On rate limitations of electron transfer in the photosynthetic cytochrome b6f complex.

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TitleOn rate limitations of electron transfer in the photosynthetic cytochrome b6f complex.
Publication TypeJournal Article
Year of Publication2012
AuthorsS Hasan, S, Cramer, WA
JournalPhys Chem Chem Phys
Volume14
Issue40
Pagination13853-60
Date Published2012 Oct 28
ISSN1463-9084
KeywordsAmino Acid Sequence, Chlamydomonas reinhardtii, Crystallography, X-Ray, Cyanobacteria, Cytochrome b6f Complex, Electron Transport, Electrons, Kinetics, Models, Molecular, Molecular Sequence Data, Oxidation-Reduction, Photosynthesis, Sequence Alignment
Abstract

Considering information in the crystal structures of the cytochrome b(6)f complex relevant to the rate-limiting step in oxygenic photosynthesis, it is enigmatic that electron transport in the complex is not limited by the large distance, approximately 26 Å, between the iron-sulfur cluster (ISP) and its electron acceptor, cytochrome f. This enigma has been explained for the respiratory bc(1) complex by a crystal structure with a greatly shortened cluster-heme c(1) distance, leading to a concept of ISP dynamics in which the ISP soluble domain undergoes a translation-rotation conformation change and oscillates between positions relatively close to the cyt c(1) heme and a membrane-proximal position close to the ubiquinol electron-proton donor. Comparison of cytochrome b(6)f structures shows a variation in cytochrome f heme position that suggests the possibility of flexibility and motion of the extended cytochrome f structure that could entail a transient decrease in cluster-heme f distance. The dependence of cyt f turnover on lumen viscosity is consistent with a role of ISP - cyt f dynamics in determination of the rate-limiting step under conditions of low light intensity. Under conditions of low light intensity and proton electrochemical gradient present, for example, under a leaf canopy, it is proposed that a rate limitation of electron transport in the b(6)f complex may also arise from steric constraints in the entry/exit portal for passage of the plastoquinol and -quinone to/from its oxidation site proximal to the iron-sulfur cluster.

DOI10.1039/c2cp41386h
Alternate JournalPhys Chem Chem Phys
PubMed ID22890107
PubMed Central IDPMC3505453
Grant ListR01 GM038323 / GM / NIGMS NIH HHS / United States
R56 GM038323 / GM / NIGMS NIH HHS / United States
GM-038323 / GM / NIGMS NIH HHS / United States