Electron transfer from plastocyanin to the photosystem I reaction center in mutants with increased potential of the primary donor in Chlamydomonas reinhardtii

V. M. Ramesh, Mariana Guergova-Kuras, Pierre Joliot, Andrew Webber

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Abstract

The dependence of the P700 +/P700 midpoint potential on kinetics of reduction of P700 + in vivo has been examined in a series of site-directed mutants of Chlamydomonas reinhardtii in which the histidyl axial ligand to the Mg2+ of the P700 chlorophyll a has been changed to several different amino acids. In wild-type photosystem I, the potential of P700 +/P700 is 447 mV and the in vivo half-time of P700 + reduction by its natural donor, plastocyanin, is 4 μs. Substitution of the axial histidine ligand with cysteine increases the potential of P700 +/P700 to 583 mV and changes the rate of P700 + reduction to 0.8 μs. Mutants with a range of potentials between 447 and 583 mV show a strong correlation of the P700 +/P700 potential to the rate of reduction of P700 + by plastocyanin. There is also an increase in the rate of photosystem I-mediated electron transfer from the artificial electron donor DCPIP to methyl viologen in thylakoid membranes. The results indicate that the overall rate constant of P700 + reduction is determined by the rate of electron transfer between the copper and P700 + and confirmed that in vivo there is a preformed complex between plastocyanin and photosystem I. Using approximations of the Marcus electron transfer theory, it is possible to estimate that the distance between the copper of plastocyanin and P700 + is ∼15 Å. On the basis of this distance, the plastocyanin docking site should lie in a 10 Å hollow formed by the lumenal exposed loops between transmembrane helices i and j of PsaA and PsaB.

Original languageEnglish (US)
Pages (from-to)14652-14658
Number of pages7
JournalBiochemistry
Volume41
Issue number50
DOIs
StatePublished - Dec 17 2002

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Plastocyanin
Photosystem I Protein Complex
Chlamydomonas reinhardtii
Electrons
Copper
Ligands
Thylakoids
Paraquat
Histidine
Cysteine
Rate constants
Substitution reactions
Membranes
Amino Acids
Kinetics

ASJC Scopus subject areas

  • Biochemistry

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Electron transfer from plastocyanin to the photosystem I reaction center in mutants with increased potential of the primary donor in Chlamydomonas reinhardtii. / Ramesh, V. M.; Guergova-Kuras, Mariana; Joliot, Pierre; Webber, Andrew.

In: Biochemistry, Vol. 41, No. 50, 17.12.2002, p. 14652-14658.

Research output: Contribution to journalArticle

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title = "Electron transfer from plastocyanin to the photosystem I reaction center in mutants with increased potential of the primary donor in Chlamydomonas reinhardtii",
abstract = "The dependence of the P700 +/P700 midpoint potential on kinetics of reduction of P700 + in vivo has been examined in a series of site-directed mutants of Chlamydomonas reinhardtii in which the histidyl axial ligand to the Mg2+ of the P700 chlorophyll a has been changed to several different amino acids. In wild-type photosystem I, the potential of P700 +/P700 is 447 mV and the in vivo half-time of P700 + reduction by its natural donor, plastocyanin, is 4 μs. Substitution of the axial histidine ligand with cysteine increases the potential of P700 +/P700 to 583 mV and changes the rate of P700 + reduction to 0.8 μs. Mutants with a range of potentials between 447 and 583 mV show a strong correlation of the P700 +/P700 potential to the rate of reduction of P700 + by plastocyanin. There is also an increase in the rate of photosystem I-mediated electron transfer from the artificial electron donor DCPIP to methyl viologen in thylakoid membranes. The results indicate that the overall rate constant of P700 + reduction is determined by the rate of electron transfer between the copper and P700 + and confirmed that in vivo there is a preformed complex between plastocyanin and photosystem I. Using approximations of the Marcus electron transfer theory, it is possible to estimate that the distance between the copper of plastocyanin and P700 + is ∼15 {\AA}. On the basis of this distance, the plastocyanin docking site should lie in a 10 {\AA} hollow formed by the lumenal exposed loops between transmembrane helices i and j of PsaA and PsaB.",
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T1 - Electron transfer from plastocyanin to the photosystem I reaction center in mutants with increased potential of the primary donor in Chlamydomonas reinhardtii

AU - Ramesh, V. M.

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AU - Joliot, Pierre

AU - Webber, Andrew

PY - 2002/12/17

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N2 - The dependence of the P700 +/P700 midpoint potential on kinetics of reduction of P700 + in vivo has been examined in a series of site-directed mutants of Chlamydomonas reinhardtii in which the histidyl axial ligand to the Mg2+ of the P700 chlorophyll a has been changed to several different amino acids. In wild-type photosystem I, the potential of P700 +/P700 is 447 mV and the in vivo half-time of P700 + reduction by its natural donor, plastocyanin, is 4 μs. Substitution of the axial histidine ligand with cysteine increases the potential of P700 +/P700 to 583 mV and changes the rate of P700 + reduction to 0.8 μs. Mutants with a range of potentials between 447 and 583 mV show a strong correlation of the P700 +/P700 potential to the rate of reduction of P700 + by plastocyanin. There is also an increase in the rate of photosystem I-mediated electron transfer from the artificial electron donor DCPIP to methyl viologen in thylakoid membranes. The results indicate that the overall rate constant of P700 + reduction is determined by the rate of electron transfer between the copper and P700 + and confirmed that in vivo there is a preformed complex between plastocyanin and photosystem I. Using approximations of the Marcus electron transfer theory, it is possible to estimate that the distance between the copper of plastocyanin and P700 + is ∼15 Å. On the basis of this distance, the plastocyanin docking site should lie in a 10 Å hollow formed by the lumenal exposed loops between transmembrane helices i and j of PsaA and PsaB.

AB - The dependence of the P700 +/P700 midpoint potential on kinetics of reduction of P700 + in vivo has been examined in a series of site-directed mutants of Chlamydomonas reinhardtii in which the histidyl axial ligand to the Mg2+ of the P700 chlorophyll a has been changed to several different amino acids. In wild-type photosystem I, the potential of P700 +/P700 is 447 mV and the in vivo half-time of P700 + reduction by its natural donor, plastocyanin, is 4 μs. Substitution of the axial histidine ligand with cysteine increases the potential of P700 +/P700 to 583 mV and changes the rate of P700 + reduction to 0.8 μs. Mutants with a range of potentials between 447 and 583 mV show a strong correlation of the P700 +/P700 potential to the rate of reduction of P700 + by plastocyanin. There is also an increase in the rate of photosystem I-mediated electron transfer from the artificial electron donor DCPIP to methyl viologen in thylakoid membranes. The results indicate that the overall rate constant of P700 + reduction is determined by the rate of electron transfer between the copper and P700 + and confirmed that in vivo there is a preformed complex between plastocyanin and photosystem I. Using approximations of the Marcus electron transfer theory, it is possible to estimate that the distance between the copper of plastocyanin and P700 + is ∼15 Å. On the basis of this distance, the plastocyanin docking site should lie in a 10 Å hollow formed by the lumenal exposed loops between transmembrane helices i and j of PsaA and PsaB.

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