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Manganese oxidation by modified reaction centers from Rhodobacter sphaeroides.

L Kálmán1, R LoBrutto, J P Allen

  • 1Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, USA.

Biochemistry
|September 17, 2003
PubMed
Summary

Bacterial reaction centers with higher midpoint potentials facilitate electron transfer from manganese ions. This suggests manganese oxidation may have preceded water oxidation in photosystem II evolution.

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Area of Science:

  • Biochemistry
  • Photosynthesis research
  • Electron transfer mechanisms

Background:

  • Bacterial reaction centers (BRCs) are crucial for photosynthesis.
  • Understanding electron transfer is key to deciphering energy conversion processes.

Purpose of the Study:

  • To investigate electron transfer from manganese (II) to BRCs.
  • To characterize the role of P/P(+) midpoint potential in this process.
  • To explore the evolutionary implications for photosystem II.

Main Methods:

  • Utilized BRC mutants with varying P/P(+) midpoint potentials.
  • Employed light-induced optical and EPR spectroscopy.
  • Analyzed manganese-bicarbonate interactions and kinetics.

Main Results:

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  • Electron transfer efficiency strongly correlated with P/P(+) midpoint potential.
  • Mn(2+)/Mn(3+) midpoint potential decreased with increasing pH, indicating proton involvement.
  • Second-order rate constant for electron donation was ~9 x 10(4) M(-1) s(-1).
  • Up to seven manganese ions associated with reaction centers; Ca(2+) and Na(+) inhibited binding and transfer.

Conclusions:

  • High potential BRCs can oxidize manganese, supporting evolutionary precede of water oxidation.
  • Manganese's role in early electron transfer mechanisms is highlighted.
  • Proton-coupled electron transfer is implicated in the manganese-BRC interaction.