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The effect of pH on Marinobacter hydrocarbonoclasticus denitrification pathway and nitrous oxide reductase, Carreira, C., Nunes R. F., Mestre O., Moura I., and Pauleta S. R. , J Biol Inorg Chem, Volume 25, p.927, (2020)
The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase, Cerqueira, N. M., Gonzalez P. J., Brondino C. D., Romao M. J., Romao C. C., Moura I., and Moura J. J. , J Comput Chem, Nov 30, Volume 30, Number 15, p.2466-84, (2009) AbstractWebsite

The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton-electron transfer stage, where the Mo(V) species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo-dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with Mo(VI) ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl-dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur-based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of Mo(V) species. Mo(VI) intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the Mo(VI) species allow water molecule dissociation, and, the concomitant enzymatic turnover.

Effects of bilirubin molecular species on membrane dynamic properties of human erythrocyte membranes: a spin label electron paramagnetic resonance spectroscopy study, Brito, M. A., Brondino C. D., Moura J. J., and Brites D. , Arch Biochem Biophys, Mar 1, Volume 387, Number 1, p.57-65, (2001) AbstractWebsite

Unconjugated bilirubin is a neurotoxic pigment that interacts with membrane lipids. In this study we used electron paramagnetic resonance and the spin labels 5-, 7-, 12-, and 16-doxyl-stearic acid (DSA) to evaluate the depth of the hydrocarbon chain at which interaction of bilirubin preferentially occurs. In addition, we used different pH values to determine the molecular species involved. Resealed right-side-out ghosts were incubated (1-60 min) with bilirubin (3.4-42.8 microM) at pH 7.0, 7.4, and 8.0. Alterations of membrane dynamic properties were maximum after 15 min of incubation with 8.6 microM bilirubin at pH 7.4 and were accompanied by a significant release of phospholipids. Interestingly, concentrations of bilirubin up to 42.8 microM and longer incubations resulted in the elution of cholesterol and further increased that of phospholipids while inducing less structural alterations. Variation of the pH values from 8.0 to 7.4 and 7.0, under conditions of maximum perturbation, led to a change from an increased to a diminished polarity sensed by 5-DSA. Conversely, a progressive enhancement in fluidity was reported by 7-DSA, followed by 12- and 16-DSA. These results indicate that bilirubin while enhancing membrane lipid order at C-5 simultaneously has disordering effects at C-7. Furthermore, recovery of membrane dynamics after 15 min of bilirubin exposure along with the release of lipids is compatible with a membrane adaptive response to the insult. In addition, our data provide evidence that uncharged diacid is the species primarily interacting with the membrane as perturbation is favored by acidosis, a condition frequently associated with hyperbilirubinemia in premature and severely ill infants.

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.

An efficient non-mediated amperometric biosensor for nitrite determination, Silveira, C. M., Gomes S. P., Araujo A. N., Montenegro M. C., Todorovic S., Viana A. S., Silva R. J., Moura J. J., and Almeida M. G. , Biosens Bioelectron, May 15, Volume 25, Number 9, p.2026-32, (2010) AbstractWebsite

In this paper we propose the construction of a new non-mediated electrochemical biosensor for nitrite determination in complex samples. The device is based on the stable and selective cytochrome c nitrite reductase (ccNiR) from Desulfovibrio desulfuricans, which has both high turnover and heterogeneous electron transfer rates. In opposition to previous efforts making use of several redox mediators, in this work we exploited the capacity of ccNiR to display a direct electrochemical response when interacting with pyrolytic graphite (PG) surfaces. To enable the analytical application of such bioelectrode the protein was successfully incorporated within a porous silica glass made by the sol-gel process. In the presence of nitrite, the ccNiR/sol-gel/PG electrode promptly displays catalytic currents indicating that the entrapped ccNiR molecules are reduced via direct electron transfer. This result is noteworthy since the protein molecules are caged inside a non-conductive silica network, in the absence of any mediator species or electron relay. At optimal conditions, the minimum detectable concentration is 120 nM. The biosensor sensitivity is 430 mA M(-1) cm(-2) within a linear range of 0.25-50 microM, keeping a stable response up to two weeks. The analysis of nitrites in freshwaters using the method of standard addition was highly accurated.

An efficient poly(pyrrole-viologen)-nitrite reductase biosensor for the mediated detection of nitrite, Da Silva, S., Cosnier S., Almeida M. G., and Moura J. J. G. , Electrochemistry Communications, Apr, Volume 6, Number 4, p.404-408, (2004) AbstractWebsite

A biosensor for nitrite analytical determination was developed using a cytochrome c nitrite reductase (ccNiR) from Desulfovibrio desufuricans ATCC 27774 immobilized and electrically connected on a glassy carbon electrode by entrapment in an electrogencrated poly(pyrrole-viologen) matrix. The modified bioelectrode was studied by cyclic voltammetry and a catalytic current was observed in presence of nitrite. The linear range of the electrode response was 5.4-43.4 muM. The detection limit and the sensitivity were 5.4 muM and 1721 mA M-1 cm(-2), respectively. The K-M(app) value determined from the Lineweaver-Burk plot was 86 muM. The biosensor fully maintained its electroenzymatic activity towards nitrite after four days.. No catalytic response was observed in the presence of nitrate ions while interference from sulfites was considered negligible. Finally, the biosensor composition was optimized in term of monomer-enzyme ratio. (C) 2004 Elsevier B.V. All rights reserved.

Electroanalytical characterization of the direct Marinobacter hydrocarbonoclasticus nitric oxide reductase-catalysed nitric oxide and dioxygen reduction, Gomes, F., Maia L., Cordas C., Moura I., Delerue-Matos C., Moura J. J. G., and Morais S. , Bioelectrochem, Volume 125, p.8-14, (2019) Website
Electrochemical behavior of bacterial nitric oxide reductase – evidences of low redox potential non-heme FeB give new perspectives on the catalytic mechanism, Cordas, C. M., Duarte A. G.,.Moura J. J. G., and Moura I. , Biochim Biophys Acta, Volume 1827, p.233-238, (2013)
Electrochemical studies of rubredoxin from Desulfovibrio vulgaris at modified electrodes, Correia dos Santos, M. M., Paes de Sousa P. M., Simões Gonçalves M. L., Ascenso C., Moura I., and Moura J. J. G. , Journal of Electroanalytical Chemistry, Volume 501, Number 1–2, p.173-179, (2001) AbstractWebsite
Electrochemical studies of the hexaheme nitrite reductase from Desulfovibrio desulfuricans ATCC 27774, Moreno, C., Costa C., Moura I., Legall J., Liu M. Y., Payne W. J., Van Dijk C., and Moura J. J. , Eur J Biochem, Feb 15, Volume 212, Number 1, p.79-86, (1993) AbstractWebsite

The electron-transfer kinetics between three different mediators and the hexahemic enzyme nitrite reductase isolated from Desulfovibrio desulfuricans (ATCC 27774) were investigated by cyclic voltammetry and by chronoamperometry. The mediators, methyl viologen, Desulfovibrio vulgaris (Hildenborough) cytochrome c3 and D. desulfuricans (ATCC 27774) cytochrome c3 differ in structure, redox potential and charge. The reduced form of each mediator exchanged electrons with nitrite reductase. Second-order rate constants, k, were calculated on the basis of the theory for a simple catalytic mechanism and the results, obtained by cyclic voltammetry, were compared with those obtained by chronoamperometry. Values for k are in the range 10(6)-10(8) M-1 s-1 and increase in the direction D. desulfuricans cytochrome c3-->D. vulgaris cytochrome c3-->methyl viologen. An explanation is advanced on the basis of electrostatic interactions and relative orientation between the partners involved. Chronoamperometry (computer controlled) offers advantages over cyclic voltammetry in the determination of homogeneous rate constants (faster, more accurate and better reproducibility). Direct, unmediated electrochemical responses of the hexaheme nitrite reductase were also reported.

Electrochemical studies on c-type cytochromes at microelectrodes, Correia dos Santos, M. M., Paes de Sousa P. M., Simões Gonçalves M. L., Lopes H., Moura I., and Moura J. J. G. , Journal of Electroanalytical Chemistry, Volume 464, Number 1, p.76-84, (1999) AbstractWebsite
Electrochemical studies on nitrite reductase towards a biosensor, Scharf, M., Moreno C., Costa C., Van Dijk C., Payne W. J., Legall J., Moura I., and Moura J. J. , Biochem Biophys Res Commun, Apr 26, Volume 209, Number 3, p.1018-25, (1995) AbstractWebsite

A c-type hexaheme nitrite reductase (NiR) isolated from nitrate-grown cells of Desulfovibrio desulfuricans (Dd) ATCC 27774 catalyses the six-electron reduction of nitrite to ammonia. Previous electrochemical studies demonstrated that a simple electrocatalytic mechanism can be applied to this system (Moreno, C., Costa, C., Moura, I., LeGall, J., Liu, M. Y., Payne, W. J., Van Dijk, C. and Moura, J. J. G. (1992) Eur.J.Biochem. 212, 79-86). Its substrate specificity, availability and stability under ambient conditions makes this enzymatic system a promising candidate for use in a biosensor device. An electrochemical study of gel-immobilized Dd NiR on a glassy carbon electrode revealed both enzymatic activity and amperometric response to nitrite. In this study it was observed that the catalytic current density is a function of the nitrite concentration in solution and follows a characteristic Michaelis-Menten-type substrate dependence. Such a biosensor device (NiR-electrode) bears the option to be used for analytical determination of nitrite in complex media.

Electrochemical studies on small electron transfer proteins using membrane electrodes, dos Santos, M. M. C., de Sousa P. M. P., Goncalves M. L. S., Krippahl L., Moura J. J. G., Lojou E., and Bianco P. , Journal of Electroanalytical Chemistry, Jan 16, Volume 541, p.153-162, (2003) AbstractWebsite

Membrane electrodes (ME) were constructed using gold, glassy carbon and pyrolytic graphite supports and a dialysis membrane, and used to study the electrochemical behavior of small size electron transfer proteins: monohemic cytochrome c(522) from Pseudomonas nautica and cytochrome c(533) as well as rubredoxin from Desulfovibrio vulgaris. Different electrochemical techniques were used including cyclic voltammetry (CV), square wave voltammetry (SW) and differential pulse voltammetry (DP). A direct electrochemical response was obtained in all cases except with rubredoxin where a facilitator was added to the protein solution entrapped between the membrane and the electrode surface. Formal potentials and heterogeneous charge transfer rate constants were determined from the voltammetric data. The influence of the ionic strength and the pH of the medium on the electrochemical response at the ME were analyzed. The benefits from the use of the ME in protein electrochemistry and its role in modulating the redox behavior are analyzed. A critical comparison is presented with data obtained at non-MEs. Finally, the interactions that must be established between the proteins and the electrode surfaces are discussed, thereby modeling molecular interactions that occur in biological systems. (C) 2002 Elsevier Science B.V. All rights reserved.

Electrochemical study on cytochrome c peroxidase from Paracoccus denitrificans: a shifting pattern of structural and thermodynamic properties as the enzyme is activated, Lopes, H., Pettigrew G. W., Moura I., and Moura J. J. G. , Journal of Biological Inorganic Chemistry, Dec, Volume 3, Number 6, p.632-642, (1998) AbstractWebsite

The di-haem cytochrome c peroxidase of Paracoccus denitrificans is a calcium binding dimer of 37.5 kDa subunits. It is responsible for reduction of H(2)O(2) to H(2)O with oxidation of cytochrome c(550) and is isolated in a fully oxidised state (inactive) in which one haem (centre I) is in a high-spin/low-spin equilibrium and high potential and the other (centre II) is low-spin and low potential. The enzyme undergoes direct electron transfer (without the need for mediators) with a 4,4'-dithiodipyridine-modified gold electrode and the response of both haem groups can be observed. By combination of the cyclic and pulse voltammetric data with the established spectroscopic information, it was demonstrated that entry of one electron to the high potential haem leads (in a mechanism involving strong haem-haem interactions) to a complex change of spin states and redox potentials of both haems in order to attain a "ready state" for binding, reduction and cleavage of the hydrogen peroxide. In the absence of endogenous calcium, haem communication can be completely disconnected and is recovered only when Ca(2+) is added, an essential step for the formation of the peroxidatic site. The intricate electrochemical behaviour of this enzyme was interpreted as a mechanism involving, both reduction and oxidation of the high potential haem, an interfacial electron transfer coupled to a homogenous chemical reaction (EC mechanism). We discuss two different models for the sequence of events leading to the appearance of the active pentacoordinated peroxidatic haem.

Electrode Kinetics of Ion Jelly and Ion Sol-Gel Redox Materials on Screen-Printed Electrodes, Carvalho, R. N. H., Cordas C. M., and Fonseca L. P. , Appl Sci, Volume 12, p.2087, (2022)
Electron paramagnetic resonance studies on the mechanism of activation and the catalytic cycle of the nickel-containing hydrogenase from Desulfovibrio gigas, Teixeira, M., Moura I., Xavier A. V., Huynh B. H., Dervartanian D. V., Peck, H. D. Jr., Legall J., and Moura J. J. , J Biol Chem, Jul 25, Volume 260, Number 15, p.8942-50, (1985) AbstractWebsite

Desulfovibrio gigas hydrogenase (EC is a complex enzyme containing one nickel, one 3Fe, and two [Fe4S4] clusters (Teixeira, M., Moura, I., Xavier, A. V., Der Vartanian, D. V., LeGall, J., Peck, H. D., Jr., Huynh, B. H., and Moura, J. J. G. (1983) Eur. J. Biochem. 130, 481-484). This hydrogenase belongs to a class of enzymes that are inactive "as isolated" (the so-called "oxygen-stable hydrogenases") and must go through an activation process in order to express full activity. The state of characterization of the active centers of the enzyme as isolated prompted us to do a detailed analysis of the redox patterns, activation profile, and catalytic redox cycle of the enzyme in the presence of either the natural substrate (H2) or chemical reductants. The effect of natural cofactors, as cytochrome C3, was also studied. Special focus was given to the intermediate redox species generated during the catalytic cycle of the enzyme and to the midpoint redox potentials associated. The available information is discussed in terms of a "working hypothesis" for the mechanism of the [NiFe] hydrogenases from sulfate reducing organisms in the context of activation process and catalytic cycle.

Electron transfer and docking between cytochrome cd1 nitrite reductase and different redox partners - A comparative study, Pedroso, H. A., Silveira C. M., Almeida R. M., Almeida A., Besson S., Moura I., Moura J. J. G., and Almeida M. G. , Biochim Biophys Acta, Volume 1857, p.1412-142104.279, (2016) Website
Electron transfer and molecular recognition in denitrification and nitrate dissimilatory pathways, Almeida, R. M., Dell'Acqua S., Moura I., Pauleta S. R., and Moura J. J. G. , Metalloenzymes in Denitrification: Applications and Environmental Impacts, RSC Metallobiology Series No. 9 (ISBN: 978-1-78262-376-2)., p.252-286, (2017)
Electron transfer complex between nitrous oxide reductase and cytochrome c552 from Pseudomonas nautica: kinetic, nuclear magnetic resonance, and docking studies, Dell'Acqua, S., Pauleta S. R., Monzani E., Pereira A. S., Casella L., Moura J. J., and Moura I. , Biochemistry, Oct 14, Volume 47, Number 41, p.10852-62, (2008) AbstractWebsite

The multicopper enzyme nitrous oxide reductase (N 2OR) catalyzes the final step of denitrification, the two-electron reduction of N 2O to N 2. This enzyme is a functional homodimer containing two different multicopper sites: CuA and CuZ. CuA is a binuclear copper site that transfers electrons to the tetranuclear copper sulfide CuZ, the catalytic site. In this study, Pseudomonas nautica cytochrome c 552 was identified as the physiological electron donor. The kinetic data show differences when physiological and artificial electron donors are compared [cytochrome vs methylviologen (MV)]. In the presence of cytochrome c 552, the reaction rate is dependent on the ET reaction and independent of the N 2O concentration. With MV, electron donation is faster than substrate reduction. From the study of cytochrome c 552 concentration dependence, we estimate the following kinetic parameters: K m c 552 = 50.2 +/- 9.0 muM and V max c 552 = 1.8 +/- 0.6 units/mg. The N 2O concentration dependence indicates a K mN 2 O of 14.0 +/- 2.9 muM using MV as the electron donor. The pH effect on the kinetic parameters is different when MV or cytochrome c 552 is used as the electron donor (p K a = 6.6 or 8.3, respectively). The kinetic study also revealed the hydrophobic nature of the interaction, and direct electron transfer studies showed that CuA is the center that receives electrons from the physiological electron donor. The formation of the electron transfer complex was observed by (1)H NMR protein-protein titrations and was modeled with a molecular docking program (BiGGER). The proposed docked complexes corroborated the ET studies giving a large number of solutions in which cytochrome c 552 is placed near a hydrophobic patch located around the CuA center.

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.

Electron transfer complexes of cytochrome c peroxidase from Paracoccus denitrificans containing more than one cytochrome, Pettigrew, G. W., Pauleta S. R., Goodhew C. F., Cooper A., Nutley M., Jumel K., Harding S. E., Costa C., Krippahl L., Moura I., and Moura J. , Biochemistry, Oct 21, Volume 42, Number 41, p.11968-81, (2003) AbstractWebsite

According to the model proposed in previous papers [Pettigrew, G. W., Prazeres, S., Costa, C., Palma, N., Krippahl, L., and Moura, J. J. (1999) The structure of an electron-transfer complex containing a cytochrome c and a peroxidase, J. Biol. Chem. 274, 11383-11389; Pettigrew, G. W., Goodhew, C. F., Cooper, A., Nutley, M., Jumel, K., and Harding, S. E. (2003) Electron transfer complexes of cytochrome c peroxidase from Paracoccus denitrificans, Biochemistry 42, 2046-2055], cytochrome c peroxidase of Paracoccus denitrificans can accommodate horse cytochrome c and Paracoccus cytochrome c(550) at different sites on its molecular surface. Here we use (1)H NMR spectroscopy, analytical ultracentrifugation, molecular docking simulation, and microcalorimetry to investigate whether these small cytochromes can be accommodated simultaneously in the formation of a ternary complex. The pattern of perturbation of heme methyl and methionine methyl resonances in binary and ternary solutions shows that a ternary complex can be formed, and this is confirmed by the increase in the sedimentation coefficient upon addition of horse cytochrome c to a solution in which cytochrome c(550) fully occupies its binding site on cytochrome c peroxidase. Docking experiments in which favored binary solutions of cytochrome c(550) bound to cytochrome c peroxidase act as targets for horse cytochrome c and the reciprocal experiments in which favored binary solutions of horse cytochrome c bound to cytochrome c peroxidase act as targets for cytochrome c(550) show that the enzyme can accommodate both cytochromes at the same time on adjacent sites. Microcalorimetric titrations are difficult to interpret but are consistent with a weakened binding of horse cytochrome c to a binary complex of cytochrome c peroxidase and cytochrome c(550) and binding of cytochrome c(550) to the cytochrome c peroxidase that is affected little by the presence of horse cytochrome c in the other site. The presence of a substantial capture surface for small cytochromes on the cytochrome c peroxidase has implications for rate enhancement mechanisms which ensure that the two electrons required for re-reduction of the enzyme after reaction with hydrogen peroxide are delivered efficiently.

Electron transfer mechanism studies of cytochrome c3: pH dependence of the redox equilibria, Santos, H., Moura J. J. G., Xavier A. V., and Legall J. , Inorganica Chimica Acta, Volume 79, p.167-169, (1983) AbstractWebsite
Electron transport in sulfate-reducing bacteria. Molecular modeling and NMR studies of the rubredoxin--tetraheme-cytochrome-c3 complex, Stewart, D. E., Legall J., Moura I., Moura J. J., Peck, H. D. Jr., Xavier A. V., Weiner P. K., and Wampler J. E. , Eur J Biochem, Nov 20, Volume 185, Number 3, p.695-700, (1989) AbstractWebsite

A hypothetical model of the complex formed between the iron-sulfur protein rubredoxin and the tetraheme cytochrome c3 from the sulfate-reducing bacteria Desulfovibrio vulgaris (Hildenborough) has been proposed utilizing computer graphic modeling, computational methods and NMR spectroscopy. The proposed complex appears feasible on the basis of complementary electrostatic interaction and steric factors and is consistent with the data from NMR experiments. In this model, the non-heme iron atom of rubredoxin is in close proximity to heme 1 of cytochrome c3. The complex is stabilized by charge-pair interactions and hydrogen bonds. This complex is compared to the flavodoxin-cytochrome c3 complex previously proposed [Stewart, D. E., LeGall, J., Moura, I., Moura, J. J. G., Peck, H. D. Jr, Xavier, A. V., Weiner, P. K. & Wampler, J. E. (1988) Biochemistry 27, 2444-2450] and new NMR data shows that both proteins interact with the same heme group of the cytochrome as postulated.

Electronic and magnetic properties of nickel-substituted rubredoxin: a variable-temperature magnetic circular dichroism study, Kowal, Andrzej T., Zambrano Isabel C., Moura Isabel, Moura Jose J. G., Legall Jean, and Johnson Michael K. , Inorganic Chemistry, 1988/04/01, Volume 27, Number 7, p.1162-1166, (1988) AbstractWebsite
Electronic structure description of the mu(4)-sulfide bridged tetranuclear Cu(Z) center in N(2)O reductase, Chen, P., DeBeer George S., Cabrito I., Antholine W. E., Moura J. J., Moura I., Hedman B., Hodgson K. O., and Solomon E. I. , J Am Chem Soc, Feb 6, Volume 124, Number 5, p.744-5, (2002) AbstractWebsite

Spectroscopy coupled with density functional calculations has been used to define the spin state, oxidation states, spin distribution, and ground state wave function of the mu4-sulfide bridged tetranuclear CuZ cluster of nitrous oxide reductase. Initial insight into the electronic contribution to N2O reduction is developed, which involves a sigma superexchange pathway through the bridging sulfide.