ISBN: 978-83-60043-10-3 - eurobic9

P68. [3Fe-4S] Cluster Reduced States
Electrochemical and EPR Studies
R. Grazina, P. P. Sousa, M. Carepo, I. Moura and J. J. G. Moura
Eurobic9, 2-6 September, 2008, Wrocław, Poland
REQUIMTE, Departamento de Química, Centro de Química Fina e Biotecnologia, Faculdade de Ciências e
Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
e-mail: raquel.grazina@dq.fct.unl.pt
Ferredoxins are simple iron-sulphur proteins that contain prosthetic groups composed of iron and sulphur atoms
and they play a functional role in electron transfer processes relevant for sulphate-reducing bacteria (SRB)
metabolism. In particular, Desulfovibrio gigas ferredoxin II (DgFdII) is a small tetrameric protein of 58 amino
acids which contains a single [3Fe-4S] cluster and a redox active internal disulfide bridge [1, 2]. Electrochemical
tools can provide important information for the understanding of the redox and mechanistic/structural role of Fe-
S clusters and to the interconvertion process occurring between 3 Fe and 4 Fe clusters, as well as to the effect of
the addition of an extra metal to form heterometal clusters of the type [M3Fe-4S] ) [3]. From direct
electrochemistry (cyclic voltammetry and differential pulse voltammetry) the DgFdII presents two distinct
electrochemical signals correspondent to the following transitions: [3Fe-4S] +1/0 and [3Fe-4S] 0/-2 . Concerning the
electronic properties of the [3Fe-4S] cluster these have been also explored by EPR spectroscopy and besides the
two sates already assigned in the literature for the oxidized state [3Fe-4S] +1 (S = 1/2 and g = 2.02) [4] and for the
reduced state [3Fe-4S] 0 (S = 2 and EPR transition around g = 12) [5, 6], a new reduced state was also achieved
using titanium(III) citrate, as reductant, and EPR signals at very low magnetic fields were observed. This further
reduced state is also being attempted to be generated by bulk electrochemical methods.
Acknowledgments: We thank FCT-MCTES for financial support.
References:
[1] Moura et al., Methods in Enzymology, Vol. 243, 166-188 (1994), Peck, HD and LeGall, J, Ed., AP.
[2] Moura et al., in Methods in Enzymology, J.H.D. Peck and J. LeGall Editors (1994).
[3] Moreno et al., J. Inorg. Biochem., 53, 219 (1994).
[4] Huynh et al., J. Biol. Chem., 255, 3243 (1980).
[5] Papaefthymiou et al., J. Am. Chem. Soc., 109, 4703 (1987).
[6] Bush et al., Biochem. J., 323, 95 (1997).
_____________________________________________________________________
187