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Protein Environments and Electron Transfer Processes Probed with High-Frequency ENDOR

  • Oleg G. Poluektov
  • Lisa M. Utschig
Part of the Advances in Photosynthesis and Respiration book series (AIPH, volume 28)

Summary

Natural photosynthetic conversion of solar energy to chemical energy is a unique phenomenon which sustains all life on Earth. The key step of photosynthetic energy conversion involves rapid, photoinduced sequential electron transfers (ET) resulting in efficient charge separation across a biological membrane. Fundamental to fully understanding these ET events is discerning the involvement of heterogeneous polypeptide environments surrounding the redox cofactor sites. High-resolution X-ray crystal structures of reaction center (RC) proteins reveal the structure of cofactors and surrounding protein environments; however, static crystallographic protein structures do not readily yield details of how native dynamic solution protein structures fine-tune ET processes and coupled reactions, such as proton transfer. Thus, novel approaches complementary to crystallography are required to experimentally correlate structural, electrostatic, and dynamic features of localized protein environments with inherent ET reactions. In this chapter we discuss one of the advanced experimental techniques being developed to tackle this problem. Using recent examples from our laboratory, we demonstrate the potential of high-frequency (HF), time-resolved (TR) electron-nuclear double resonance (ENDOR) spectroscopy to reveal unique information about structure/function relationships in photosynthetic ET. First, we discuss light-induced protein conformational states of P+Q B trapped in purple photosynthetic bacterial RCs at low temperature and matrix ENDOR techniques for examining the local protein environment surrounding Q B for these states. Second, we describe the HF TR ENDOR study of the spin-correlated radical pair P+Q A . These experiments permit us to directly probe light-induced reorganization of the protein in response to the rapid formation of the charge-separated state. General principles obtained from the novel application of these methodological approaches to native biological systems will help in the development of biomimetic solar energy conversion assemblies.

Keywords

Electron Paramagnetic Resonance Electron Paramagnetic Resonance Spectrum Electron Paramagnetic Resonance Signal Rhodobacter Sphaeroides Photosynthetic Reaction Center 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Abbreviations

A1

phylloquinone acceptor

Blc.

Blastochloris

DAF

delay after flash

ENDOR

electron-nuclear double resonance

EPR

electron paramagnetic resonance

ESE

electron spin echo

ET

electron transfer

HF

high-frequency

HFI

hyperfine interactions

MW

microwave

P

primary donor

P700

primary chlorophyll electron donor

Q

quinone

Rba.

Rhodobacter

RC

reaction center

RF

radiofrequency

SCRP

spin-correlated radical pair

TR

time-resolved

UQ

ubiquinone

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© Springer Science + Business Media B.V 2009

Authors and Affiliations

  1. 1.Chemistry DivisionArgonne National LaboratoryArgonneUSA

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