Iron as a bound secondary electron donor in modified bacterial reaction centers

L. Kálmán, R. LoBrutto, J. C. Williams, James Paul Allen

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The binding and oxidation of ferrous iron were studied in wild-type reaction centers and in mutants that have been modified to be both highly oxidizing and able to bind manganese [Thielges et al. (2005) Biochemistry 44, 7389-7394]. After illumination of wild-type reaction centers, steady-state optical spectroscopy showed that the oxidized bacteriochlorophyll dimer, P +, could oxidize iron but only as a second-order reaction at iron concentrations above 100 μM. In the modified reaction centers, P+ was reduced by iron in the presence of sodium bicarbonate with dissociation constants of ∼1 μM for two mutants with different metal-binding sites. Transient optical spectroscopy showed that P+ was rapidly reduced with first-order rates of 170 and 275 s-1 for the two mutants. The dependence of the amplitude of this rate on the iron concentration yielded a dissociation constant of ∼1 μM for both mutants, in agreement with the steady-state determination. The oxidation of bound iron by P+ was confirmed by the observation of a light-induced EPR signal centered at g values of 2.2 and 4.3 and attributed to high-spin Fe3+. Bicarbonate was required at pH 7 for low dissociation constants for both iron and manganese binding. The similarity between iron and manganese binding in these mutants provides insight into general properties of metal-binding sites in proteins.

Original languageEnglish
Pages (from-to)13869-13874
Number of pages6
JournalBiochemistry
Volume45
Issue number46
DOIs
Publication statusPublished - Nov 21 2006

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Iron
Electrons
Manganese
Spectrum Analysis
Metals
Binding Sites
Bacteriochlorophylls
Oxidation
Biochemistry
Sodium Bicarbonate
Bicarbonates
Lighting
Dimers
Paramagnetic resonance
Observation
Light
Proteins

ASJC Scopus subject areas

  • Biochemistry

Cite this

Iron as a bound secondary electron donor in modified bacterial reaction centers. / Kálmán, L.; LoBrutto, R.; Williams, J. C.; Allen, James Paul.

In: Biochemistry, Vol. 45, No. 46, 21.11.2006, p. 13869-13874.

Research output: Contribution to journalArticle

Kálmán, L. ; LoBrutto, R. ; Williams, J. C. ; Allen, James Paul. / Iron as a bound secondary electron donor in modified bacterial reaction centers. In: Biochemistry. 2006 ; Vol. 45, No. 46. pp. 13869-13874.
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