Electron Transfer in the Reaction Center From Rhodopseudomonas Viridis (Photosynthesis, Bioenergetics, Bacteria)

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).

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biophysics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Shopes, Robert James

• Biophysics, General

Identifier

(UMI)AAI8701617

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70715