Moessbauer study of D. gigas ferredoxin II and spin-coupling model for Fe3S4 cluster with valence delocalization,
Papaefthymiou, V., Girerd J. J., Moura I., Moura J. J. G., and Muenck E.
, Journal of the American Chemical Society, 1987/07/01, Volume 109, Number 15, p.4703-4710, (1987)
Abstractn/a
Marinobacter hydrocarbonoclasticus is an aerobic denitrifier,
Pauleta, S. R., Ramos S., Pietsch M., Carreira C., Dell'Acqua S., and Moura I.
, EuroBIC 11, Granada, p.49-53, (2013)
Mossbauer characterization of the iron-sulfur clusters in Desulfovibrio vulgaris hydrogenase,
Pereira, A. S., Tavares P., Moura I., Moura J. J., and Huynh B. H.
, J Am Chem Soc, Mar 28, Volume 123, Number 12, p.2771-82, (2001)
AbstractThe periplasmic hydrogenase of Desulfovibrio vulgaris (Hildenbourough) is an all Fe-containing hydrogenase. It contains two ferredoxin type [4Fe-4S] clusters, termed the F clusters, and a catalytic H cluster. Recent X-ray crystallographic studies on two Fe hydrogenases revealed that the H cluster is composed of two sub-clusters, a [4Fe-4S] cluster ([4Fe-4S](H)) and a binuclear Fe cluster ([2Fe](H)), bridged by a cysteine sulfur. The aerobically purified D. vulgaris hydrogenase is stable in air. It is inactive and requires reductive activation. Upon reduction, the enzyme becomes sensitive to O(2), indicating that the reductive activation process is irreversible. Previous EPR investigations showed that upon reoxidation (under argon) the H cluster exhibits a rhombic EPR signal that is not seen in the as-purified enzyme, suggesting a conformational change in association with the reductive activation. For the purpose of gaining more information on the electronic properties of this unique H cluster and to understand further the reductive activation process, variable-temperature and variable-field Mossbauer spectroscopy has been used to characterize the Fe-S clusters in D. vulgaris hydrogenase poised at different redox states generated during a reductive titration, and in the CO-reacted enzyme. The data were successfully decomposed into spectral components corresponding to the F and H clusters, and characteristic parameters describing the electronic and magnetic properties of the F and H clusters were obtained. Consistent with the X-ray crystallographic results, the spectra of the H cluster can be understood as originating from an exchange coupled [4Fe-4S]-[2Fe] system. In particular, detailed analysis of the data reveals that the reductive activation begins with reduction of the [4Fe-4S](H) cluster from the 2+ to the 1+ state, followed by transfer of the reducing equivalent from the [4Fe-4S](H) subcluster to the binuclear [2Fe](H) subcluster. The results also reveal that binding of exogenous CO to the H cluster affects significantly the exchange coupling between the [4Fe-4S](H) and the [2Fe](H) subclusters. Implication of such a CO binding effect is discussed.
Mossbauer characterization of Paracoccus denitrificans cytochrome c peroxidase. Further evidence for redox and calcium binding-induced heme-heme interaction,
Prazeres, S., Moura J. J., Moura I., Gilmour R., Goodhew C. F., Pettigrew G. W., Ravi N., and Huynh B. H.
, J Biol Chem, Oct 13, Volume 270, Number 41, p.24264-9, (1995)
AbstractMossbauer and electron paramagnetic resonance (EPR) spectroscopies were used to characterize the diheme cytochrome c peroxidase from Paracoccus denitrificans (L.M.D. 52.44). The spectra of the oxidized enzyme show two distinct spectral components characteristic of low spin ferric hemes (S = 1/2), revealing different heme environments for the two heme groups. The Paracoccus peroxidase can be non-physiologically reduced by ascorbate. Mossbauer investigation of the ascorbate-reduced peroxidase shows that only one heme (the high potential heme) is reduced and that the reduced heme is diamagnetic (S = 0). The other heme (the low potential heme) remains oxidized, indicating that the enzyme is in a mixed valence, half-reduced state. The EPR spectrum of the half-reduced peroxidase, however, shows two low spin ferric species with gmax = 2.89 (species I) and gmax = 2.78 (species II). This EPR observation, together with the Mossbauer result, suggests that both species are arising from the low potential heme. More interestingly, the spectroscopic properties of these two species are distinct from that of the low potential heme in the oxidized enzyme, providing evidence for heme-heme interaction induced by the reduction of the high potential heme. Addition of calcium ions to the half-reduced enzyme converts species II to species I. Since calcium has been found to promote peroxidase activity, species I may represent the active form of the peroxidatic heme.