Photooxidation of chlorophyll in spinach chloroplasts between 10 and 180 K

Visser, J. W. M.; Rijgersberg, C.P.; Gast, P.

doi:10.1016/0005-2728(77)90149-9

Cited by 70 publications

(42 citation statements)

References 25 publications

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“…The observation that the chlorophyll cation radical assigned to P680 ÷ has a reduced linewidth compared to the monomeric chlorophyll confirms early studies using chloroplasts or crude PS II particles [24,[26][27][28][29]. In a recent paper, Hoganson and Babcock [30] have shown the width of the P680 + radical, measured kinetically, to be 0.79 mT in the absence of Z ÷.…”

Section: Illumination At Cryogenic Temperaturessupporting

confidence: 76%

“…The spectrum was composed of two parts, a rapidly reversi- ble 0.8 mT radical, as seen with SiMo as acceptor in fig.2A, on top of an essentially irreversible 1.0 mT radical. The 1.0 mT radical is characteristic of an oxidised monomeric chlorophyll a [24]. It should also be noted that a split radical (arrow, fig.3C) increased in parallel with the 1.0 mT radical and may be due to a radical pair interaction [5].…”

Section: Illumination At Cryogenic Temperaturesmentioning

confidence: 89%

“…Previous authors were undecided about P680 being a monomer or dimer of chlorophyll [24,28,29]. The EPR linewidth of dimeric chlorophyll may be narrowed by x/2 as compared to the monomer as found in Rhodobacter sphaeroides [31].…”

Section: Illumination At Cryogenic Temperaturesmentioning

confidence: 96%

“…These probably arise from electron donors, P680 + or another oxidised species such as monomeric chlorophyll or carotenoid [23,24]. For porphyrin radicals, the major interaction of the unpaired electron is with the magnetic nuclei of the macrocycle protons.…”

Section: Illumination At Cryogenic Temperaturesmentioning

confidence: 99%

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Electron transfer in the isolated photosystem II reaction centre complex

Nugent¹,

Telfer²,

Demetriou³

et al. 1989

FEBS Letters

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We have characterised the electron-transfer properties of the D 1/D2/cytochrome b-559 complex using EPR spectrometry. The complex can transfer electrons to silicomolybdate and ferricyanide at cryogenic temperatures. In the presence of silicomolybdate or ferricyanide, two chlorophyll cation radicals were observed from P680 ÷ (0.8 mT) and monomeric Chl (1.0 mT). Reduction of silicomolybdate was detected as a 2.7 mT signal at g = 1.942. A radical attributed to a tyrosine cation radical (D ÷/Z ÷) was also observed in a small percentage of centres.

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Section: Illumination At Cryogenic Temperaturessupporting

confidence: 76%

Section: Illumination At Cryogenic Temperaturesmentioning

confidence: 89%

Section: Illumination At Cryogenic Temperaturesmentioning

confidence: 96%

Section: Illumination At Cryogenic Temperaturesmentioning

confidence: 99%

See 2 more Smart Citations

Electron transfer in the isolated photosystem II reaction centre complex

Nugent¹,

Telfer²,

Demetriou³

et al. 1989

FEBS Letters

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“…1 A and B arrow) in these samples. This magnetic field value is outside the magnetic-field range in which signals from Chl and carotenoid cations could contribute significantly (42,43). Fig.…”

Section: Construction Of D1-y161f Mutants and Isolation Of Psii Partimentioning

confidence: 88%

Rapid formation of the stable tyrosyl radical in photosystem II

Faller

Debus

Brettel

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

119

145

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Two symmetrically positioned redox active tyrosine residues are present in the photosystem II (PSII) reaction center. One of them, TyrZ, is oxidized in the ns-s time scale by P680 ؉ and reduced rapidly (s to ms) by electrons from the Mn complex. The other one, TyrD, is stable in its oxidized form and seems to play no direct role in enzyme function. Here, we have studied electron donation from these tyrosines to the chlorophyll cation (P680 ؉ ) in Mndepleted PSII from plants and cyanobacteria. In particular, a mutant lacking TyrZ was used to investigate electron donation from TyrD. By using EPR and time-resolved absorption spectroscopy, we show that reduced TyrD is capable of donating an electron to P680 ؉ with t 1/2 Ϸ 190 ns at pH 8.5 in approximately half of the centers. This rate is Ϸ10 5 times faster than was previously thought and similar to the TyrZ donation rate in Mn-depleted wild-type PSII (pH 8.5). Some earlier arguments put forward to rationalize the supposedly slow electron donation from TyrD (compared with that from TyrZ) can be reassessed. At pH 6.5, TyrZ (t 1/2 ‫؍‬ 2-10 s) donates much faster to P680 ؉ than does TyrD (t1/2 > 150 s). These different rates may reflect the different fates of the proton released from the respective tyrosines upon oxidation. The rapid rate of electron donation from TyrD requires at least partial localization of P680 ؉ on the chlorophyll (P D2) that is located on the D2 side of the reaction center.T yrosyl radicals play key roles in the mechanisms of a wide range of enzymes. Understanding these roles and how proteins are able to control these reactive species to carry out quite specific chemical reactions has been an important aim of researchers in this area (for review, see ref. 1). One of the earliest demonstrations of redox active tyrosines was in photosystem II (PSII), the water oxidizing enzyme, in which a tyrosyl radical, designated tyrosine Z ⅐ (TyrZ ⅐ ), is thought to play a key role in the active site, abstracting electrons and possibly protons from the substrate water that is bound to the highly oxidized Mn cluster (2-5).PSII contains a second tyrosyl radical, TyrD ⅐ , which is stable during enzyme function and which is located in a 2-fold rotationally symmetrical position to TyrZ on a subunit (D2) adjacent to that (D1) in which water oxidation takes place. TyrZ and TyrD are equally situated relative to the central chlorophyll (Chl) pair (P D1 and P D2 ) with the center-to-center distances for TyrZ-P D1 and TyrD-P D2 being Ϸ12.4 Å (6). It is this pair of Chls that bears the photogenerated cation (P680 ϩ ) that is considered to be the oxidant for the tyrosines (refs. 6-12; for recent reviews see refs. 2 and 3). The existing enzyme may have evolved from an ancestor in which the core was a homodimer with the two tyrosines having identical redox functions (13).Despite homologous positions in subunits D1 and D2, TyrZ and TyrD exhibit extremely different kinetics, different redox potentials, and play completely different functional roles in the enzyme. Thus, they con...

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