupriplastocyanin dipole moment indicates that the reactive configuration of the diprotein complex involves the area near the residue 59, between the upper acidic cluster and the hydrophobic patch. Kinetic effects and noneffects of plastocyanin mutations show that the rearrangement from the initial (docking) configuration, which involves both acidic clusters, to the reactive configuration does not involve the lower acidic cluster and the hydrophobic patch but involves the upper acidic cluster and the area near the residue 88.
    Biochemistry 06/1998; 37(26):9557-69. · 3.38 Impact Factor
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    ABSTRACT: Six different spinach plastocyanin mutants have been constructed by site-directed mutagenesis and expressed in Escherichia coli to probe the importance of the two acidic patches in the interaction with photosystem I. The mutants were: Asp42Lys, Glu43Asn, Glu43Lys, Glu43Gln/Asp44Asn, Glu59Lys/Glu60Gln and Glu43Asn/Glu59Lys/Glu60Gln and they have been characterised by optical absorption and EPR spectroscopy, redox titrations and isoelectric focusing. The electron transfer to photosystem I was investigated by flash-induced time-resolved absorption measurements at 830 nm. The kinetics were interpreted with a model that incorporates a rate-limiting conformational change from inactive to active forms of the plastocyanin-photosystem I complex. All mutations resulted in a displacement of the equilibrium towards the inactive conformation. The strongest impairment of the electron transfer was found for mutations in the larger acidic patch, in particular upon modification of residues 43 or 44. However, mutations of residues 59 and 60 in the smaller acidic patch also resulted in a lower reactivity.
    Biochimica et Biophysica Acta 01/1998; 1322(2-3):106-14. · 4.66 Impact Factor
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    K Sigfridsson, S Young, O Hansson
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    ABSTRACT: Two distinct regions of plastocyanin, one hydrophobic and one acidic, are generally thought to be involved in the electron-transfer reactions with its physiological partners, cytochrome f and photosystem 1. To probe the importance of the hydrophobic patch in the reaction with photosystem 1, seven mutant plastocyanin proteins have been constructed with the following mutations: Gly7Ala, Gly8Asp, Ser11Asp, Ser11Gly, Pro36Gly, Ser85Thr and Gln88Asn. The electron-transfer reaction was investigated by transient flash-photolysis absorption spectroscopy. All proteins remained active in photosystem 1 reduction, showing a biphasic reaction. However, the substitution in position 36 resulted in a drastic decrease in efficiency, suggesting that this residue is involved in a specific contact with photosystem 1. Measurements over a wide range of plastocyanin concentration, ionic strength and pH, showed different properties for the two kinetic phases. A mechanism involving a rate-limiting conformational change accounts well for the observations. Electron transfer from plastocyanin to photosystem 1 would thus require a conversion from an inactive to an active conformation of the complex. Both hydrophobic and electrostatic interactions are important in the dynamics. The structural integrity of a few critical residues, including Pro36, is essential for efficient photosystem 1 reduction.
    European Journal of Biochemistry 06/1997; 245(3):805-12. · 3.58 Impact Factor
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    ABSTRACT: We study, by flash kinetic spectrophotometry on the microsecond time scale, the effects of ionic strength and viscosity on the kinetics of oxidative quenching of the triplet state of zinc cytochrome c (3Zncyt) by the wild-type form and the following nine mutants of cupriplastocyanin: Leu12Glu, Leu12Asn, Phe35Tyr, Gln88Glu, Tyr83Phe, Tyr83His, Asp42Asn, Glu43Asn, and the double mutant Glu59Lys/Glu60Gln. The unimolecular rate constants for the quenching reactions within the persistent diprotein complex, which predominates at low ionic strengths, and within the transient diprotein complex, which is involved at higher ionic strengths, are equal irrespective of the mutation. Evidently, the two complexes are the same. In both reactions, the rate-limiting step is rearrangement of the diprotein complex from a configuration optimal for docking to the one optimal for the subsequent electron-transfer step, which is fast. We investigate the effects of plastocyanin mutations on this rearrangement, which gates the overall electron-transfer reaction. Conversion of the carboxylate anions into amide groups in the lower acidic cluster (residues 42 and 43), replacement of Tyr83 with other aromatic residues, and mutations in the hydrophobic patch in plastocyanin do not significantly affect the rearrangement. Conversion of a pair of carboxylate anions into a cationic and a neutral residue in the upper acidic cluster (residues 59 and 60) impedes the rearrangement. Creation of an anion at position 88, between the upper acidic cluster and the hydrophobic patch, facilitates the rearrangement. The rate constant for the rearrangement smoothly decreases as the solution viscosity increases, irrespective of the mutation. Fittings of this dependence to the modified Kramers's equation and to an empirical equation show that zinc cytochrome c follows the same trajectory on the surfaces of all the plastocyanin mutants but that the obstacles along the way vary as mutations alter the electrostatic potential. Mutations that affect protein association (i.e., change the binding constant) do not necessarily affect the reaction between the associated proteins (i.e., the rate constant) and vice versa. All of the kinetic and thermodynamic effects and noneffects of mutations consistently indicate that in the protein rearrangement the basic patch of zinc cytochrome c moves from a position between the two acidic clusters to a position at or near the upper acidic cluster.
    Biochemistry 01/1997; 35(51):16465-74. · 3.38 Impact Factor
  • Progress in Biophysics and Molecular Biology 01/1996; 65. · 2.91 Impact Factor
  • Kalle Sigfridsson, Simon Young, Örjan Hansson
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    ABSTRACT: A series of plastocyanin mutants have been constructed by site-directed mutagenesis and expressed in Escherichia coli to elucidate the interaction between plastocyanin and photosystem 1 in the photosynthetic electron-transfer chain. Leu-12 has been replaced with alanine, asparagine, glutamate, and lysine, while Tyr-83 has been exchanged for histidine, phenylalanine, and leucine. Phe-35, Asp-42, and Gln-88 have been mutated to tyrosine, asparagine, and glutamate, respectively. The mutations that have been introduced do not seem to place any strain on the tertiary structure according to optical absorption and electron paramagnetic resonance (EPR) spectroscopic studies. However, there are changes in the reduction potential for the Leu-12 mutants that cannot be accounted for by electrostatic interactions alone. For some of the mutants, the pI shifts, in accordance with the changes in the number of titratable groups. Only the Leu-12 mutants show any major change in their photosystem 1 kinetics, while the mutants in the acidic patch show minor changes, suggesting that both the hydrophobic and acidic patches make contact with photosystem 1 but that the electron transfer occurs at the hydrophobic interface, most probably via the His-87 residue. The kinetics are best described with a model in which a rate-limiting conformational change occurs in the plastocyanin-photosystem 1 complex [Bottin, H., & Mathis, P. (1985) Biochemistry 24, 6453-6460; Sigfridsson, K., Hansson, O., Karlsson, B.G., Baltzer L., Nordling, M., & Lundberg, L. G. (1995) Biochim. Biophys. Acta 1228, 28-36], where the changes observed are attributed to changes in the dynamics within the electron-transfer complex.
    Biochemistry 01/1996; 35(4):1249-57. · 3.38 Impact Factor
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    ABSTRACT: Flash-induced voltage changes (electrogenic events) in photosystem I particles from spinach, oriented in a phospholipid layer, have been studied at room temperature on a time scale ranging from 1 micros to several seconds. A phospholipid layer containing photosystem I particles was adsorbed to a Teflon film separating two aqueous compartments. Voltage changes were measured across electrodes immersed in the compartments. In the absence of added electron donors and acceptors, a multiphasic voltage increase, associated with charge separation, was followed by a decrease, associated with charge recombination. Several kinetic phases were resolved: a rapid (<1 micros) increase, ascribed to electron transfer from the primary electron donor P700 to the iron-sulfur electron acceptor FB, was followed by a slower, biphasic increase with time constants of 30 and 200 micros. The 30-micros phase is assigned to electron transfer from FB to the iron-sulfur center FA. The voltage decrease had a time constant of 90 ms, ascribed to charge recombination from FA to P700. Upon chemical prereduction of FA and FB the 30- and 200-micros phases disappeared and the decay time constant was accelerated to 330 micros, assigned to charge recombination from the phylloquinone electron acceptor (A1) or the iron-sulfur center FX to P700.
    Proceedings of the National Academy of Sciences 04/1995; 92(8):3458-62. · 9.81 Impact Factor
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    ABSTRACT: Tyrosine-83 in spinach plastocyanin (Pc) has been modified by site-directed mutagenesis to a histidine. An NMR titration yields a pK value of 8.44 for this residue. The high value is probably due to the acidic residues close to this site. The reduction potential is increased by 35 mV at pH 7.5, but only slightly, if at all, at pH 8.9. EPR and optical absorption bands associated with the copper site are not affected by the mutation, either at pH 7.5 or at pH 8.9. The electron transfer (ET) to Photosystem I (PS I), as studied by a flash-photolysis technique, is pH dependent for the mutant, being slower than the wild type at pH 7.5 but more similar to it at pH 8.9. The data have been interpreted with a model that includes a rate-limiting conformational change in the Pc-PS I complex which precedes the intracomplex ET (Bottin, H. and Mathis, P. (1985) Biochemistry 24, 6453–6460). The slower kinetics at the lower pH for the mutant is attributed to a dual effect of the protonation of the His-83 residue: (i) A destabilization of the ‘close’ bound conformation, i.e., the one competent in electron transfer, and (ii) a smaller intracomplex ET rate constant, partly due to a smaller driving force for ET. From this it is concluded that the Tyr-83 residue is not a part of the ET pathway to PS I.
    Biochimica Et Biophysica Acta-bioenergetics - BBA-BIOENERGETICS. 01/1995; 1228(1):28-36.
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    ABSTRACT: The reduction of plastocyanin by cytochromes c and f has been investigated with mutants of spinach plastocyanin in which individual, highly conserved surface residues have been modified. These include Leu-12 and Phe-35 in the 'northern' hydrophobic patch and Tyr-83 and Asp-42 in the 'eastern' acidic patch. The differences observed all involved binding rather than the intrinsic rates of electron transfer. The Glu-12 and Ala-12 mutants showed small but significant decreases in binding constant with cytochrome c, even though the cytochrome is not expected to make contact with the northern face of plastocyanin. These results, and small changes in the EPR parameters, suggested that these mutations cause small conformational changes in surface residues on the eastern face of plastocyanin, transmitted through the copper centre. In the case of cytochrome f, the Glu-12 and Ala-12 mutants also bound less strongly, but Leu12Asn showed a marked increase in binding constant, suggesting that cytochrome f can hydrogen bond directly to Asn-12 in the reaction complex. A surprising result was that the kinetics of reduction of Asp42Asn were not significantly different from wild type, despite the loss of a negative charge.
    Biochimica et Biophysica Acta 09/1992; 1102(1):85-90. · 4.66 Impact Factor
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    ABSTRACT: Plastocyanin (Pc) has been modified by site-directed mutagenesis at two separate electron-transfer (ET) sites: Leu-12-Glu at a hydrophobic patch, and Tyr-83-His at an acidic patch. The reduction potential at pH 7.5 is decreased by 26 mV in Pc(Leu-12-Glu) and increased by 35 mV in Pc(Tyr-83-His). The latter mutant shows a 2-fold slower intracomplex ET to photosystem I (PSI) as expected from the decreased driving force. The affinity for PSI is unaffected for this mutant but is drastically decreased for Pc(Leu-12-Glu). It is concluded that the hydrophobic patch is more important for the ET to PSI.
    FEBS Letters 11/1991; 291(2):327-30. · 3.58 Impact Factor
  • B. Kallebring, Örjan Hansson
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    ABSTRACT: Photosynthetic organisms absorb solar energy using chlorophyll-containing antennas and convert it to chemical energy in the form of charge-separated radical pairs. Experimental studies of photosystem 2 from plants and cyanobacteria are often interpreted in terms of a model in which the excited antenna is in equilibrium with the charge-separated states. Assigning a single state for the excited antenna is a simplification since it is known that the excitation energy migrates over the antenna for some time until it is trapped in special reaction centers where charge separation takes place. In the present work, existing random-walk models for excitation-energy transfer are extended to a case where charge recombination is allowed for. The treatment is based on Laplace and discrete Fourier transform techniques. It is shown that the simple equilibrium model approximates the situation well, provided that the overall trapping and detrapping rates are appropriately scaled to the rate constants for charge separation and recombination in the reaction center. Expressions for the quantum yields of charge separation and of fluorescence are derived and the consistency between the present random-walk model and the general notion of antenna entropy is demonstrated.
    Chemical Physics 01/1991; 149(3):361-372. · 1.96 Impact Factor
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    ABSTRACT: The reduction rate of P680+, the oxidized form of the primary electron donor of Photosystem II, has been studied with flash absorption spectroscopy at 830 nm. Photosystem II membranes, partially depleted of the intrinsic managanese of the oxygen-evolving complex, were used. The reduction rate of P680+ was measured as a function of the concentration of free Mn2+, which was stabilized by metal-ion buffer systems consisting of chelators and metal-chelator complexes. Increasing the Mn2+ concentration induced an 18 to 35 μs decay component in the P680+ reduction kinetics and diminished the amplitude of the 4 to 8 μs decay component. A dissociation constant of approx. 50 μM was obtained for the observed Mn2+ binding site. Other transition metal ions affected the reduction kinetics of P680+ at lower concentrations. Thus, photooxidation of Mn2+ is not required for the detection of its binding at this site. To account for the kinetic effect, it is proposed that the bound metal ion interacts electrostatically with the tyrosine residue YZ, the intrinsic electron donor to P680+.
    Biochimica et Biophysica Acta (BBA) - Bioenergetics. 01/1991;
  • O Hansson, T Wydrzynski
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    ABSTRACT: In the last few years our knowledge of the structure and function of Photosystem II in oxygen-evolving organisms has increased significantly. The biochemical isolation and characterization of essential protein components and the comparative analysis from purple photosynthetic bacteria (Deisenhofer, Epp, Miki, Huber and Michel (1984) J Mol Biol 180: 385-398) have led to a more concise picture of Photosystem II organization. Thus, it is now generally accepted that the so-called D1 and D2 intrinsic proteins bind the primary reactants and the reducing-side components. Simultaneously, the nature and reaction kinetics of the major electron transfer components have been further clarified. For example, the radicals giving rise to the different forms of EPR Signal II have recently been assigned to oxidized tyrosine residues on the D1 and D2 proteins, while the so-called Q400 component has been assigned to the ferric form of the acceptor-side iron. The primary charge-separation has been meaured to take place in about 3 ps. However, despite all recent major efforts, the location of the manganese ions and the water-oxidation mechanism still remain largely unknown. Other topics which lately have received much attention include the organization of Photosystem II in the thylakoid membrane and the role of lipids and ionic cofactors like bicarbonate, calcium and chloride. This article attempts to give an overall update in this rapidly expanding field.
    Photosynthesis Research 02/1990; 23(2):131-62. · 3.15 Impact Factor
  • Kimiyuki Satoh, Örjan Hansson, Paul Mathis
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    ABSTRACT: Flash-induced absorbance changes in the nanosecond to millisecond time ranges have been measured in the Photosystem II reaction center complex consisting of D1 and D2 subunits and cytochrome b-559, in the presence of 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB). The results indicate that DBMIB largely quenches the primary radical pair (P-680+ Pheo−) and the formation of the triplet (3P-680). Long-lived absorption signals in the red and near-infrared (bleaching at 680 nm and broad increase at 740–830 nm) and in the green (peak at 560 nm) can be attributed to the oxidation of P-680 and to the reduction of cytochrome b-559. These data show that addition of DBMIB induces stabilization of P-680+ and a rapid (perhaps submicrosecond) reduction of cytochrome b-559. The signals attributed to P-680+ and to reduced cytochrome decay in parallel (), showing that the cytochrome reduces P-680+. The stabilization occurred also in the presence of plastoquinone-3 and (with DBMIB) at −29°C in a viscous solution containing 60% glycerol at a low concentration of quinone, suggesting that the quinone reconstitutes the function of QA and thus mediates electron transport from the reduced pheophytin a to the intrinsic cytochrome.
    Biochimica et Biophysica Acta (BBA) - Bioenergetics. 01/1990;
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    P MATHIS, K SATOH, Ö. Hansson
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    ABSTRACT: (D1,D2) Photosystem II reaction centers were studied by flash absorption spectroscopy with microsecond resolution. Without addition, absorption transients in the 660–850 nm region are due to a triplet state, probably of P-680, with a decay half-time of 700 μs (no oxygen) or 40 μs (under air). With the addition of DBMIB, presumably acting as electron acceptor, new kinetic and spectral features appear, which are attributed to P-680. A 5 μs phase of decay is present, which is pH-dependent and is attributed to donation from Z to P-680+.
    FEBS Letters 07/1989; 251:241-244. · 3.58 Impact Factor
  • Harry A. Frank, Örjan Hansson, Paul Mathis
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    ABSTRACT: Electron paramagnetic resonance (EPR) and absorption spectroscopy have been used to study the low temperature photochemical behavior of the Photosystem II D-1/D-2/ cytochrome b559 reaction center complex. The reaction center displays large triplet state EPR signals which are attenuated after actinic illumination at low temperatures in the presence of sodium dithionite. Concomitant with the triplet attenuation is the buildup of a structured radical signal with an effective g value of 2.0046 and a peak-to-peak width of 11.9 G. The structure in the signal is suggestive of it being comprised in part of the anion radical of pheophytin a. This assignment is corroborated by low temperature optical absorbance measurements carried out after actinic illumination at the low temperatures which show absorption bleachings at 681 nm, 544 nm and 422 nm and an absorbance buildup at 446 nm indicating the formation of reduced pheophytin.
    Photosynthesis Research 05/1989; 20(3):279-289. · 3.15 Impact Factor
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    ABSTRACT: The chemical nature of electron donor(s) in photosystem II in photosynthetic membranes was analyzed by site-directed mutagenesis of the gene encoding the protein D2 of the photosystem II reaction center. Mutation of the Tyr-160 residue of the D2 protein into phenylalanine results in the disappearance of the electron paramagnetic resonance signal II(S) originating from D(+), the oxidized form of the slow photosystem II electron donor D. Signal II(S) is still present if a neighboring residue in D2, Met-159, is mutated into arginine. Both mutants have normal rereduction kinetics of the oxidized primary electron donor, P680(+), in octyl glucoside-extracted thylakoids, indicating that D is not directly involved in P680(+) reduction. However, overall photosystem II activity appears to be impaired in the Tyr-160-Phe mutant: photosystem II-dependent growth of this mutant is slowed down by a factor of 3-4, whereas photoheterotrophic growth rates in wild type and mutant are essentially identical. Binding studies of diuron, a photosystem II herbicide, show that there is no appreciable decrease in the number of photosystem II centers in the Tyr-160-Phe mutant. The decrease in photosystem II activity in this mutant may be interpreted to indicate a role of D in photoactivation, rather than one as an important redox intermediate in the photosynthetic electron-transport chain.
    Proceedings of the National Academy of Sciences 12/1988; 85(22):8477-81. · 9.81 Impact Factor

Publication Stats

501 Citations
88.59 Total Impact Points

Institutions

  • 1989–1997
    • Chalmers University of Technology
      • Division of Chemical Physics
      Göteborg, Vaestra Goetaland, Sweden
    • University of Connecticut
      • Department of Chemistry
      Storrs, CT, United States
  • 1988
    • Arizona State University
      Phoenix, Arizona, United States