title: Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors.
abstract: The reduction kinetics of the photo-oxidized primary electron donor P700in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P700, secondary quinone acceptor A1, iron-sulfur clusters and external electron donor and acceptors - methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl2NQ) and oxygen. PS I complexes containing various quinones in the A1-binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl2NQ) as well as FX-core complexes, depleted of terminal iron-sulfur FA/FBclusters, were studied. The acceleration of charge recombination in FX-core complexes by PhQ/PQ substitution indicates that backward ET from the iron-sulfur clusters involves quinone in the A1-binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P700+reduction with the kinetic model. The free energy gap ΔG0between FXand FA/FBclusters was estimated as -130 meV. The driving force of ET from A1to FXwas determined as -50 and -220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A1A-site, this reaction was found to be endergonic (ΔG0= +75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis-Menten kinetics. The second-order rate constants of ET from FA/FB, FXand Cl2NQ in the A1-site of PS I to external acceptors were estimated. The side production of superoxide radical in the A1-site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.
authors.affiliation: A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia.
authors.forename: Georgy E
authors.initials: GE
authors.lastname: Milanovsky
authors.affiliation: A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia.
authors.forename: Anastasia A
authors.initials: AA
authors.lastname: Petrova
authors.affiliation: A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia. cherepanov@belozersky.msu.ru.|A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia. cherepanov@belozersky.msu.ru.
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Cherepanov
authors.affiliation: A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia. semenov@genebee.msu.ru.|N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia. semenov@genebee.msu.ru.
authors.forename: Alexey Yu
authors.identifier: http://orcid.org/0000-0003-1035-0381
authors.initials: AY
authors.lastname: Semenov
mesh_terms: D001665:Binding Sites; D004579:Electron Transport; D004583:Electrons; D007700:Kinetics; D008958:Models, Molecular; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism*; D010971:Plastoquinone / Q000737:chemistry / Q000378:metabolism; D011809:Quinones / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D045331:Photosystem I Protein Complex; D011809:Quinones; D010971:Plastoquinone
keywords: Electron transfer; External electron acceptor; Kinetic modeling; Midpoint redox potentials; Photosystem I; Superoxide radical production