CIDEP observations in photosystem I of green plant and algal photosynthesis

McIntosh, Alan R.; Manikowski, H.; Wong, S. K.; Taylor, C. P. S.; Bolton, James R.

doi:10.1016/0006-291x(79)91837-0

Cited by 27 publications

(10 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previous studies on a variety of photosynthetic organisms hav~ given us inform~tion about: the mechanism of the primary electron transfer reactions, t~e ch~mical identity of the species involved in these events [1][2][3][4][5][6], the dynamics of these reactions [7][8][9], and the struitur~l relation and interactions between th~ primary photoreactants.…”

Section: Introductionmentioning

confidence: 99%

Orientation dependence of radical pair interactions in spinach chloroplasts

McCracken

Sauer

1983

Biochimica et Biophysica Acta (BBA) - Bioenergetics

View full text Add to dashboard Cite

Section: Introductionmentioning

confidence: 99%

Orientation dependence of radical pair interactions in spinach chloroplasts

McCracken

Sauer

1983

Biochimica et Biophysica Acta (BBA) - Bioenergetics

View full text Add to dashboard Cite

“…A light-induced EPR signal with characteristic e/a/e polarization (e = emissive, a = absorptive) was observed in PSI a number of years ago (30,31). Yet the identity of this signal remained unclear.…”

Section: Theorymentioning

confidence: 99%

“…A1 has been identified as vitamin K1 (29). Thus, existing information points to the following chain of electron transfer steps, initiated by photoexcitation of the donor P700 (25, 29):A light-induced EPR signal with characteristic e/a/e polarization (e = emissive, a = absorptive) was observed in PSI a number of years ago (30,31). Yet the identity of this signal remained unclear.…”

mentioning

confidence: 99%

Light-generated nuclear quantum beats: a signature of photosynthesis.

Weber

Ohmes²,

Thurnauer³

et al. 1995

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

View full text Add to dashboard Cite

Light-induced radical pairs in deuterated and deuterated plus 15N-substituted Synechococcus lividus cyanobacteria have been studied by transient EPR following pulsed laser excitation. Nuclear quantum beats are observed in the transverse electron magnetization at lower temperatures. Model calculations for the time profiles, evaluated at the high-field emissive maximum of the spectrum, indicate assignment of these coherences to nitrogen nuclei in the primary donor. Thorough investigation of the nuclear modulation patterns can provide detailed information on the electronic structure of the primary donor, providing insight into the mechanism of the primary events of plant photosynthesis. THEORYIn this section we briefly summarize a model for transient EPR of spin-correlated radical pairs and define the model parameters (16, 21-23). Specifically, we consider a sudden lightinduced generation of the radical pair with a spatially fixed geometry. Particular emphasis is given to the nuclear spin interactions, essential for the modeling of nuclear quantum beats.The total spin Hamiltonian, H(fl, t), depends on the orientation, Q, of the radical pair and can be divided into seven parts:H(fQ, t) = Hz(fQ) + HR(fl, t) + HEX + HD(Q)Spin-correlated radical pairs (1-7) are generated as short-lived intermediates in the primary energy conversion steps of natural photosynthesis (1,(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). If the initial configuration of the radical pair is not an eigenstate of the corresponding spin Hamiltonian, the radical pair starts out in a coherent superposition of spin states (15)(16)(17)(18)(19), which can manifest itself as quantum beats in an EPR experiment with adequate time resolution (20)(21)(22)(23)(24). In the following we report transient EPR studies of light-induced radical pairs in plant photosystem I (PSI) with particular reference to nuclear spin coherences generated by a laser pulse. The primary electron transfer process in PSI involves the primary chlorophyll donor P700 and a series of protein-bound acceptors, Ao, A1, Fx, FA, and FB (25). Although the PSI reaction center has been crystallized, its x-ray structure is not known with great detail (26). Yet there is substantial evidence that two chlorophyll molecules, the special pair (27), form the primary donor (26, 28). Furthermore, current evidence suggests that Ao is a chlorophyll species and Fx, FA, and FB are iron-sulfur (FeS) centers. A1 has been identified as vitamin K1 (29). Thus, existing information points to the following chain of electron transfer steps, initiated by photoexcitation of the donor P700 (25, 29):A light-induced EPR signal with characteristic e/a/e polarization (e = emissive, a = absorptive) was observed in PSI a number of years ago (30,31). Yet the identity of this signal remained unclear. Recent work proves a direct assignment of the polarized spectrum to the secondary radical pair, P4o0A-(29, 32). Here we report observation of nuclear quantum beats for P7OAj in deuterated and deuterated plus 15N-substituted Synechococ...

show abstract

“…' Spin polarization has been studied in a wide variety of green plant [1][2][3][4], algal [3][4][5][6] and bacterial [7] preparations using electron paramagnetic resonance lEPR) techniques·at room temperature and at low temperature. All of these studies make use of pulsed light excitation and fast time-resolved EPR to probe the initial charge transfer events of the photosynthetic process.…”

Section: Introductionmentioning

confidence: 99%

“…Our choice of sample ~~' ,: .., co~ditions for this study was based on the current model of the photosystem I reaction center organization, which may be represented as [3,4] for algae and subchloroplast particles. However, if the photosystem I reaction center is poised in the redox state P700 A 1 x-Fd 8 -FdA-prior to the low temperature pulsed-light EPR measurement, a substantial change in both dynamics and spectral lineshape of the observed transient species is observed~ It is possible to interpret these new findings to distinguish between two candidates for the primary acceptor A 1 , which has been attributed to a chlorophyll a monomer [15,16] or a chlorophyll a dimer [17].…”

Section: Introductionmentioning

confidence: 99%