Electron Transfer in the Reaction Center From Rhodopseudomonas Viridis (Photosynthesis, Bioenergetics, Bacteria)
Shopes, Robert James
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https://hdl.handle.net/2142/70715
Description
Title
Electron Transfer in the Reaction Center From Rhodopseudomonas Viridis (Photosynthesis, Bioenergetics, Bacteria)
Author(s)
Shopes, Robert James
Issue Date
1986
Department of Study
Physiology and Biophysics
Discipline
Biophysics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biophysics, General
Abstract
The dissertation research was the characterization of photoinduced electron transfer in the reaction center protein involved in bacterial photosynthesis of the species Rhodopseudomonas viridis. The quinone acceptor complex behaves as a two electron gate, to shuttle electrons and protons through the reaction center, as in other photosynthetic bacterial reaction centers and in Photosystem II of plants. The primary quinone, Q(,A), was identified as menaquinone and the secondary quinone, Q(,B), as a ubiquinone. The forward electron transfer equilibrium, from Q(,A) to Q(,B), was found to be driven by a large enthalpy decrease which compensated a decrease in entropy. This electron transfer was inhibited by some herbicides which act at Photosystem II. Two mutant strains, tolerant to the herbicide Terbutryn, were characterized and found to have lowered binding affinity for the substrate ubiquinone as well as the inhibitor, suggesting that the inhibitors (e.g. s-triazines) mimic the quinone rather than the semiquinone. The kinetics of charge recombination between the photooxidized primary donor, P('+), and the photoreduced quinone acceptors were measured. The temperature dependence of the P('+) Q(,A)('-) recovery kinetic revealed a novel indirect route as well as the more typical electron tunneling pathway, as a mechanism for this charge recombination. A charge recombination between the bound photooxidized secondary donor, cytochrome c(,558)('+), and Q(,A)('-) also occurs. A detailed study of the temperature and pH dependencies of the kinetics of this reaction and of the redox midpoint potentials for the components, substantiated a mechanism for the charge recombination of the state cytochrome c(,558)('+) Q(,A)('-) as an equilibration of the positive hole between cytochrome c(,558) and P and return of the electron via the P('+) Q(,A)('-) state. The oxidation rates of cytochrome c(,558) and cytochrome c(,533) by P('+) were measured. An electron equilibration step was discovered between the initially oxidized cytochrome c(,558) and the other bound cytochrome c(,558).
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