Cofactor X of photosynthetic water oxidation: electron transfer, proton release, and electrogenic behaviour in chloride-depleted Photosystem II

Hundelt, Monika; Haumann, Michael; Junge, Wolfgang

doi:10.1016/s0005-2728(97)00042-x

Cited by 14 publications

(22 citation statements)

References 53 publications

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“…The discrimination between 'chemical' and 'electrostatic' proton liberation is straightforward in the case of figure 1a (third flash). By kinetic and isotopic analyses we have found 'chemical' proton liberation not only upon transition of S 3 ⇒ S 4 → S 0 (Fö rster & Junge 1985;Haumann & Junge 1994a) but also on S 2 ⇒ S 3 Hundelt et al 1997), and possibly (but for technical reasons this is less well defined) also on S 0 ⇒ S 1 . This has led us to a pattern of the intrinsic proton production that is 1 : 0 : 1 : 2 over the four transitions from S 0 ⇒ S 1 to S 3 ⇒ S 4 → S 0 (Haumann & Junge 1999b).…”

Section: Kinetic Properties Of Proton Transfer At the Donor Side Of Psii As A Function Of The Flash Number Monitored By Added Ph-indicatimentioning

confidence: 92%

“…Less obvious to inspection by the eye but discernible by its longer rise time (some 100 s) and a greater kinetic H/D-isotope effect is the chemical release upon S 2 ⇒ S 3 Hundelt et al 1997). In both cases the comparatively slow rises coincide with the rise of the electron transfer to Y ox Z .…”

Section: Kinetic Properties Of Proton Transfer At the Donor Side Of Pmentioning

confidence: 97%

“…The 'chemical' proton release during the transition S 3 ⇒ S 4 → S 0 as detected upon the third flash in figure 1a (half-rise in 1.4 ms) is kinetically distinct from its 'electrostatic' precursor (some 10 s). Less obvious to inspection by the eye but discernible by its longer rise time (some 100 s) and a greater kinetic H/D-isotope effect is the chemical release upon S 2 ⇒ S 3 Hundelt et al 1997). In both cases the comparatively slow rises coincide with the rise of the electron transfer to Y ox Z .…”

Section: Kinetic Properties Of Proton Transfer At the Donor Side Of Psii As A Function Of The Flash Number Monitored By Added Ph-indicatimentioning

confidence: 97%

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Electrostatics and proton transfer in photosynthetic water oxidation

Junge

Haumann

Ahlbrink

et al. 2002

Phil. Trans. R. Soc. Lond. B

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129

131

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Photosystem II (PSII) oxidizes two water molecules to yield dioxygen plus four protons. Dioxygen is released during the last out of four sequential oxidation steps of the catalytic centre (S 0 ⇒ S 1 , S 1 ⇒ S 2 , S 2 ⇒ S 3 , S 3 ⇒ S 4 → S 0 ). The release of the chemically produced protons is blurred by transient, highly variable and electrostatically triggered proton transfer at the periphery (Bohr effect). The extent of the latter transiently amounts to more than one H ϩ /e Ϫ under certain conditions and this is understood in terms of electrostatics. By kinetic analyses of electron-proton transfer and electrochromism, we discriminated between Bohr-effect and chemically produced protons and arrived at a distribution of the latter over the oxidation steps of 1 : 0 : 1 : 2. During the oxidation of tyr-161 on subunit D1 (Y Z ), its phenolic proton is not normally released into the bulk. Instead, it is shared with and confined in a hydrogenbonded cluster. This notion is difficult to reconcile with proposed mechanisms where Y Z acts as a hydrogen acceptor for bound water. Only in manganese (Mn) depleted PSII is the proton released into the bulk and this changes the rate of electron transfer between Y Z and the primary donor of PSII P ϩ 680 from electron to proton controlled. D1-His190, the proposed centre of the hydrogen-bonded cluster around Y Z , is probably further remote from Y Z than previously thought, because substitution of D1-Glu189, its direct neighbour, by Gln, Arg or Lys is without effect on the electron transfer from Y Z to P

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Section: Kinetic Properties Of Proton Transfer At the Donor Side Of Psii As A Function Of The Flash Number Monitored By Added Ph-indicatimentioning

confidence: 92%

Section: Kinetic Properties Of Proton Transfer At the Donor Side Of Pmentioning

confidence: 97%

Section: Kinetic Properties Of Proton Transfer At the Donor Side Of Psii As A Function Of The Flash Number Monitored By Added Ph-indicatimentioning

confidence: 97%

See 1 more Smart Citation

Electrostatics and proton transfer in photosynthetic water oxidation

Junge

Haumann

Ahlbrink

et al. 2002

Phil. Trans. R. Soc. Lond. B

Self Cite

129

131

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“…(3) The oxidation of Y Z causes proton release into the bulk (9,(25)(26)(27)(28). Items 2 and 3 are highly debatable.…”

mentioning

confidence: 99%

“…The new estimates range now between 8.6 and 11.5 Å (24). Moreover, the other paramagnet may not be Mn but an organic radical (component X) (9,(30)(31)(32). The proton that appears in the medium upon formation of Y Z ox in oxygen-eVolVing PSII does not originate from the tyrosine itself but from peripheral amino acid groups which electrostatically interact with the charge residing transiently on Y Z ox and thereafter on the Mn cluster ((33)…”

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confidence: 99%

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

1998

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In oxygen-evolving photosystem II (PSII), a tyrosine residue, D1Tyr161 (Y Z ), serves as the intermediate electron carrier between the catalytic Mn cluster and the photochemically active chlorophyll moiety P 680 . A more direct catalytic role of Y Z , as a hydrogen abstractor from bound water, has been postulated. That Y Z ox appears as a neutral (i.e. deprotonated) radical, Y Z • , in EPR studies is compatible with this notion. Data based on electrochromic absorption transients, however, are conflicting because they indicate that the phenolic proton remains on or near to Y Z ox . In Mn-depleted PSII the electron transfer between Y Z and P 680 + can be almost as fast as in oxygen-evolving material, however, only at alkaline pH. With an apparent pK of about 7 the fast reaction is suppressed and converted into an about 100-fold slower one which dominates at acid pH. In the present work we investigated the optical difference spectra attributable to the transition Y Z f Y Z ox as function of the pH. We scanned the UV and VIS range and used Mn-depleted PSII core particles and also oxygen-evolving ones. Comparing these spectra with published in vitro and in vivo spectra of phenolic compounds, we arrived at the following conclusions: In oxygen-evolving PSII Y Z resembles a hydrogen-bonded tyrosinate, Y Z (-) ‚‚‚H (+) ‚B. The phenolic proton is shifted toward a base B already in the reduced state and even more so in the oxidized state. The retention of the phenolic proton in a hydrogen-bonded network gives rise to a positive net charge in the immediate vicinity of the neutral radical Y Z • . It may be favorable both for the very rapid reduction by Y Z of P 680 + and for electron (not hydrogen) abstraction by Y Z • from the Mn-water cluster.Photosystem II (PSII) 1 produces molecular oxygen from water. It is located in photosynthetic membranes of plants and cyanobacteria. The inner core of PSII is a heterodimer of the D1D2 subunits which show homology with the L and M subunits of the purple bacterial RC (1). The primary electron donor of PSII, P 680 , is located close to the lumenal side of the membrane. The absorption of a quantum of light drives the charge separation between P 680 and the quinone acceptor at the stromal side (2). The very high redox potential of P 680 + drives water oxidation. It is a four-stepped process with at least four increasingly oxidized, metastable states S 0 to S 3 , plus a transient state S 4 that decays in milliseconds into S 0 under release of O 2 . P 680 + is reduced (in nanoseconds) by a redox-active tyrosine residue, Y Z (D1Tyr161 (3, 4)). Y Z ox is, in turn, reduced in microseconds by the oxygenevolving complex (OEC). The structure and exact location of the OEC is still ill-defined. It is formed by four manganese atoms (5, 6), possibly another redox cofactor, X (7-9), plus at least one Cl -ion (10) and one Ca 2+ (11, 12) ion. These cofactors serve various functions during water oxidation: The Mn cluster stores at least two of the oxidizing equivalents (namely on transitions S ...

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Protons, proteins and ATP

Junge

Discoveries in Photosynthesis

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Cofactor X of photosynthetic water oxidation: electron transfer, proton release, and electrogenic behaviour in chloride-depleted Photosystem II

Cited by 14 publications

References 53 publications

Electrostatics and proton transfer in photosynthetic water oxidation

Electrostatics and proton transfer in photosynthetic water oxidation

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

Protons, proteins and ATP

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