Coordination of proton and electron transfer from the redox-active tyrosine, Yz, of Photosystem II and examination of the electrostatic influence of oxidized tyrosine, YD .(H+)

Bruce A. Diner, James A. Bautista, Peter J. Nixon, Catherine Berthomieu, Rainer Hienerwadel, R. David Britt, Willem Vermaas, Dexter A. Chisholm

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Abstract

The redox active tyrosines, YZ and YD, of Photosystem II are oxidized by P680 + to the neutral radical. Such oxidation requires coupling of electron transfer to the transfer of the phenolic proton. Studies of the multiphasic kinetics of YZ oxidation in Mn-depleted PSII core complexes have shown that the relative amplitudes of the kinetic components are pH-dependent with one component showing a pH-dependent t1/2 in the microsecond to tens of microsecond range (pH 4-8). Sjödin and coworkers (M. Sjödin, S. Styring, B. Akemark, L. Sun and L. Hammarström, Philos. Trans. R. Soc. London. Ser. B, 2002, 357, 1471-1479) have suggested that the increase in rate of this latter component with pH reflects an increase in the driving force of the reaction by lowering the reduction potential of YZ ./ YZ, consistent with concerted electron and proton transfer (CEP mechanism). A similar dependence of the rate of YZ oxidation on ΔG° is reported here through modification of the reduction potential of P680 +/P 680, that is, without modifying either the proton acceptor or the pathway for proton transfer. The results reported here support a CEP mechanism, though formation of the tyrosinate followed by electron transfer cannot be completely ruled out. The presence of oxidized tyrosine YD .(H+) has been shown to accelerate the photoactivation of the oxygen evolving complex, possibly by an increase in the reduction potential of P680 +/ P680. The influence of Y D .(H+) on the P680 +/P680 reduction potential is examined here by measuring the rate of YZ oxidation in Mn-depleted core complexes from the WT strain and from a YD-less strain of Synechocystis 6803. Also examined is the influence of YD .(H+) on the P 680 +-P680 difference spectrum. These comparisons show that the electrostatic contribution of YD .(H+) to the reduction potential of redox couple P 680 +/P680 is very small (≤ 10 mV), implying that the role of YD .(H+) in photoactivation may have more to do with its providing an oxidizing equivalent during assembly of the manganese cluster.

Original languageEnglish (US)
Pages (from-to)4844-4850
Number of pages7
JournalPhysical Chemistry Chemical Physics
Volume6
Issue number20
DOIs
StatePublished - Oct 21 2004

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Photosystem II Protein Complex
tyrosine
Tyrosine
Protons
Electrostatics
electron transfer
examination
electrostatics
protons
Electrons
Oxidation
Proton transfer
oxidation
Kinetics
Manganese
kinetics
Oxidation-Reduction
Oxygen
manganese
assembly

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Atomic and Molecular Physics, and Optics

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Coordination of proton and electron transfer from the redox-active tyrosine, Yz, of Photosystem II and examination of the electrostatic influence of oxidized tyrosine, YD .(H+). / Diner, Bruce A.; Bautista, James A.; Nixon, Peter J.; Berthomieu, Catherine; Hienerwadel, Rainer; Britt, R. David; Vermaas, Willem; Chisholm, Dexter A.

In: Physical Chemistry Chemical Physics, Vol. 6, No. 20, 21.10.2004, p. 4844-4850.

Research output: Contribution to journalArticle

Diner, Bruce A. ; Bautista, James A. ; Nixon, Peter J. ; Berthomieu, Catherine ; Hienerwadel, Rainer ; Britt, R. David ; Vermaas, Willem ; Chisholm, Dexter A. / Coordination of proton and electron transfer from the redox-active tyrosine, Yz, of Photosystem II and examination of the electrostatic influence of oxidized tyrosine, YD .(H+). In: Physical Chemistry Chemical Physics. 2004 ; Vol. 6, No. 20. pp. 4844-4850.
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abstract = "The redox active tyrosines, YZ and YD, of Photosystem II are oxidized by P680 + to the neutral radical. Such oxidation requires coupling of electron transfer to the transfer of the phenolic proton. Studies of the multiphasic kinetics of YZ oxidation in Mn-depleted PSII core complexes have shown that the relative amplitudes of the kinetic components are pH-dependent with one component showing a pH-dependent t1/2 in the microsecond to tens of microsecond range (pH 4-8). Sj{\"o}din and coworkers (M. Sj{\"o}din, S. Styring, B. Akemark, L. Sun and L. Hammarstr{\"o}m, Philos. Trans. R. Soc. London. Ser. B, 2002, 357, 1471-1479) have suggested that the increase in rate of this latter component with pH reflects an increase in the driving force of the reaction by lowering the reduction potential of YZ ./ YZ, consistent with concerted electron and proton transfer (CEP mechanism). A similar dependence of the rate of YZ oxidation on ΔG° is reported here through modification of the reduction potential of P680 +/P 680, that is, without modifying either the proton acceptor or the pathway for proton transfer. The results reported here support a CEP mechanism, though formation of the tyrosinate followed by electron transfer cannot be completely ruled out. The presence of oxidized tyrosine YD .(H+) has been shown to accelerate the photoactivation of the oxygen evolving complex, possibly by an increase in the reduction potential of P680 +/ P680. The influence of Y D .(H+) on the P680 +/P680 reduction potential is examined here by measuring the rate of YZ oxidation in Mn-depleted core complexes from the WT strain and from a YD-less strain of Synechocystis 6803. Also examined is the influence of YD .(H+) on the P 680 +-P680 difference spectrum. These comparisons show that the electrostatic contribution of YD .(H+) to the reduction potential of redox couple P 680 +/P680 is very small (≤ 10 mV), implying that the role of YD .(H+) in photoactivation may have more to do with its providing an oxidizing equivalent during assembly of the manganese cluster.",
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T1 - Coordination of proton and electron transfer from the redox-active tyrosine, Yz, of Photosystem II and examination of the electrostatic influence of oxidized tyrosine, YD .(H+)

AU - Diner, Bruce A.

AU - Bautista, James A.

AU - Nixon, Peter J.

AU - Berthomieu, Catherine

AU - Hienerwadel, Rainer

AU - Britt, R. David

AU - Vermaas, Willem

AU - Chisholm, Dexter A.

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N2 - The redox active tyrosines, YZ and YD, of Photosystem II are oxidized by P680 + to the neutral radical. Such oxidation requires coupling of electron transfer to the transfer of the phenolic proton. Studies of the multiphasic kinetics of YZ oxidation in Mn-depleted PSII core complexes have shown that the relative amplitudes of the kinetic components are pH-dependent with one component showing a pH-dependent t1/2 in the microsecond to tens of microsecond range (pH 4-8). Sjödin and coworkers (M. Sjödin, S. Styring, B. Akemark, L. Sun and L. Hammarström, Philos. Trans. R. Soc. London. Ser. B, 2002, 357, 1471-1479) have suggested that the increase in rate of this latter component with pH reflects an increase in the driving force of the reaction by lowering the reduction potential of YZ ./ YZ, consistent with concerted electron and proton transfer (CEP mechanism). A similar dependence of the rate of YZ oxidation on ΔG° is reported here through modification of the reduction potential of P680 +/P 680, that is, without modifying either the proton acceptor or the pathway for proton transfer. The results reported here support a CEP mechanism, though formation of the tyrosinate followed by electron transfer cannot be completely ruled out. The presence of oxidized tyrosine YD .(H+) has been shown to accelerate the photoactivation of the oxygen evolving complex, possibly by an increase in the reduction potential of P680 +/ P680. The influence of Y D .(H+) on the P680 +/P680 reduction potential is examined here by measuring the rate of YZ oxidation in Mn-depleted core complexes from the WT strain and from a YD-less strain of Synechocystis 6803. Also examined is the influence of YD .(H+) on the P 680 +-P680 difference spectrum. These comparisons show that the electrostatic contribution of YD .(H+) to the reduction potential of redox couple P 680 +/P680 is very small (≤ 10 mV), implying that the role of YD .(H+) in photoactivation may have more to do with its providing an oxidizing equivalent during assembly of the manganese cluster.

AB - The redox active tyrosines, YZ and YD, of Photosystem II are oxidized by P680 + to the neutral radical. Such oxidation requires coupling of electron transfer to the transfer of the phenolic proton. Studies of the multiphasic kinetics of YZ oxidation in Mn-depleted PSII core complexes have shown that the relative amplitudes of the kinetic components are pH-dependent with one component showing a pH-dependent t1/2 in the microsecond to tens of microsecond range (pH 4-8). Sjödin and coworkers (M. Sjödin, S. Styring, B. Akemark, L. Sun and L. Hammarström, Philos. Trans. R. Soc. London. Ser. B, 2002, 357, 1471-1479) have suggested that the increase in rate of this latter component with pH reflects an increase in the driving force of the reaction by lowering the reduction potential of YZ ./ YZ, consistent with concerted electron and proton transfer (CEP mechanism). A similar dependence of the rate of YZ oxidation on ΔG° is reported here through modification of the reduction potential of P680 +/P 680, that is, without modifying either the proton acceptor or the pathway for proton transfer. The results reported here support a CEP mechanism, though formation of the tyrosinate followed by electron transfer cannot be completely ruled out. The presence of oxidized tyrosine YD .(H+) has been shown to accelerate the photoactivation of the oxygen evolving complex, possibly by an increase in the reduction potential of P680 +/ P680. The influence of Y D .(H+) on the P680 +/P680 reduction potential is examined here by measuring the rate of YZ oxidation in Mn-depleted core complexes from the WT strain and from a YD-less strain of Synechocystis 6803. Also examined is the influence of YD .(H+) on the P 680 +-P680 difference spectrum. These comparisons show that the electrostatic contribution of YD .(H+) to the reduction potential of redox couple P 680 +/P680 is very small (≤ 10 mV), implying that the role of YD .(H+) in photoactivation may have more to do with its providing an oxidizing equivalent during assembly of the manganese cluster.

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