### Abstract

Light activation of photosystem I (PS I) induces electron transfer from the excited primary electron donor P700 (a special pair of chlorophyll a/a′ molecules) to three iron-sulfur clusters, F
_{X}
, F
_{A}
, and F
_{B}
via acceptors A
_{O}
(a monomeric chlorophyll a) and A
_{1}
(phylloquinone). PS I complexes isolated from menA and menB mutants contain plastoquinone-9 rather than phylloquinone in the A
_{1}
site and show altered rates of forward electron transfer from A
_{1}
^{-}
to [F
_{A}
/F
_{B}
] and altered rates of back electron transfer from [F
_{A}
/F
_{B}
]
^{-}
to P700
^{+}
(Semenov, A. Y., et al., J. Biol. Chem. 275:23429-23438, 2000). To identify the modified electron transfer steps, we studied the kinetics of flash-induced P700
^{+}
reduction in PS I that contains either an intact set or a subset of iron-sulfur clusters F
_{X}
, F
_{A}
, and F
_{B}
and with the A
_{1}
binding site occupied by phylloquinone or plastoquinone-9. A modeling of the forward and backward electron transfer kinetics in P700-F
_{A}
/F
_{B}
complexes, P700-F
_{X}
cores, and P700-A
_{1}
cores shows that the replacement of phylloquinone by plastoquinone-9 induces a decrease in the free energy gap between A
_{1}
and F
_{A}
/F
_{B}
from ∼-205 mV in wild-type PS I to ∼-70 mV in menA PS I. The +135 mV increase in the midpoint potential of A
_{1}
explains the acceleration in the rate of P700
^{+}
dark reduction in menA PS I, and the resulting uphill electron transfer from A
_{1}
to F
_{X}
in menA PS I explains the absence of a contribution from F
_{X}
^{-}
to the reduction of P700
^{+}
. This fully quantitative description of PS I relates electron transfer rates, equilibrium constants, and redox potentials, and can be used to predict changes in these parameters upon substitution of electron transfer cofactors.

Original language | English (US) |
---|---|

Pages (from-to) | 2885-2897 |

Number of pages | 13 |

Journal | Biophysical journal |

Volume | 83 |

Issue number | 6 |

DOIs | |

State | Published - Dec 1 2002 |

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### All Science Journal Classification (ASJC) codes

- Biophysics

### Cite this

^{+}charge recombination kinetics with phylloquinone and plastoquinone-9 in the A

_{1}site of photosystem I

*Biophysical journal*,

*83*(6), 2885-2897. https://doi.org/10.1016/S0006-3495(02)75298-3

}

^{+}charge recombination kinetics with phylloquinone and plastoquinone-9 in the A

_{1}site of photosystem I ',

*Biophysical journal*, vol. 83, no. 6, pp. 2885-2897. https://doi.org/10.1016/S0006-3495(02)75298-3

**
Modeling of the P700
^{+}
charge recombination kinetics with phylloquinone and plastoquinone-9 in the A
_{1}
site of photosystem I
.** / Shinkarev, Vladimir P.; Zybailov, Boris; Vassiliev, Ilya R.; Golbeck, John H.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Modeling of the P700 + charge recombination kinetics with phylloquinone and plastoquinone-9 in the A 1 site of photosystem I

AU - Shinkarev, Vladimir P.

AU - Zybailov, Boris

AU - Vassiliev, Ilya R.

AU - Golbeck, John H.

PY - 2002/12/1

Y1 - 2002/12/1

N2 - Light activation of photosystem I (PS I) induces electron transfer from the excited primary electron donor P700 (a special pair of chlorophyll a/a′ molecules) to three iron-sulfur clusters, F X , F A , and F B via acceptors A O (a monomeric chlorophyll a) and A 1 (phylloquinone). PS I complexes isolated from menA and menB mutants contain plastoquinone-9 rather than phylloquinone in the A 1 site and show altered rates of forward electron transfer from A 1 - to [F A /F B ] and altered rates of back electron transfer from [F A /F B ] - to P700 + (Semenov, A. Y., et al., J. Biol. Chem. 275:23429-23438, 2000). To identify the modified electron transfer steps, we studied the kinetics of flash-induced P700 + reduction in PS I that contains either an intact set or a subset of iron-sulfur clusters F X , F A , and F B and with the A 1 binding site occupied by phylloquinone or plastoquinone-9. A modeling of the forward and backward electron transfer kinetics in P700-F A /F B complexes, P700-F X cores, and P700-A 1 cores shows that the replacement of phylloquinone by plastoquinone-9 induces a decrease in the free energy gap between A 1 and F A /F B from ∼-205 mV in wild-type PS I to ∼-70 mV in menA PS I. The +135 mV increase in the midpoint potential of A 1 explains the acceleration in the rate of P700 + dark reduction in menA PS I, and the resulting uphill electron transfer from A 1 to F X in menA PS I explains the absence of a contribution from F X - to the reduction of P700 + . This fully quantitative description of PS I relates electron transfer rates, equilibrium constants, and redox potentials, and can be used to predict changes in these parameters upon substitution of electron transfer cofactors.

AB - Light activation of photosystem I (PS I) induces electron transfer from the excited primary electron donor P700 (a special pair of chlorophyll a/a′ molecules) to three iron-sulfur clusters, F X , F A , and F B via acceptors A O (a monomeric chlorophyll a) and A 1 (phylloquinone). PS I complexes isolated from menA and menB mutants contain plastoquinone-9 rather than phylloquinone in the A 1 site and show altered rates of forward electron transfer from A 1 - to [F A /F B ] and altered rates of back electron transfer from [F A /F B ] - to P700 + (Semenov, A. Y., et al., J. Biol. Chem. 275:23429-23438, 2000). To identify the modified electron transfer steps, we studied the kinetics of flash-induced P700 + reduction in PS I that contains either an intact set or a subset of iron-sulfur clusters F X , F A , and F B and with the A 1 binding site occupied by phylloquinone or plastoquinone-9. A modeling of the forward and backward electron transfer kinetics in P700-F A /F B complexes, P700-F X cores, and P700-A 1 cores shows that the replacement of phylloquinone by plastoquinone-9 induces a decrease in the free energy gap between A 1 and F A /F B from ∼-205 mV in wild-type PS I to ∼-70 mV in menA PS I. The +135 mV increase in the midpoint potential of A 1 explains the acceleration in the rate of P700 + dark reduction in menA PS I, and the resulting uphill electron transfer from A 1 to F X in menA PS I explains the absence of a contribution from F X - to the reduction of P700 + . This fully quantitative description of PS I relates electron transfer rates, equilibrium constants, and redox potentials, and can be used to predict changes in these parameters upon substitution of electron transfer cofactors.

UR - http://www.scopus.com/inward/record.url?scp=0036932359&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0036932359&partnerID=8YFLogxK

U2 - 10.1016/S0006-3495(02)75298-3

DO - 10.1016/S0006-3495(02)75298-3

M3 - Article

C2 - 12496065

AN - SCOPUS:0036932359

VL - 83

SP - 2885

EP - 2897

JO - Biophysical Journal

JF - Biophysical Journal

SN - 0006-3495

IS - 6

ER -

^{+}charge recombination kinetics with phylloquinone and plastoquinone-9 in the A

_{1}site of photosystem I Biophysical journal. 2002 Dec 1;83(6):2885-2897. https://doi.org/10.1016/S0006-3495(02)75298-3