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Circular-dichroism and magnetic circular-dichroism of azotobacter-vinelandii ferredoxin-i

Academic Article
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Overview

authors

  • Stephens, P. J.
  • Jensen, G. M.
  • Devlin, F. J.
  • Morgan, T. V.
  • Stout, C. David
  • Martin, A. E.
  • Burgess, B. K.

publication date

  • April 1991

journal

  • Biochemistry  Journal

abstract

  • Room temperature circular dichroism (CD) and low temperature magnetic circular dichroism (MCD) spectra of air-oxidized and dithionite-reduced Azotobacter vinelandii ferredoxin I (FdI), a [( 4Fe-4S]2+/1+, [3Fe-4S]1+/0) protein, are reported. Unlike the CD of oxidized FdI, the CD of dithionite-reduced FdI exhibits significant pH dependence, consistent with protonation-deprotonation at or near the cluster reduced: the [3Fe-4S] cluster. The MCD of reduced FdI, which originates in the paramagnetic reduced [3Fe-4S]0 cluster, is also pH-dependent. Detailed studies of the field dependence and temperature dependence of the MCD of oxidized and reduced FdI, in the latter case at pH 6.0 and 8.3, are reported. The low-field temperature dependence of the MCD of oxidized FdI, which originates in the paramagnetic oxidized [3Fe-4S]1+ cluster, establishes the absence of a significant population of excited electronic states of this cluster up to 60 K. The low-field temperature dependence of the MCD of reduced FdI establishes that the ground-state manifold of the reduced [3Fe-4S]0 cluster possesses S greater than or equal to 2 at both pH 6.0 and 8.3. Analysis, assuming S = 2 and an axial zero-field splitting Hamiltonian, leads to D = -2.0 and -3.5 cm-1 at pH 6.0 and 8.3, respectively. The site of the (de)protonation affecting the spectroscopic properties of the [3Fe-4S] cluster remains unknown.

subject areas

  • Azotobacter
  • Circular Dichroism
  • Ferredoxins
  • Mathematics
  • Protein Conformation
  • Spectrophotometry
  • Thermodynamics
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Identity

International Standard Serial Number (ISSN)

  • 0006-2960

Digital Object Identifier (DOI)

  • 10.1021/bi00227a007

PubMed ID

  • 2009261
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Additional Document Info

start page

  • 3200

end page

  • 3209

volume

  • 30

issue

  • 13

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