Electron transfer reactions in Photosystem II core complexes from Synechococcus at low temperature — difference spectrum of P680+QA−P680 QA at 77 K

Hillmann, B.; Schlodder, E.

doi:10.1016/0005-2728(95)00068-t

Cited by 53 publications

(73 citation statements)

References 48 publications

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“…As mentioned above, the B A + cation would be located over the center and near normal to the P A macrocycle, producing little electrochromic shift. This geometry is inconsistent with an interpretation of the P A derived bleaching at 672.5 nm ( Figure 3) as being part of an electrochromic red-shift (30,54) induced by a positive charge on B A . It is, however, consistent with the localization of the cation on P A accompanied by an electrochromic blue shift of B A as in the bacterial reaction centers (see below).…”

Section: Location Of 3 P As a Function Of Temperaturecontrasting

confidence: 78%

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Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

et al. 2001

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Site-directed mutations were introduced to replace D1-His198 and D2-His197 of the D1 and D2 polypeptides, respectively, of the photosystem II (PSII) reaction center of Synechocystis PCC 6803. These residues coordinate chlorophylls P A and P B which are homologous to the special pair Bchlorophylls of the bacterial reaction centers that are coordinated respectively by histidines L-173 and M-200 (202). P A and P B together serve as the primary electron donor, P, in purple bacterial reaction centers. In PS II, the site-directed mutations at D1 His198 affect the P + -P-absorbance difference spectrum. The bleaching maximum in the Soret region (in WT at 433 nm) is blue-shifted by as much as 3 nm. In the D1 His198Gln mutant, a similar displacement to the blue is observed for the bleaching maximum in the Q y region (672.5 nm in WT at 80 K), whereas features attributed to a band shift centered at 681 nm are not altered. In the Y Z •-Y Z -difference spectrum, the band shift of a reaction center chlorophyll centered in WT at 433-434 nm is shifted by 2-3 nm to the blue in the D1-His198Gln mutant. The D1-His198Gln mutation has little effect on the optical difference spectrum, 3 P-1 P, of the reaction center triplet formed by P + Pheo -charge recombination (bleaching at 681-684 nm), measured at 5-80 K, but becomes visible as a pronounced shoulder at 669 nm at temperatures g150 K. Measurements of the kinetics of oxidized donor-Q A -charge recombination and of the reduction of P + by redox active tyrosine, Y Z , indicate that the reduction potential of the redox couple P + /P can be appreciably modulated both positively and negatively by ligand replacement at D1-198 but somewhat less so at D2-197. On the basis of these observations and others in the literature, we propose that the monomeric accessory chlorophyll, B A , is a long-wavelength trap located at 684 nm at 5 K. B A * initiates primary charge separation at low temperature, a function that is increasingly shared with P A * in an activated process as the temperature rises. Charge separation from B A * would be potentially very fast and form P A + B A -and/or B A + Pheo -as observed in bacterial reaction centers upon direct excitation of B A ) Proc. Natl. Acad Sci. 96, 2054-2059. The cation, generated upon primary charge separation in PSII, is stabilized at all temperatures primarily on P A , the absorbance spectrum of which is displaced to the blue by the mutations. In WT, the cation is proposed to be shared to a minor extent (∼20%) with P B , the contribution of which can be modulated up or down by mutation. The band shift at 681 nm, observed in the P + -P difference spectrum, is attributed to an electrochromic effect of P A + on neighboring B A . Because of its low-energy singlet and therefore triplet state, the reaction center triplet state is stabilized on B A at e80 K but can be shared with P A at >80 K in a thermally activated process.

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Section: Location Of 3 P As a Function Of Temperaturecontrasting

confidence: 78%

“…Low-temperature optical measurements of P + -P and 3 P-1 P were performed on PSII core complexes as previously described (54). Sub-microsecond, flash-induced absorbance changes were measured at room temperature in an instrument described by Béal et al (55).…”

Section: Methodsmentioning

confidence: 99%

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

et al. 2001

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“…As shown in Fig. 5B, the experiment indicates an enhanced oxidation of Chl Z (ϳ1.25 times at 666 nm) (48) in the mutant as compared with WT. Both of these observations indicate a displacement of the Car ϩ Chl Z % CarChl Z ϩ equilibrium to the right in the Pdscap2 mutant, consistent with the presence in the mutant of shorter -conjugated chain carotenoids with higher reduction potentials.…”

Section: Modification Of Carotenoid Biosynthesis Pathway In Synechocymentioning

confidence: 62%

Construction and Characterization of Genetically Modified Synechocystis sp. PCC 6803 Photosystem II Core Complexes Containing Carotenoids with Shorter π-Conjugation than β-Carotene

Bautista

Tracewell

Schlodder

et al. 2005

Journal of Biological Chemistry

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␤-Carotene has been identified as an intermediate in a secondary electron transfer pathway that oxidizes Chl Z and cytochrome b 559 in Photosystem II (PS II) when normal tyrosine oxidation is blocked. To test the redox function of carotenoids in this pathway, we replaced the -carotene desaturase gene (zds) or both the zds and phytoene desaturase (pds) genes of Synechocystis sp. PCC 6803 with the phytoene desaturase gene (crtI) of Rhodobacter capsulatus, producing carotenoids with shorter conjugated -electron systems and higher reduction potentials than ␤-carotene. The PS II core complexes of both mutant strains contain approximately the same number of chlorophylls and carotenoids as the wild type but have replaced ␤-carotene (11 double bonds), with neurosporene (9 conjugated double bonds) and ␤-zeacarotene (9 conjugated double bonds and 1 ␤-ionylidene ring). The presence of the ring appears necessary for PS II assembly. Visible and near-infrared spectroscopy were used to examine the light-induced formation of chlorophyll and carotenoid radical cations in the mutant PS II core complexes at temperatures from 20 to 160 K. At 20 K, a carotenoid cation radical is formed having an absorption maximum at 898 nm, an 85 nm blue shift relative to the ␤-carotene radical cation peak in the WT, and consistent with the formation of the cation radical of a carotenoid with 9 conjugated double bonds. The ratio of Chl ؉ /Car ؉ is higher in the mutant core complexes, consistent with the higher reduction potential for Car ؉ . As the temperature increases, other carotenoids become accessible to oxidation by P 680A carotenoid molecule is an extended polyene chain with a variety of end groups and has been thought of as a "molecular wire," because, in the one-electron oxidized form, or carotenoid radical cation, the hole is delocalized over the entire conjugated -system. Carotenoid radical cations have recently been observed in several photosynthetic pigmentprotein complexes, including PS II, 3 bacterial light-harvesting complexes LHC II, and recently in plant PsbS where they may have a role in non-photochemical energy quenching (1). Among photosynthetic reaction centers, carotenoid photooxidation is unique to PS II, which uses light energy to catalyze the oxidation of water to molecular oxygen. The process of water oxidation involves highly oxidizing species that can also oxidize a carotenoid molecule. Carotenoid radical cations have been identified as intermediates in the secondary electron transport pathway of PS II (2-6).Detergent-solubilized PS II core complexes contain up to 25 different integral membrane and extrinsic polypeptide subunits, including the D1/D2 complex and light-harvesting pigment-protein complexes CP43 (PsbC) and CP47 (PsbB). Light energy is absorbed by the chlorophyll-containing light-harvesting antenna and transferred to the primary donor chlorophyll(s) coordinated by the D1/D2 polypeptides. The term "PS II reaction centers" describes a structure that includes the D1 and D2 polypeptides, cytochrome b 559 (Cyt b ...

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“…When Tyr Z donation is inhibited by lowering the temperature, the charge separated state P680 ? Q A -decays mainly by charge recombination with t 1/2 * 2-5 ms (Butler 1973;Faller et al 2005;Hillmann and Schlodder 1995;Mathis and Vermeglio 1974;Murata et al 1973). Under these conditions the side-path electron donors are able to donate electrons to P680 ?…”

Section: Introductionmentioning

confidence: 98%

“…and these are known as sidepath donors. This secondary pathway includes b-carotene (Car), the heme of the cytochrome b 559 subunit (Cytb 559 ) and a peripheral Chl known as ChlZ (Faller et al 2001;Hanley et al 1999;Hillmann and Schlodder 1995;Tracewell and Brudvig 2003;Tracewell et al 2001), which is reviewed in Faller et al (2005) and Stewart and Brudvig (1998). At physiological temperatures, Tyr Z oxidation greatly out-competes electron donation from the side-path electron donors (Faller et al 2001(Faller et al , 2005Stewart and Brudvig 1998).…”

Section: Introductionmentioning

confidence: 99%

Quantum efficiency distributions of photo-induced side-pathway donor oxidation at cryogenic temperature in photosystem II

et al. 2008

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We monitored illuminated-minus-dark absorption difference spectra in the range of 450-1100 nm induced by continuous illumination at 8 K of photosystem II (PSII) core complexes from Thermosynechococcus elongatus. The photo-induced oxidation of the side-path donors Cytb(559), beta-carotene and chlorophyll Z, as well as the concomitant stable (t(1/2) > 1 s) reduction of the first plastoquinone electron acceptor, Q(A) (monitored by the well-known 'C550' shift), were quantified as a function of the absorbed photons per PSII. The Q(A) photo-induced reduction data can be described by three distinct quantum efficiency distributions: (i) a very high efficiency of approximately 0.5-1, (ii) a middle efficiency with a very large range of approximately 0.014-0.2, and (iii) a low efficiency of approximately 0.002. Each of the observed side-path donors exhibited similar quantum efficiency distributions, which supports a branched pathway model for side-path oxidation where beta-carotene is the immediate electron donor to the photo-oxidized chlorophyll (P680(+)). The yields of the observed side-path donors account quantitatively for the wide middle efficiency range of photo-induced Q(A) reduction, but not for the PSII fractions that exhibit the highest and lowest efficiencies. The high-efficiency component may be due to Tyr(Z) oxidation. A donor that does not exhibit an identified absorption in the visible-near-IR region is mainly responsible for the lowest efficiency component.

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Electron transfer reactions in Photosystem II core complexes from Synechococcus at low temperature — difference spectrum of P680+QA−P680 QA at 77 K

Cited by 53 publications

References 48 publications

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

Construction and Characterization of Genetically Modified Synechocystis sp. PCC 6803 Photosystem II Core Complexes Containing Carotenoids with Shorter π-Conjugation than β-Carotene

Quantum efficiency distributions of photo-induced side-pathway donor oxidation at cryogenic temperature in photosystem II

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