Oxidovanadium(IV), a cationic species (VO(2+)) of vanadium(IV), binds to several proteins, including actin. Upon titration with oxidovanadium(IV), approximately 100% quenching of the intrinsic fluorescence of monomeric actin purified from rabbit skeletal muscle (G-actin) was observed, with a V(50) of 131 muM, whereas for the polymerized form of actin (F-actin) 75% of quenching was obtained and a V(50) value of 320 muM. Stern-Volmer plots were used to estimate an oxidovanadium(IV)-actin dissociation constant, with K(d) of 8.2 muM and 64.1 muM VOSO(4), for G-actin and F-actin, respectively. These studies reveal the presence of a high affinity binding site for oxidovanadium(IV) in actin, producing local conformational changes near the tryptophans most accessible to water in the three-dimensional structure of actin. The actin conformational changes, also confirmed by (1)H NMR, are accompanied by changes in G-actin hydrophobic surface, but not in F-actin. The (1)H NMR spectra of G-actin treated with oxidovanadium(IV) clearly indicates changes in the resonances ascribed to methyl group and aliphatic regions as well as to aromatics and peptide-bond amide region. In parallel, it was verified that oxidovanadium(IV) prevents the G-actin polymerization into F-actin. In the 0-200 muM range, VOSO(4) inhibits 40% of the extent of polymerization with an IC(50) of 15.1 muM, whereas 500 muM VOSO(4) totally suppresses actin polymerization. The data strongly suggest that oxidovanadium(IV) binds to actin at specific binding sites preventing actin polymerization. By affecting actin structure and function, oxidovanadium(IV) might be responsible for many cellular effects described for vanadium.

The isolation and characterization of a new metalloprotein containing Cu and Fe atoms is reported. The as-isolated Cu-Fe protein shows an UV-visible spectrum with absorption bands at 320 nm, 409 nm and 615 nm. Molecular mass of the native protein along with denaturating electrophoresis and mass spectrometry data show that this protein is a multimer consisting of 14+/-1 subunits of 15254.3+/-7.6 Da. Mossbauer spectroscopy data of the as-isolated Cu-Fe protein is consistent with the presence of [2Fe-2S](2+) centers. Data interpretation of the dithionite reduced protein suggest that the metallic cluster could be constituted by two ferromagnetically coupled [2Fe-2S](+) spin delocalized pairs. The biochemical properties of the Cu-Fe protein are similar to the recently reported molybdenum resistance associated protein from Desulfovibrio, D. alaskensis. Furthermore, a BLAST search from the DNA deduced amino acid sequence shows that the Cu-Fe protein has homology with proteins annotated as zinc resistance associated proteins from Desulfovibrio, D. alaskensis, D. vulgaris Hildenborough, D. piger ATCC 29098. These facts suggest a possible role of the Cu-Fe protein in metal tolerance.

The influence of the protein staining used to visualize protein bands, after in-gel protein separation, for the correct identification of proteins by peptide mass fingerprint (PMF) after application of the ultrasonic in-gel protein protocol was studied. Coomassie brilliant blue and silver nitrate, both visible stains, and the fluorescent dyes Sypro Red and Sypro Orange were evaluated. Results obtained after comparison with the overnight in-gel protocol showed that good results, in terms of protein sequence coverage and number of peptides matched, can be obtained with anyone of the four stains studied. Two minutes of enzymatic digestion time was enough for proteins stained with coomassie blue, while 4 min was necessary when silver or Sypro stainings were employed in order to reach equivalent results to those obtained for the overnigh in-gel protein protocol. For the silver nitrate stain, the concentration of silver present in the staining solution must be 0.09% (w/v) to minimize background in the MALDI mass spectra.

A new clean fast (8 min) method for in-solution protein digestion Without detergent or urea for protein identification by peptide mass fingerprint and mass spectrometry-based techniques is Proposed. The new method avoids the use of time consuming desalting procedures entailing the following four steps done under the effect of an ultrasonic field provided by a sonoreactor: denaturation (1 min) in a mixed Solution of water:acetonitrile 1/1 (v/v): protein reduction (1 min); protein alkylation (1 min); and protein digestion (5 min). Five Proteins with masses comprised between 14.4 kDa and 97 kDa and the protein splitsoret cytochrome c from D. desulfuricans ATCC27774, Were Successfully identified with this procedure. No differences were found in the sequence coverage or in the number of peptides matched when the new clean method was compared to another one using urea. Twofold better signal-to-noise ratios were obtained in the MALDI spectra from protein samples prepared with the new method when comparing it with a method using urea. The new digestion method avoids the need to remove salt content and increases throughput (six samples at once) while reducing sample loss and contamination from sample handling. (C) 2008 Elsevier B.V. All rights reserved.

Three ultrasonic energy sources were studied to speed up the sample treatment for in-solution protein identification by peptide mass fingerprint using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Protein reduction, alkylation, and enzymatic digestion steps were done in 15 min. Nine proteins, including zinc resistance-associated protein precursor from Desulfovibrio desulfuricans strain G20 and split-soret cytochrome c from D. desulfuricans ATCC27774 were successfully identified with the new protocol.

A nitrate reductase was solubilized with Triton X-100 from the membranes of Pseudomonas chlororaphis DSM 50135 grown microaerobically in the presence of nitrate. Like other membrane-bound nitrate reductases, it contains three subunits, of 129, 66 (64) and 24 kDa, referred to in the literature as alpha, beta and gamma, respectively. Electrocatalytic studies revealed that only the membrane-bound, not the solubilized form of the enzyme, can accept electrons from a menaquinone analog, menadione, whereas both forms can accept electrons from methylviologen. The isolated enzyme possesses several iron-sulfur clusters and a molybdopterin guanine dinucleotide active center. The iron-sulfur clusters can be grouped in two classes according to their redox properties, the high-potential and low-potential clusters. In the as-isolated enzyme, two forms of the molybdenum center, high- and low-pH, are detectable by electron paramagnetic resonance spectroscopy. The low-pH form shows a hyperfine splitting due to a proton, suggesting the presence of an -OHx ligand. Dithionite reduces the Mo(V) center to Mo(W) and subsequent reoxidization with nitrate originates a new Mo(V) signal, identical to the oxidized low-pH form but lacking its characteristic hyperfine splitting. The isolated preparation also contains heme c (in a sub-stoichiometric amount) with the ability to relay electrons to the molybdenum center, suggesting that this nitrate reductase may contain heme c instead of the heme b usually found in this class of enzymes. (c) 2005 Elsevier B.V. All rights reserved.

Among the biotargets interacting with vanadium is the calcium pump from the sarcoplasmic reticulum (SR). To this end, initial research efforts were launched with two vanadium(V)-citrate complexes, namely (NH(4))(6)[V(2)O(4)(C(6)H(4)O(7))(2)].6H(2)O and (NH(4))(6)[V(2)O(2)(O(2))(2)(C(6)H(4)O(7))(2)].4H(2)O, potentially capable of interacting with the SR calcium pump by combining kinetic studies with (51)V NMR spectroscopy. Upon dissolution in the reaction medium (concentration range: 4-0.5mM), both vanadium(V):citrate (VC) and peroxovanadium(V):citrate (PVC) complexes are partially converted into vanadate oligomers. A 1mM solution of the PVC complex, containing 184microM of the PVC complex, 94microM oxoperoxovanadium(V) (PV) species, 222microM monomeric (V1), 43microM dimeric (V2) and 53microM tetrameric (V4) species, inhibits Ca(2+) accumulation by 75 %, whereas a solution of the VC complex of the same vanadium concentration, containing 98microM of the VC complex, 263microM monomeric (V1), 64microM dimeric (V2) and 92microM tetrameric (V4) species inhibits the calcium pump activity by 33 %. In contrast, a 1 mM metavanadate solution, containing 460microM monomeric (V1), 90.2microM dimeric (V2) and 80microM tetrameric (V4) species, has no effect on Ca(2+) accumulation. The NMR signals from the VC complex (-548.0ppm), PVC complex (-551.5ppm) and PV (-611.1ppm) are broadened upon SR vesicle addition (2.5mg/ml total protein). The relative order for the half width line broadening of the NMR signals, which reflect the interaction with the protein, was found to be V4>PVC>VC>PV>V2=V1=1, with no effect observed for the V1 and V2 signals. Putting it all together the effects of two vanadium(V)-citrate complexes on the modulation of calcium accumulation and ATP hydrolysis by the SR calcium pump reflected the observed variable reactivity into the nature of key species forming upon dissolution of the title complexes in the reaction media.

Extracted human teeth are frequently used for research or educational purposes. Therefore, it is necessary to store them in disinfectant solutions that do not alter dental structures. Thus, this study evaluated the influence of storage solution on enamel demineralization. For that purpose, sixty samples were divided into the following groups: enamel stored in formaldehyde (F1), stored in thymol (T1), stored in formaldehyde and submitted to pH cycling (F2), stored in thymol and submitted to pH cycling (T2). All samples were evaluated by cross-sectional microhardness analysis and had their percentage of mineral volume versus micrometer (integrated area) determined. Differences between groups were found up to 30-microm depth from the enamel surface (p < 0.05), where samples from group T2 were more demineralized. It was concluded that the storage solution influenced the reaction of a dental substrate to a cariogenic challenge, suggesting that formaldehyde may increase enamel resistance to demineralization, when compared to demineralization occurring in enamel stored in thymol solution.

We report the characterization of the molecular properties and EPR studies of a new formate dehydrogenase (FDH) from the sulfate-reducing organism Desulfovibrio alaskensis NCIMB 13491. FDHs are enzymes that catalyze the two-electron oxidation of formate to carbon dioxide in several aerobic and anaerobic organisms. D. alaskensis FDH is a heterodimeric protein with a molecular weight of 126+/-2 kDa composed of two subunits, alpha=93+/-3 kDa and beta=32+/-2 kDa, which contains 6+/-1 Fe/molecule, 0.4+/-0.1 Mo/molecule, 0.3+/-0.1 W/molecule, and 1.3+/-0.1 guanine monophosphate nucleotides. The UV-vis absorption spectrum of D. alaskensis FDH is typical of an iron-sulfur protein with a broad band around 400 nm. Variable-temperature EPR studies performed on reduced samples of D. alaskensis FDH showed the presence of signals associated with the different paramagnetic centers of D. alaskensis FDH. Three rhombic signals having g-values and relaxation behavior characteristic of [4Fe-4S] clusters were observed in the 5-40 K temperature range. Two EPR signals with all the g-values less than two, which accounted for less than 0.1 spin/protein, typical of mononuclear Mo(V) and W(V), respectively, were observed. The signal associated with the W(V) ion has a larger deviation from the free electron g-value, as expected for tungsten in a d(1) configuration, albeit with an unusual relaxation behavior. The EPR parameters of the Mo(V) signal are within the range of values typically found for the slow-type signal observed in several Mo-containing proteins belonging to the xanthine oxidase family of enzymes. Mo(V) resonances are split at temperatures below 50 K by magnetic coupling with one of the Fe/S clusters. The analysis of the inter-center magnetic interaction allowed us to assign the EPR-distinguishable iron-sulfur clusters with those seen in the crystal structure of a homologous enzyme.

The cytochrome c nitrite reductase is isolated from the membranes of the sulfate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774 as a heterooligomeric complex composed by two subunits (61 kDa and 19 kDa) containing c-type hemes, encoded by the genes nrfA and nrfH, respectively. The extracted complex has in average a 2NrfA:1NrfH composition. The separation of ccNiR subunits from one another is accomplished by gel filtration chromatography in the presence of SDS. The amino-acid sequence and biochemical subunits characterization show that NrfA contains five hemes and NrfH four hemes. These considerations enabled the revision of a vast amount of existing spectroscopic data on the NrfHA complex that was not originally well interpreted due to the lack of knowledge on the heme content and the oligomeric enzyme status. Based on EPR and Mossbauer parameters and their correlation to structural information recently obtained from X-ray crystallography on the NrfA structure [Cunha, C.A., Macieira, S., Dias, J.M., Almeida, M.G., Goncalves, L.M.L., Costa, C., Lampreia, J., Huber, R., Moura, J.J.G., Moura, I. & Romao, M. (2003) J. Biol. Chem. 278, 17455-17465], we propose the full assignment of midpoint reduction potentials values to the individual hemes. NrfA contains the high-spin catalytic site (-80 mV) as well as a quite unusual high reduction potential (+150 mV)/low-spin bis-His coordinated heme, considered to be the site where electrons enter. In addition, the reassessment of the spectroscopic data allowed the first partial spectroscopic characterization of the NrfH subunit. The four NrfH hemes are all in a low-spin state (S = 1/2). One of them has a gmax at 3.55, characteristic of bis-histidinyl iron ligands in a noncoplanar arrangement, and has a positive reduction potential.

Metallothioneins (MT) were obtained after purification from metal-exposed clams (Ruditapes decussatus) using gel-permeation and ion-exchange chromatography. Four cadmium-metallothioneins (CdMTs) were resolved by ion-exchange chromatography and they all had similar molecular weights, high cadmium content and an absorption spectra indicative of the presence of characteristic Cd-S aggregates. The NH(2)-terminal sequence suggests the presence of at least two class I clam MT isoforms. For the other two putative clam CdMTs isolated, the results of the amino acid determination were inconclusive. One was slightly contaminated and the other one had a blocked NH(2)-terminal. These clam metalothioneins contain glycine, which seems to be a common feature of molluscan MT family and exhibited more similarity to oysters than to mussels. Further investigation on the inducibility of these isoforms will be necessary if clams are to be used as biomarkers of metal exposure.

In humans, the lymphomyeloid system has a fundamental role on iron metabolism promoting its recycling due to a continuous removal of effete red blood cells. Additionally, one of the most intriguing aspects of metalloporphyrins in biology is their effect on the immune system. However, the process of erythrocyte catabolism is still poorly understood and needs further research. In the present study, we attempt to investigate the nature and the possible physiologic role of Fe compounds released after erythrophagocytosis during the removal of red blood cells. Monocyte erythrophagocytosis in vitro experiments were done to characterize chemically the Fe compounds present inside the cells and in the culture supernatants. We tested the probable immunomodulatory functions of erythrophagocytosis products over lymphocyte cultures activated in vitro with T mitogens (alpha-CD3). Data obtained from atomic absorption spectroscopy confirmed the presence of Fe in the culture supernatants of monocyte cultures after erythrophagocytosis. Also, high-spin haem complexes derived from erythrocyte catabolism were detected by electron paramagnetic electronic resonance. Finally, in vitro activated lymphocyte proliferation experiments indicate the co-mitogenic properties of monocyte culture supernatants after red blood cells phagocytosis. Thus, the results of the present work provide evidence that culture monocyte supernatants after in vitro erythrophagocytosis contain Fe (III) high-spin haem complexes and show lymphocyte proliferation co-stimulatory properties.