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Biochemical characterization of the purple form of Marinobacter hydrocarbonoclasticus nitrous oxide reductase, Dell'Acqua, S., Pauleta S. R., Moura J. J., and Moura I. , Philos Trans R Soc Lond B Biol Sci, Volume 367, Issue 1593, p.1204-1212, (2012)
A Comparison between Vanadyl, Vanadate, and Decavanadate Effects in Actin Structure and Function: Combination of Several Spectroscopic Studies, Ramos, S., Moura J. J. G., and Aureliano M. , Spectroscopy: An International Journal, Volume 27, p.355-359, (2012)
Multifrequency EPR Study of Fe(3+) and Co(2+) in the Active Site of Desulforedoxin, Mathies, G., Almeida R. M., Gast P., Moura J. J., and Groenen E. J. , J Phys Chem B, Volume 116, Issue 24, p.7122-7128, (2012)
Recent advances into vanadyl, vanadate and decavanadate interactions with actin, Ramos, S., Moura J. J. G., and Aureliano M. , Metallomics, Volume 4, Issue 1, Number 1, p.16-22, (2012)
Substrate-dependent modulation of the enzymatic catalytic activity: Reduction of nitrate, chlorate and perchlorate by respiratory nitrate reductase from Marinobacter hydrocarbonoclasticus 617, Marangon, J., de Sousa Paes P. M., Moura I., Brondino C. D., Moura J. J., and González P. J. , Biochim Biophys Acta, Volume 1817, Issue 7, p.1072-1082, (2012)
Synthesis of [MoS4]2 – M (M = Cu and Cd) clusters: Potential NMR structural probes for orange protein, Maiti, B. K., Avilés T., Matzapetakis M., Moura I., Pauleta S. R., and Moura J. J. G. , Eur J Inorg Chem , Volume 2012, p.4159-4166, (2012)
New spectroscopic and electrochemical insights on a class I superoxide reductase: evidence for an intramolecular electron-transfer pathway, Folgosa, F., Cordas C. M., Santos J. A., Pereira A. S., Moura J. J., Tavares P., and Moura I. , Biochem J, Sep 15, Volume 438, Number 3, p.485-94, (2011) AbstractWebsite

SORs (superoxide reductases) are enzymes involved in bacterial resistance to reactive oxygen species, catalysing the reduction of superoxide anions to hydrogen peroxide. So far three structural classes have been identified. Class I enzymes have two iron-centre-containing domains. Most studies have focused on the catalytic iron site (centre II), yet the role of centre I is poorly understood. The possible roles of this iron site were approached by an integrated study using both classical and fast kinetic measurements, as well as direct electrochemistry. A new heterometallic form of the protein with a zinc-substituted centre I, maintaining the iron active-site centre II, was obtained, resulting in a stable derivative useful for comparison with the native all-iron from. Second-order rate constants for the electron transfer between reduced rubredoxin and the different SOR forms were determined to be 2.8 x 10 M(1) . s(1) and 1.3 x 10 M(1) . s(1) for SORFe(IIII)-Fe(II) and for SORFe(IIII)-Fe(III) forms respectively, and 3.2 x 10 M(1) . s(1) for the SORZn(II)-Fe(III) form. The results obtained seem to indicate that centre I transfers electrons from the putative physiological donor rubredoxin to the catalytic active iron site (intramolecular process). In addition, electrochemical results show that conformational changes are associated with the redox state of centre I, which may enable a faster catalytic response towards superoxide anion. The apparent rate constants calculated for the SOR-mediated electron transfer also support this observation.

Gd(III) chelates as NMR probes of protein-protein interactions. Case study: rubredoxin and cytochrome c3, Almeida, R. M., Geraldes C. F., Pauleta S. R., and Moura J. J. , Inorg Chem, Nov 7, Volume 50, Number 21, p.10600-7, (2011) AbstractWebsite

Two cyclen-derived Gd probes, [Gd-DOTAM](3+) and [Gd-DOTP](5-) (DOTAM = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide; DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonate)), were assessed as paramagnetic relaxation enhancement (PRE)-inducing probes for characterization of protein-protein interactions. Two proteins, Desulfovibrio gigas rubredoxin and Desulfovibrio gigas cytochrome c(3), were used as model partners. In a (1)H NMR titration it was shown that [Gd-DOTP](5-) binds to cytochrome c(3) near heme IV, causing pronounced PREs, characterized by line width broadenings of the heme methyl resonances at ratios as low as 0.08. A K(d) of 23 +/- 1 muM was calculated based on chemical shift perturbation of selected heme methyl resonances belonging to three different heme groups, caused by allosteric effects upon [Gd-DOTP](5-) binding to cytochrome c(3) at a molar ratio of 2. The other probe, [Gd-DOTAM](3+), caused PREs on a well-defined patch near the metal center of rubredoxin (especially the patch constituted by residues D19-G23 and W37-S45, which broaden beyond detection). This effect was partially reversed for some resonances (C6-Y11, in particular) when cytochrome c(3) was added to this system. Both probes were successful in causing reversible PREs at the partner binding site, thus showing to be good probes to identify partners' binding sites and since the interaction is reversible to structurally characterize protein complexes by better defining the complex interface.

Low-spin heme b(3) in the catalytic center of nitric oxide reductase from Pseudomonas nautica, Timoteo, C. G., Pereira A. S., Martins C. E., Naik S. G., Duarte A. G., Moura J. J., Tavares P., Huynh B. H., and Moura I. , Biochemistry, May 24, Volume 50, Number 20, p.4251-62, (2011) AbstractWebsite

Respiratory nitric oxide reductase (NOR) was purified from membrane extract of Pseudomonas (Ps.) nautica cells to homogeneity as judged by polyacrylamide gel electrophoresis. The purified protein is a heterodimer with subunits of molecular masses of 54 and 18 kDa. The gene encoding both subunits was cloned and sequenced. The amino acid sequence shows strong homology with enzymes of the cNOR class. Iron/heme determinations show that one heme c is present in the small subunit (NORC) and that approximately two heme b and one non-heme iron are associated with the large subunit (NORB), in agreement with the available data for enzymes of the cNOR class. Mossbauer characterization of the as-purified, ascorbate-reduced, and dithionite-reduced enzyme confirms the presence of three heme groups (the catalytic heme b(3) and the electron transfer heme b and heme c) and one redox-active non-heme Fe (Fe(B)). Consistent with results obtained for other cNORs, heme c and heme b in Ps. nautica cNOR were found to be low-spin while Fe(B) was found to be high-spin. Unexpectedly, as opposed to the presumed high-spin state for heme b(3), the Mossbauer data demonstrate unambiguously that heme b(3) is, in fact, low-spin in both ferric and ferrous states, suggesting that heme b(3) is six-coordinated regardless of its oxidation state. EPR spectroscopic measurements of the as-purified enzyme show resonances at the g approximately 6 and g approximately 2-3 regions very similar to those reported previously for other cNORs. The signals at g = 3.60, 2.99, 2.26, and 1.43 are attributed to the two charge-transfer low-spin ferric heme c and heme b. Previously, resonances at the g approximately 6 region were assigned to a small quantity of uncoupled high-spin Fe(III) heme b(3). This assignment is now questionable because heme b(3) is low-spin. On the basis of our spectroscopic data, we argue that the g = 6.34 signal is likely arising from a spin-spin coupled binuclear center comprising the low-spin Fe(III) heme b(3) and the high-spin Fe(B)(III). Activity assays performed under various reducing conditions indicate that heme b(3) has to be reduced for the enzyme to be active. But, from an energetic point of view, the formation of a ferrous heme-NO as an initial reaction intermediate for NO reduction is disfavored because heme [FeNO](7) is a stable product. We suspect that the presence of a sixth ligand in the Fe(II)-heme b(3) may weaken its affinity for NO and thus promotes, in the first catalytic step, binding of NO at the Fe(B)(II) site. The function of heme b(3) would then be to orient the Fe(B)-bound NO molecules for the formation of the N-N bond and to provide reducing equivalents for NO reduction.

The crystal structure of Cupriavidus necator nitrate reductase in oxidized and partially reduced states, Coelho, C., Gonzalez P. J., Moura J. G., Moura I., Trincao J., and Joao Romao M. , J Mol Biol, May 20, Volume 408, Number 5, p.932-48, (2011) AbstractWebsite

The periplasmic nitrate reductase (NapAB) from Cupriavidus necator is a heterodimeric protein that belongs to the dimethyl sulfoxide reductase family of mononuclear Mo-containing enzymes and catalyzes the reduction of nitrate to nitrite. The protein comprises a large catalytic subunit (NapA, 91 kDa) containing the molybdenum active site plus one [4Fe-4S] cluster, as well as a small subunit (NapB, 17 kDa), which is a diheme c-type cytochrome involved in electron transfer. Crystals of the oxidized form of the enzyme diffracted beyond 1.5 A at the European Synchrotron Radiation Facility. This is the highest resolution reported to date for a nitrate reductase, providing true atomic details of the protein active center, and this showed further evidence on the molybdenum coordination sphere, corroborating previous data on the related Desulfovibrio desulfuricans NapA. The molybdenum atom is bound to a total of six sulfur atoms, with no oxygen ligands or water molecules in the vicinity. In the present work, we were also able to prepare partially reduced crystals that revealed two alternate conformations of the Mo-coordinating cysteine. This crystal form was obtained by soaking dithionite into crystals grown in the presence of the ionic liquid [C(4)mim]Cl(-). In addition, UV-Vis and EPR spectroscopy studies showed that the periplasmic nitrate reductase from C. necator might work at unexpectedly high redox potentials when compared to all periplasmic nitrate reductases studied to date.

Continuous-wave EPR at 275GHz: application to high-spin Fe(3+) systems, Mathies, G., Blok H., Disselhorst J. A., Gast P., van der Meer H., Miedema D. M., Almeida R. M., Moura J. J., Hagen W. R., and Groenen E. J. , J Magn Reson, May, Volume 210, Number 1, p.126-32, (2011) AbstractWebsite

The 275GHz electron-paramagnetic-resonance spectrometer we reported on in 2004 has been equipped with a new probe head, which contains a cavity especially designed for operation in continuous-wave mode. The sensitivity and signal stability that is achieved with this new probe head is illustrated with 275GHz continuous-wave spectra of a 1mM frozen solution of the complex Fe(III)-ethylenediamine tetra-acetic acid and of 10mM frozen solutions of the protein rubredoxin, which contains Fe(3+) in its active site, from three different organisms. The high quality of the spectra of the rubredoxins allows the determination of the zero-field-splitting parameters with an accuracy of 0.5GHz. The success of our approach results partially from the enhanced absolute sensitivity, which can be reached using a single-mode cavity. At least as important is the signal stability that we were able to achieve with the new probe head.

Nitrite reduction by xanthine oxidase family enzymes: a new class of nitrite reductases, Maia, L. B., and Moura J. J. , J Biol Inorg Chem, Mar, Volume 16, Number 3, p.443-60, (2011) AbstractWebsite

Mammalian xanthine oxidase (XO) and Desulfovibrio gigas aldehyde oxidoreductase (AOR) are members of the XO family of mononuclear molybdoenzymes that catalyse the oxidative hydroxylation of a wide range of aldehydes and heterocyclic compounds. Much less known is the XO ability to catalyse the nitrite reduction to nitric oxide radical (NO). To assess the competence of other XO family enzymes to catalyse the nitrite reduction and to shed some light onto the molecular mechanism of this reaction, we characterised the anaerobic XO- and AOR-catalysed nitrite reduction. The identification of NO as the reaction product was done with a NO-selective electrode and by electron paramagnetic resonance (EPR) spectroscopy. The steady-state kinetic characterisation corroborated the XO-catalysed nitrite reduction and demonstrated, for the first time, that the prokaryotic AOR does catalyse the nitrite reduction to NO, in the presence of any electron donor to the enzyme, substrate (aldehyde) or not (dithionite). Nitrite binding and reduction was shown by EPR spectroscopy to occur on a reduced molybdenum centre. A molecular mechanism of AOR- and XO-catalysed nitrite reduction is discussed, in which the higher oxidation states of molybdenum seem to be involved in oxygen-atom insertion, whereas the lower oxidation states would favour oxygen-atom abstraction. Our results define a new catalytic performance for AOR-the nitrite reduction-and propose a new class of molybdenum-containing nitrite reductases.

Effects of molybdate and tungstate on expression levels and biochemical characteristics of formate dehydrogenases produced by Desulfovibrio alaskensis NCIMB 13491, Mota, C. S., Valette O., Gonzalez P. J., Brondino C. D., Moura J. J., Moura I., Dolla A., and Rivas M. G. , J Bacteriol, Jun, Volume 193, Number 12, p.2917-23, (2011) AbstractWebsite

Formate dehydrogenases (FDHs) are enzymes that catalyze the formate oxidation to carbon dioxide and that contain either Mo or W in a mononuclear form in the active site. In the present work, the influence of Mo and W salts on the production of FDH by Desulfovibrio alaskensis NCIMB 13491 was studied. Two different FDHs, one containing W (W-FDH) and a second incorporating either Mo or W (Mo/W-FDH), were purified. Both enzymes were isolated from cells grown in a medium supplemented with 1 muM molybdate, whereas only the W-FDH was purified from cells cultured in medium supplemented with 10 muM tungstate. We demonstrated that the genes encoding the Mo/W-FDH are strongly downregulated by W and slightly upregulated by Mo. Metal effects on the expression level of the genes encoding the W-FDH were less significant. Furthermore, the expression levels of the genes encoding proteins involved in molybdate and tungstate transport are downregulated under the experimental conditions evaluated in this work. The molecular and biochemical properties of these enzymes and the selective incorporation of either Mo or W are discussed.

The Anaerobe-Specific Orange Protein Complex of Desulfovibrio vulgaris Hildenborough Is Encoded by Two Divergent Operons Coregulated by sigma(54) and a Cognate Transcriptional Regulator, Fievet, Anouchka, My Laetitia, Cascales Eric, Ansaldi Mireille, Pauleta Sofia R., Moura Isabel, Dermoun Zorah, Bernard Christophe S., Dolla Alain, and Aubert Corinne , Journal of Bacteriology, Jul, Volume 193, Number 13, p.3207-3219, (2011) AbstractWebsite

Analysis of sequenced bacterial genomes revealed that the genomes encode more than 30% hypothetical and conserved hypothetical proteins of unknown function. Among proteins of unknown function that are conserved in anaerobes, some might be determinants of the anaerobic way of life. This study focuses on two divergent clusters specifically found in anaerobic microorganisms and mainly composed of genes encoding conserved hypothetical proteins. We show that the two gene clusters DVU2103-DVU2104-DVU2105 (orp2) and DVU2107-DVU2108-DVU2109 (orp1) form two divergent operons transcribed by the sigma(54)-RNA polymerase. We further demonstrate that the sigma(54)-dependent transcriptional regulator DVU2106, located between orp1 and orp2, collaborates with sigma(54)-RNA polymerase to orchestrate the simultaneous expression of the divergent orp operons. DVU2106, whose structural gene is transcribed by the sigma(70)-RNA polymerase, negatively retrocontrols its own expression. By using an endogenous pulldown strategy, we identify a physiological complex composed of DVU2103, DVU2104, DVU2105, DVU2108, and DVU2109. Interestingly, inactivation of DVU2106, which is required for orp operon transcription, induces morphological defects that are likely linked to the absence of the ORP complex. A putative role of the ORP proteins in positioning the septum during cell division is discussed.

Crystal structure of the zinc-, cobalt-, and iron-containing adenylate kinase from Desulfovibrio gigas: a novel metal-containing adenylate kinase from Gram-negative bacteria, Mukhopadhyay, A., Kladova A. V., Bursakov S. A., Gavel O. Y., Calvete J. J., Shnyrov V. L., Moura I., Moura J. J., Romao M. J., and Trincao J. , J Biol Inorg Chem, Jan, Volume 16, Number 1, p.51-61, (2011) AbstractWebsite

Adenylate kinases (AK) from Gram-negative bacteria are generally devoid of metal ions in their LID domain. However, three metal ions, zinc, cobalt, and iron, have been found in AK from Gram-negative bacteria. Crystal structures of substrate-free AK from Desulfovibrio gigas with three different metal ions (Zn(2+), Zn-AK; Co(2+), Co-AK; and Fe(2+), Fe-AK) bound in its LID domain have been determined by X-ray crystallography to resolutions 1.8, 2.0, and 3.0 A, respectively. The zinc and iron forms of the enzyme were crystallized in space group I222, whereas the cobalt-form crystals were C2. The presence of the metals was confirmed by calculation of anomalous difference maps and by X-ray fluorescence scans. The work presented here is the first report of a structure of a metal-containing AK from a Gram-negative bacterium. The native enzyme was crystallized, and only zinc was detected in the LID domain. Co-AK and Fe-AK were obtained by overexpressing the protein in Escherichia coli. Zn-AK and Fe-AK crystallized as monomers in the asymmetric unit, whereas Co-AK crystallized as a dimer. Nevertheless, all three crystal structures are very similar to each other, with the same LID domain topology, the only change being the presence of the different metal atoms. In the absence of any substrate, the LID domain of all holoforms of AK was present in a fully open conformational state. Normal mode analysis was performed to predict fluctuations of the LID domain along the catalytic pathway.

Artefacts induced on c-type haem proteins by electrode surfaces, Paes de Sousa, P. M., Pauleta S. R., Simoes Goncalves M. L., Pettigrew G. W., Moura I., Moura J. J., and Correia dos Santos M. M. , J Biol Inorg Chem, Feb, Volume 16, Number 2, p.209-15, (2011) AbstractWebsite

In this work it is demonstrated that the characterization of c-type haem containing proteins by electrochemical techniques needs to be cautiously performed when using pyrolytic graphite electrodes. An altered form of the cytochromes, which has a redox potential 300 mV lower than that of the native state and displays peroxidatic activity, can be induced by interaction with the pyrolytic graphite electrode. Proper control experiments need to be performed, as altered conformations of the enzymes containing c-type haems can show activity towards the enzyme substrate. The work was focused on the study of the activation mechanism and catalytic activity of cytochrome c peroxidase from Paracoccus pantotrophus. The results could only be interpreted with the assignment of the observed non-turnover and catalytic signals to a non-native conformation state of the electron-transferring haem. The same phenomenon was detected for Met-His monohaem cytochromes (mitochondrial cytochrome c and Desulfovibrio vulgaris cytochrome c-553), as well as for the bis-His multihaem cytochrome c(3) from Desulfovibrio gigas, showing that this effect is independent of the axial coordination of the c-type haem protein. Thus, the interpretation of electrochemical signals of c-type (multi)haem proteins at pyrolytic graphite electrodes must be carefully performed, to avoid misassignment of the signals and incorrect interpretation of catalytic intermediates.

The tetranuclear copper active site of nitrous oxide reductase: the CuZ center, Dell'Acqua, S., Pauleta S. R., Moura I., and Moura J. J. , J Biol Inorg Chem, Feb, Volume 16, Number 2, p.183-94, (2011) AbstractWebsite

This review focuses on the novel CuZ center of nitrous oxide reductase, an important enzyme owing to the environmental significance of the reaction it catalyzes, reduction of nitrous oxide, and the unusual nature of its catalytic center, named CuZ. The structure of the CuZ center, the unique tetranuclear copper center found in this enzyme, opened a novel area of research in metallobiochemistry. In the last decade, there has been progress in defining the structure of the CuZ center, characterizing the mechanism of nitrous oxide reduction, and identifying intermediates of this reaction. In addition, the determination of the structure of the CuZ center allowed a structural interpretation of the spectroscopic data, which was supported by theoretical calculations. The current knowledge of the structure, function, and spectroscopic characterization of the CuZ center is described here. We would like to stress that although many questions have been answered, the CuZ center remains a scientific challenge, with many hypotheses still being formed.

Actin as a potential target for decavanadate, Ramos, S., Moura J. J., and Aureliano M. , J Inorg Biochem, Dec, Volume 104, Number 12, p.1234-9, (2011) AbstractWebsite

ATP prevents G-actin cysteine oxidation and vanadyl formation specifically induced by decavanadate, suggesting that the oxometalate-protein interaction is affected by the nucleotide. The ATP exchange rate is increased by 2-fold due to the presence of decavanadate when compared with control actin (3.1x10(-3) s(-1)), and an apparent dissociation constant (k(dapp)) of 227.4+/-25.7 muM and 112.3+/-8.7 muM was obtained in absence or presence of 20 muM V(10), respectively. Moreover, concentrations as low as 50 muM of decameric vanadate species (V(10)) increases the relative G-actin intrinsic fluorescence intensity by approximately 80% whereas for a 10-fold concentration of monomeric vanadate (V(1)) no effects were observed. Upon decavanadate titration, it was observed a linear increase in G-actin hydrophobic surface (2.6-fold), while no changes were detected for V(1) (0-200 muM). Taken together, three major ideas arise: i) ATP prevents decavanadate-induced G-actin cysteine oxidation and vanadate reduction; ii) decavanadate promotes actin conformational changes resulting on its inactivation, iii) decavanadate has an effect on actin ATP binding site. Once it is demonstrated that actin is a new potential target for decavanadate, being the ATP binding site a suitable site for decavanadate binding, it is proposed that some of the biological effects of vanadate can be, at least in part, explained by decavanadate interactions with actin.

The electron transfer complex between nitrous oxide reductase and its electron donors, Dell'Acqua, S., Moura I., Moura J. J., and Pauleta S. R. , J Biol Inorg Chem, Dec, Volume 16, Number 8, p.1241-54, (2011) AbstractWebsite

Identifying redox partners and the interaction surfaces is crucial for fully understanding electron flow in a respiratory chain. In this study, we focused on the interaction of nitrous oxide reductase (N(2)OR), which catalyzes the final step in bacterial denitrification, with its physiological electron donor, either a c-type cytochrome or a type 1 copper protein. The comparison between the interaction of N(2)OR from three different microorganisms, Pseudomonas nautica, Paracoccus denitrificans, and Achromobacter cycloclastes, with their physiological electron donors was performed through the analysis of the primary sequence alignment, electrostatic surface, and molecular docking simulations, using the bimolecular complex generation with global evaluation and ranking algorithm. The docking results were analyzed taking into account the experimental data, since the interaction is suggested to have either a hydrophobic nature, in the case of P. nautica N(2)OR, or an electrostatic nature, in the case of P. denitrificans N(2)OR and A. cycloclastes N(2)OR. A set of well-conserved residues on the N(2)OR surface were identified as being part of the electron transfer pathway from the redox partner to N(2)OR (Ala495, Asp519, Val524, His566 and Leu568 numbered according to the P. nautica N(2)OR sequence). Moreover, we built a model for Wolinella succinogenes N(2)OR, an enzyme that has an additional c-type-heme-containing domain. The structures of the N(2)OR domain and the c-type-heme-containing domain were modeled and the full-length structure was obtained by molecular docking simulation of these two domains. The orientation of the c-type-heme-containing domain relative to the N(2)OR domain is similar to that found in the other electron transfer complexes.

The mechanism of formate oxidation by metal-dependent formate dehydrogenases, Mota, C. S., Rivas M. G., Brondino C. D., Moura I., Moura J. J., Gonzalez P. J., and Cerqueira N. M. , J Biol Inorg Chem, Dec, Volume 16, Number 8, p.1255-68, (2011) AbstractWebsite

Metal-dependent formate dehydrogenases (Fdh) from prokaryotic organisms are members of the dimethyl sulfoxide reductase family of mononuclear molybdenum-containing and tungsten-containing enzymes. Fdhs catalyze the oxidation of the formate anion to carbon dioxide in a redox reaction that involves the transfer of two electrons from the substrate to the active site. The active site in the oxidized state comprises a hexacoordinated molybdenum or tungsten ion in a distorted trigonal prismatic geometry. Using this structural model, we calculated the catalytic mechanism of Fdh through density functional theory tools. The simulated mechanism was correlated with the experimental kinetic properties of three different Fdhs isolated from three different Desulfovibrio species. Our studies indicate that the C-H bond break is an event involved in the rate-limiting step of the catalytic cycle. The role in catalysis of conserved amino acid residues involved in metal coordination and near the metal active site is discussed on the basis of experimental and theoretical results.

Analysis of the activation mechanism of Pseudomonas stutzeri cytochrome c peroxidase through an electron transfer chain, Paes de Sousa, P. M., Rodrigues D., Timoteo C. G., Simoes Goncalves M. L., Pettigrew G. W., Moura I., Moura J. J., and Correia dos Santos M. M. , J Biol Inorg Chem, Aug, Volume 16, Number 6, p.881-8, (2011) AbstractWebsite

The activation mechanism of Pseudomonas stutzeri cytochrome c peroxidase (CCP) was probed through the mediated electrochemical catalysis by its physiological electron donor, P. stutzeri cytochrome c-551. A comparative study was carried out, by performing assays with the enzyme in the resting oxidized state as well as in the mixed-valence activated form, using cyclic voltammetry and a pyrolytic graphite membrane electrode. In the presence of both the enzyme and hydrogen peroxide, the peak-like signal of cytochrome c-551 is converted into a sigmoidal wave form characteristic of an E(r)C'(i) catalytic mechanism. An intermolecular electron transfer rate constant of (4 +/- 1) x 10(5) M(-1) s(-1) was estimated for both forms of the enzyme, as well as a similar Michaelis-Menten constant. These results show that neither the intermolecular electron transfer nor the catalytic activity is kinetically controlled by the activation mechanism of CCP in the case of the P. stutzeri enzyme. Direct enzyme catalysis using protein film voltammetry was unsuccessful for the analysis of the activation mechanism, since P. stutzeri CCP undergoes an undesirable interaction with the pyrolytic graphite surface. This interaction, previously reported for the Paracoccus pantotrophus CCP, induces the formation of a non-native conformation state of the electron-transferring haem, which has a redox potential 200 mV lower than that of the native state and maintains peroxidatic activity.

Structural redox control in a 7Fe ferredoxin isolated from Desulfovibrio alaskensis, Grazina, R., de Sousa P. M., Brondino C. D., Carepo M. S., Moura I., and Moura J. J. , Bioelectrochemistry, Aug, Volume 82, Number 1, p.22-8, (2011) AbstractWebsite

The redox behaviour of a ferredoxin (Fd) from Desulfovibrio alaskensis was characterized by electrochemistry. The protein was isolated and purified, and showed to be a tetramer containing one [3Fe-4S] and one [4Fe-4S] centre. This ferredoxin has high homology with FdI from Desulfovibrio vulgaris Miyazaki and Hildenborough and FdIII from Desulfovibrio africanus. From differential pulse voltammetry the following signals were identified: [3Fe-4S](+1/0) (E(0')=-158+/-5mV); [4Fe-4S](+2/+1) (E(0')=-474+/-5mV) and [3Fe-4S](0/-2) (E(0')=-660+/-5mV). The effect of pH on these signals showed that the reduced [3Fe-4S](0) cluster has a pK'(red)(')=5.1+/-0.1, the [4Fe-4S](+2/+1) centre is pH independent, and the [3Fe-4S](0/-2) reduction is accompanied by the binding of two protons. The ability of the [3Fe-4S](0) cluster to be converted into a new [4Fe-4S] cluster was proven. The redox potential of the original [4Fe-4S] centre showed to be dependent on the formation of the new [4Fe-4S] centre, which results in a positive shift (ca. 70mV) of the redox potential of the original centre. Being most [Fe-S] proteins involved in electron transport processes, the electrochemical characterization of their clusters is essential to understand their biological function. Complementary EPR studies were performed.

Cooperative use of cytochrome cd1 nitrite reductase and its redox partner cytochrome c552 to Improve the selectivity of nitrite biosensing, A.S., Serra, S. Jorge, C. Silveira, J.J.G. Moura, E. Jubete, E. Ochoteco, and G. Almeida M. , Anal Chim Acta, Volume 693, p.41-46, (2011)
Implications of oxidovanadium (IV) binding to actin, Ramos, S., Almeida R. M., Moura J. J., and Aureliano M. , Eur J Inorg Chem, Volume 105, Issue 6, p.777, (2011)