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The 2-Methoxy Group Orientation Regulates the Redox Potential Difference between the Primary (QA) and Secondary (QB) Quinones of Type II Bacterial Photosynthetic Reaction Centers.


ABSTRACT: Recent studies have shown that only quinones with a 2-methoxy group can act simultaneously as the primary (QA) and secondary (QB) electron acceptors in photosynthetic reaction centers from purple bacteria such as Rb. sphaeroides. (13)C HYSCORE measurements of the 2-methoxy group in the semiquinone states, SQA and SQB, were compared with DFT calculations of the (13)C hyperfine couplings as a function of the 2-methoxy dihedral angle. X-ray structure comparisons support 2-methoxy dihedral angle assignments corresponding to a redox potential gap (?Em) between QA and QB of 175-193 mV. A model having a methyl group substituted for the 2-methoxy group exhibits no electron affinity difference. This is consistent with the failure of a 2-methyl ubiquinone analogue to function as QB in mutant reaction centers with a ?Em of ?160-195 mV. The conclusion reached is that the 2-methoxy group is the principal determinant of electron transfer from QA to QB in type II photosynthetic reaction centers with ubiquinone serving as both acceptor quinones.

SUBMITTER: de Almeida WB 

PROVIDER: S-EPMC4126703 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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The 2-Methoxy Group Orientation Regulates the Redox Potential Difference between the Primary (Q<sub>A</sub>) and Secondary (Q<sub>B</sub>) Quinones of Type II Bacterial Photosynthetic Reaction Centers.

de Almeida Wagner B WB   Taguchi Alexander T AT   Dikanov Sergei A SA   Wraight Colin A CA   O'Malley Patrick J PJ  

The journal of physical chemistry letters 20140624 15


Recent studies have shown that only quinones with a 2-methoxy group can act simultaneously as the primary (Q<sub>A</sub>) and secondary (Q<sub>B</sub>) electron acceptors in photosynthetic reaction centers from purple bacteria such as <i>Rb. sphaeroides</i>. <sup>13</sup>C HYSCORE measurements of the 2-methoxy group in the semiquinone states, SQ<sub>A</sub> and SQ<sub>B</sub>, were compared with DFT calculations of the <sup>13</sup>C hyperfine couplings as a function of the 2-methoxy dihedral an  ...[more]

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