[CD4+, CD8+ AND CD19+ cells in individuals with dyslipidemia]. / Populações Celulares Periféricas (CD4+, CD8+ e CD19+) em Indivíduos Dislipidémicos.

INTRODUCTION: The past decade has witnessed an increasing recognition that inflammatory mechanisms play a central role in the pathogenesis of atherosclerosis and its complications. Recently, attention was focused on the potential role of plasma markers of inflammation as risk predictors among those at risk for cardiovascular events. Of these potential markers, C-reactive protein (CRP), IL6, metalloproteinases, ICAM, VCAM and other molecules, have been extensively studied. On the other hand, to our knowledge, there are only a few studies on the role of inflammatory cells, like T and B lymphocytes in the atherosclerosis. MATERIAL AND METHODS: By flow cytometry analysis we have determined on dyslipidemic people and on a control group, the percentage of some peripheral inflammatory cells, like CD3+, CD4+, CD8+, CD19+, CD56+, CD56CD8+, DN, CD25+, CD26+, CD25CD3+, CD26CD3+, CD25CD26CD3+, CCR5+, CCR5CD3+, CCR5CD4+, HLADR+, HLADRCD4+, HLADRCD8h+, HLADRCD8low+, HLADRCD8+, CD95+, CD95CD95L+, CD3CD95+, CD3CD95L+, CD62L+, CD3CD62L+, CD69+, CD69CD3+ e CD69CD4+. RESULTS: In the present study we have particularly studied the percentage of CD4+, CD8+ and CD19+ cells. The CD4+ cells have been significantly reduced in the people with dyslipidemia. DISCUSSION: We do not know the peripheral numbers of the subtype Th1 and Th2, neither the percentage of CD4+CD25+ cells (regulatory T cells). We have not find any differences on the percentage from the CD8+ and CD19+ cells. CONCLUSIONS: In spite of the identified limitations resulting from the small-sized samples, it was possible to show a reduction of some molecules after application of acetylsalicylic acid.

Introdução: Os mecanismos imunológicos e inflamatórios têm um papel crucial no desenvolvimento da aterosclerose e na sua tradução clínica. São inúmeros os estudos que procuraram relacionar os mais diversos marcadores inflamatórios ­ leucócitos, proteína C reactiva, interleucinas, quimiocinas, moléculas de adesão, metaloproteinases, etc ­ com os factores de risco clássicos da aterosclerose, a formação da placa e os fenómenos clínicos. Não são tantos, que tenhamos conhecimento, os trabalhos que analisaram o comportamento das diversas células mononucleares na fisiopatologia da aterosclerose. Sendo os monócitos/macrófagos e os linfócitos células fundamentais no desencadear e posterior evolução desta doença vascular, procurámos determinar as percentagens das diversas populações celulares periféricas em indivíduos dislipidémicos e em normolipidémicos.Material e Métodos: Por citometria de fluxo, determinámos em indivíduos com dislipidemia e num grupo controlo, as concentrações no sangue periférico dos CD3+, CD4+, CD8+, CD19+, CD56+, CD56CD8+, DN, CD25+, CD26+, CD25CD3+, CD26CD3+, CD25CD26CD3+, CCR5+, CCR5CD3+, CCR5CD4+, HLADR+, HLADRCD4+, HLADRCD8h+, HLADRCD8low+, HLADRCD8+, CD95+, CD95CD95L+, CD3CD95+, CD3CD95L+, CD62L+, CD3CD62L+, CD69+, CD69CD3+ e CD69CD4+. Resultados: Embora na sua grande maioria não tenham sido encontradas diferenças significativas entre os dois grupos de participantes, verificaram-se em algumas populações celulares, resultados que nos mereceram alguns comentários. Neste artigo debruçámo-nos apenas sobre as populações positivas para os CD4, CD8 e CD19.Discussão: A menor concentração das células CD4+ na nossa população de dislipidémicos foi aparentemente inesperada devido ao relacionamento existente entre este tipo celular, os factores de risco e a aterosclerose. Não foram determinados os subtipos Th1 e Th2, nem a população de células reguladoras CD4+CD25+, que poderiam explicar a menor percentagem de células CD4+ nos nossos dislipidémicos. Relativamente às células CD8+ e CD19+, apresentaram percentagens sobreponíveis nos dois grupos de participantes.Conclusões: Apesar das limitações evidenciadas em resultado da reduzida dimensão das populações, foi possível demonstrar uma redução em algumas moléculas após aplicação de ácido acetilsalicílico.

Recent advances into vanadyl, vanadate and decavanadate interactions with actin.

Although the number of papers about "vanadium" has doubled in the last decade, the studies about "vanadium and actin" are scarce. In the present review, the effects of vanadyl, vanadate and decavanadate on actin structure and function are compared. Decavanadate (51)V NMR signals, at -516 ppm, broadened and decreased in intensity upon actin titration, whereas no effects were observed for vanadate monomers, at -560 ppm. Decavanadate is the only species inducing actin cysteine oxidation and vanadyl formation, both processes being prevented by the natural ligand of the protein, ATP. Vanadyl titration with monomeric actin (G-actin), analysed by EPR spectroscopy, reveals a 1:1 binding stoichiometry and a K(d) of 7.5 µM(-1). Both decavanadate and vanadyl inhibited G-actin polymerization into actin filaments (F-actin), with a IC(50) of 68 and 300 µM, respectively, as analysed by light scattering assays, whereas no effects were detected for vanadate up to 2 mM. However, only vanadyl (up to 200 µM) induces 100% of G-actin intrinsic fluorescence quenching, whereas decavanadate shows an opposite effect, which suggests the presence of vanadyl high affinity actin binding sites. Decavanadate increases (2.6-fold) the actin hydrophobic surface, evaluated using the ANSA probe, whereas vanadyl decreases it (15%). Both vanadium species increased the ε-ATP exchange rate (k = 6.5 × 10(-3) s(-1) and 4.47 × 10(-3) s(-1) for decavanadate and vanadyl, respectively). Finally, (1)H NMR spectra of G-actin treated with 0.1 mM decavanadate clearly indicate that major alterations occur in protein structure, which are much less visible in the presence of ATP, confirming the preventive effect of the nucleotide on the decavanadate interaction with the protein. Putting it all together, it is suggested that actin, which is involved in many cellular processes, might be a potential target not only for decavanadate but above all for vanadyl. By affecting actin structure and function, vanadium can regulate many cellular processes of great physiological significance.

Analysis of the activation mechanism of Pseudomonas stutzeri cytochrome c peroxidase through an electron transfer chain.

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) × 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.

Cooperative use of cytochrome cd1 nitrite reductase and its redox partner cytochrome c552 to improve the selectivity of nitrite biosensing.

In this work, a novel enzymatic biosensor for determination of nitrites constructed on an electrochemical transducing platform is proposed. The sensor is based on cytochrome-cd(1) (cyt-cd(1)) nitrite reductase from Marinobacter hydrocarbonoclasticus strain 617 as biological recognition element, and its putative physiological redox partner cytochrome-c(552) (cyt-c(552)), as electron mediator. The proteins were co-immobilized using a photopolymerizable polyvinyl alcohol (PVA) derivative, onto carbon paste screen printed electrodes (CPSPEs); the optimal modification conditions were 100 µM cyt-cd(1)/100 µM cyt-c(552) and 50% PVA, after a 48 h polymerization time. Electrochemical characterization of the mediator was carried out by cyclic voltammetry. The one-electron exchange between cyt-c(552) and the working electrode is a quasi-reversible process, without mass transport limitations. The formal potential of the mediator is 254±2 mV vs NHE and the intermolecular electron transfer rate constant between cytochromes c(552) and cd(1) is 9.9×10(3)M(-1)s(-1). The analytical parameters of the biosensor response to nitrite as assessed by amperometric measurements were: linear range from 10 to 200 µM; detection and quantification limits of 7 and 24 µM, respectively; sensitivity of 2.49±0.08 Amol(-1)cm(2) µM(-1). Catalytic profiles in the presence of possible interfering species were also investigated. The interference from competitive enzymatic reduction of dissolved oxygen could be overcome by tuning the cyclic voltammograms for faster sweep rates.

Continuous-wave EPR at 275GHz: application to high-spin Fe(3+) systems.

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.

Crystal structure of the zinc-, cobalt-, and iron-containing adenylate kinase from Desulfovibrio gigas: a novel metal-containing adenylate kinase from Gram-negative bacteria.

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 Å, 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.

Cobalt-, zinc- and iron-bound forms of adenylate kinase (AK) from the sulfate-reducing bacterium Desulfovibrio gigas: purification, crystallization and preliminary X-ray diffraction analysis.

Adenylate kinase (AK; ATP:AMP phosphotransferase; EC 2.7.4.3) is involved in the reversible transfer of the terminal phosphate group from ATP to AMP. AKs contribute to the maintenance of a constant level of cellular adenine nucleotides, which is necessary for the energetic metabolism of the cell. Three metal ions, cobalt, zinc and iron(II), have been reported to be present in AKs from some Gram-negative bacteria. Native zinc-containing AK from Desulfovibrio gigas was purified to homogeneity and crystallized. The crystals diffracted to beyond 1.8 A resolution. Furthermore, cobalt- and iron-containing crystal forms of recombinant AK were also obtained and diffracted to 2.0 and 3.0 A resolution, respectively. Zn(2+)-AK and Fe(2+)-AK crystallized in space group I222 with similar unit-cell parameters, whereas Co(2+)-AK crystallized in space group C2; a monomer was present in the asymmetric unit for both the Zn(2+)-AK and Fe(2+)-AK forms and a dimer was present for the Co(2+)-AK form. The structures of the three metal-bound forms of AK will provide new insights into the role and selectivity of the metal in these enzymes.

The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase.

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.

Sarcoplasmic reticulum calcium ATPase is inhibited by organic vanadium coordination compounds: pyridine-2,6-dicarboxylatodioxovanadium(V), BMOV, and an amavadine analogue.

The general affinity of the sarcoplasmic reticulum (SR) Ca (2+)-ATPase was examined for three different classes of vanadium coordination complexes including a vanadium(V) compound, pyridine-2,6-dicarboxylatodioxovanadium(V) (PDC-V(V)), and two vanadium(IV) compounds, bis(maltolato)oxovanadium(IV) (BMOV), and an analogue of amavadine, bis( N-hydroxylamidoiminodiacetato)vanadium(IV) (HAIDA-V(IV)). The ability of vanadate to act either as a phosphate analogue or as a transition-state analogue with enzymes' catalysis phosphoryl group transfer suggests that vanadium coordination compounds may reveal mechanistic preferences in these classes of enzymes. Two of these compounds investigated, PDC-V(V) and BMOV, were hydrolytically and oxidatively reactive at neutral pH, and one, HAIDA-V(IV), does not hydrolyze, oxidize, or otherwise decompose to a measurable extent during the enzyme assay. The SR Ca (2+)-ATPase was inhibited by all three of these complexes. The relative order of inhibition was PDC-V(V) > BMOV > vanadate > HAIDA-V(IV), and the IC 50 values were 25, 40, 80, and 325 microM, respectively. Because the observed inhibition is more potent for PDC-V(V) and BMOV than that of oxovanadates, the inhibition cannot be explained by oxovanadate formation during enzyme assays. Furthermore, the hydrolytically and redox stable amavadine analogue HAIDA-V(IV) inhibited the Ca (2+)-ATPase less than oxovanadates. To gauge the importance of the lipid environment, studies of oxidized BMOV in microemulsions were performed and showed that this system remained in the aqueous pool even though PDC-V(V) is able to penetrate lipid interfaces. These findings suggest that the hydrolytic properties of these complexes may be important in the inhibition of the calcium pump. Our results show that two simple coordination complexes with known insulin enhancing effects can invoke a response in calcium homeostasis and the regulation of muscle contraction through the SR Ca (2+)-ATPase.

Benefits of membrane electrodes in the electrochemistry of metalloproteins: mediated catalysis of Paracoccus pantotrophus cytochrome c peroxidase by horse cytochrome c: a case study.

A comparative study of direct and mediated electrochemistry of metalloproteins in bulk and membrane-entrapped solutions is presented. This work reports the first electrochemical study of the electron transfer between a bacterial cytochrome c peroxidase and horse heart cytochrome c. The mediated catalysis of the peroxidase was analysed both using the membrane electrode configuration and with all proteins in solution. An apparent Michaelis constant of 66 +/- 4 and 42 +/- 5 microM was determined at pH 7.0 and 0 M NaCl for membrane and bulk solutions, respectively. The data revealed that maximum activity occurs at 50 mM NaCl, pH 7.0, with intermolecular rate constants of (4.4 +/- 0.5) x 10(6) and (1.0 +/- 0.5) x 10(6) M(-1) s(-1) for membrane-entrapped and bulk solutions, respectively. The influence of parameters such as pH or ionic strength on the mediated catalytic activity was analysed using this approach, drawing attention to the fact that careful analysis of the results is needed to ensure that no artefacts are introduced by the use of the membrane configuration and/or promoters, and therefore the dependence truly reflects the influence of these parameters on the (mediated) catalysis. From the pH dependence, a pK of 7.5 was estimated for the mediated enzymatic catalysis.

The diseases we cause: Iatrogenic illness in a department of internal medicine.

BACKGROUND: The aim of this study was to estimate the incidence, main causes, and risk factors of iatrogenic disease occurring in a department of internal medicine. METHODS: Over a 1-year period, physicians systematically filled out a 2-page questionnaire for all patients admitted to the ward. A database was created and the data were statistically analyzed. Patients undergoing immunosuppressive, chemo-, or radiation therapy were excluded. Missing data were completed by reviewing the patients' charts. The patients were then divided into two groups: those with and those without iatrogenic disease. The groups were compared using several parameters including gender, age, social features, days of hospitalization, associated illness, functional status, medical impression, prognosis, associated renal or liver function impairment, drugs taken daily, and outcome. In the group with iatrogenic disease, the type, severity, and predictability were also analyzed. RESULTS: Of the 879 patients admitted to the ward, 445 completed questionnaires and were included in the study. A total of 102 patients (22.9%) developed 121 iatrogenic events. Forty-four patients (43.1%) were admitted for iatrogenic illness, 10 (9.8%) developed life-threatening events, and in 3 (6.8%) it was the cause of death. Fifty-eight patients (56.8%) registered 77 episodes of iatrogenic disease during their hospital stay, 20 (19.6%) developed life-threatening events, and 9 (11.7%) died, 4 (5.2%) of an iatrogenic cause (nosocomial infections). Significant differences were found in 20 out of 26 parameters studied (p<0.005 for all cases; 95% confidence interval). Eighteen percent of all iatrogenic disease was severe, 61.9% predictable, 54.5% avoidable, and 59% drug-related, 80% of which was due to side effects or adverse reactions. Infection and metabolic and electrolyte disorders were the most frequent effects. CONCLUSIONS: It is possible to identify risk factors for iatrogenic events. Chronically ill elderly inpatients are the main target of iatrogenic events.

Mediated catalysis of Paracoccus pantotrophus cytochrome c peroxidase by P. pantotrophus pseudoazurin: kinetics of intermolecular electron transfer.

This work reports the direct electrochemistry of Paracoccus pantotrophus pseudoazurin and the mediated catalysis of cytochrome c peroxidase from the same organism. The voltammetric behaviour was examined at a gold membrane electrode, and the studies were performed in the presence of calcium to enable the peroxidase activation. A formal reduction potential, E (0)', of 230 +/- 5 mV was determined for pseudoazurin at pH 7.0. Its voltammetric signal presented a pH dependence, defined by pK values of 6.5 and 10.5 in the oxidised state and 7.2 in the reduced state, and was constant up to 1 M NaCl. This small copper protein was shown to be competent as an electron donor to cytochrome c peroxidase and the kinetics of intermolecular electron transfer was analysed. A second-order rate constant of 1.4 +/- 0.2 x 10(5) M(-1) s(-1) was determined at 0 M NaCl. This parameter has a maximum at 0.3 M NaCl and is pH-independent between pH 5 and 9.

Vanadium distribution, lipid peroxidation and oxidative stress markers upon decavanadate in vivo administration.

The contribution of decameric vanadate species to vanadate toxic effects in cardiac muscle was studied following an intravenous administration of a decavanadate solution (1mM total vanadium) in Sparus aurata. Although decameric vanadate is unstable in the assay medium, it decomposes with a half-life time of 16 allowing studying its effects not only in vitro but also in vivo. After 1, 6 and 12h upon decavanadate administration the increase of vanadium in blood plasma, red blood cells and in cardiac mitochondria and cytosol is not affected in comparison to the administration of a metavanadate solution containing labile oxovanadates. Cardiac tissue lipid peroxidation increases up to 20%, 1, 6 and 12h after metavanadate administration, whilst for decavanadate no effects were observed except 1h after treatment (+20%). Metavanadate administration clearly differs from decavanadate by enhancing, 12h after exposure, mitochondrial superoxide dismutase (SOD) activity (+115%) and not affecting catalase (CAT) activity whereas decavanadate increases SOD activity by 20% and decreases (-55%) mitochondrial CAT activity. At early times of exposure, 1 and 6h, the only effect observed upon decavanadate administration was the increase by 20% of SOD activity. In conclusion, decavanadate has a different response pattern of lipid peroxidation and oxidative stress markers, in spite of the same vanadium distribution in cardiac cells observed after decavanadate and metavanadate administration. It is suggested that once formed decameric vanadate species has a different reactivity than vanadate, thus, pointing out that the differential contribution of vanadium oligomers should be taken into account to rationalize in vivo vanadate toxicity.

Metabolic syndrome in dyslipidemia consultations.

AIMS: To evaluate the prevalence of the metabolic syndrome (MS) in dyslipidemia consultations, according to the criteria established by the National Cholesterol Education Program Adult Treatment Panel III (ATP III); to classify patients with MS according to ATP III risk categories and prevention type (primary versus secondary); and to evaluate evolution to type 2 diabetes in these patients. METHODS: A retrospective study was conducted based on analysis of the clinical records of 470 patients followed in dyslipidemia consultations at Internal Medicine II of Coimbra University Hospitals. MS was defined as the presence of three or more of the following abnormalities: waist circumference > 102/88 cm (male/female), triglyceride levels > or =150 mg/dl, HDL-cholesterol level < 40/50 mg/dl (male/female), blood pressure > or = 130/85 mmHg and fasting glucose > or = 110 mg/dl. The patients were classified into three risk categories according to the major risk factors defined by ATP III, regardless of LDL-cholesterol level. RESULTS: MS was diagnosed in 31.3% of the patients; 53.7% were male and mean age was 52.7+/-11.9 years. The most prevalent anomaly was hypertriglyceridemia (95.9%), followed by waist circumference (76.1%), HDL cholesterol (73.5%), blood pressure (69.4%) and fasting glycemia (36.7%). Based on the risk categories identified by ATP III, 30.6% of the patients had no or only one risk factor, 66.7% had multiple (2 or more) risk factors and 2.7% had coronary disease or an equivalent risk profile. 97.3% of the patients with MS were in primary prevention. 18.4% developed diabetes, the majority within 1-3 years of the first consultation. CONCLUSIONS: Our study identified a high MS prevalence in patients followed in dyslipidemia consultations, particularly in older age-groups. More than half of the MS patients had an intermediate risk profile and most of them were in primary prevention. We also found that a fifth of non-diabetic patients developed diabetes during follow-up.

Redox chemistry of low-pH forms of tetrahemic cytochrome c3.

Desulfovibrio vulgaris Hildenborough cytochrome c(3) contains four hemes in a low-spin state with bis-histidinyl coordination. High-spin forms of cytochrome c(3) can be generated by protonation of the axial ligands in order to probe spin equilibrium (low-spin/high-spin). The spin alterations occurring at acid pH, the associated changes in redox potentials, as well as the reactivity towards external ligands were followed by the conjunction of square wave voltammetry and UV-visible, CD, NMR and EPR spectroscopies. These processes may be used for modelling the action of enzymes that use spin equilibrium to promote enzyme activity and reactivity towards small molecules.

Metalloenzymes of the denitrification pathway.

Denitrification, or dissimilative nitrate reduction, is an anaerobic process used by some bacteria for energy generation. This process is important in many aspects, but its environmental implications have been given particular relevance. Nitrate accumulation and release of nitrous oxide in the atmosphere due to excess use of fertilizers in agriculture are examples of two environmental problems where denitrification plays a central role. The reduction of nitrate to nitrogen gas is accomplished by four different types of metalloenzymes in four simple steps: nitrate is reduced to nitrite, then to nitric oxide, followed by the reduction to nitrous oxide and by a final reduction to dinitrogen. In this manuscript we present a concise updated review of the bioinorganic aspects of denitrification.

Bacterial nitrate reductases: Molecular and biological aspects of nitrate reduction.

Nitrogen is a vital component in living organisms as it participates in the making of essential biomolecules such as proteins, nucleic acids, etc. In the biosphere, nitrogen cycles between the oxidation states +V and -III producing many species that constitute the biogeochemical cycle of nitrogen. All reductive branches of this cycle involve the conversion of nitrate to nitrite, which is catalyzed by the enzyme nitrate reductase. The characterization of nitrate reductases from prokaryotic organisms has allowed us to gain considerable information on the molecular basis of nitrate reduction. Prokaryotic nitrate reductases are mononuclear Mo-containing enzymes sub-grouped as respiratory nitrate reductases, periplasmic nitrate reductases and assimilatory nitrate reductases. We review here the biological and molecular properties of these three enzymes along with their gene organization and expression, which are necessary to understand the biological processes involved in nitrate reduction.

The methylenetetrahydrofolate reductase (MTHFR) 677C-->T mutation and cardiovascular risk--A case of ischemic stroke and acute myocardial infarction.

The authors report the case of a 39-year-old male patient who had an ischemic stroke (complete infarction of right anterior cerebral circulation) and an acute myocardial infarction during the same year. Molecular study revealed he was homozygous for the 677C-->T mutation in the gene coding for methylenetetrahydrofolate reductase, a key enzyme of folate metabolism; deficiency of this enzyme is associated with increased cardiovascular risk and neurological lesions. Some considerations are put forward about hyperhomocysteinemia and the MTHFR 677C-->T mutation as cardiovascular risk factors.

Antagonists Mo and Cu in a heterometallic cluster present on a novel protein (orange protein) isolated from Desulfovibrio gigas.

An orange-coloured protein (ORP) isolated from Desulfovibrio gigas, a sulphate reducer, has been previously shown by extended X-ray absorption fine structure (EXAFS) to contain a novel mixed-metal sulphide cluster of the type [S(2)MoS(2)CuS(2)MoS(2)] [J. Am. Chem. Soc. 122 (2000) 8321]. We report here the purification and the biochemical/spectroscopic characterisation of this novel protein. ORP is a soluble monomeric protein (11.8 kDa). The cluster is non-covalently bound to the polypeptide chain. The presence of a MoS(4)(2-) moiety in the structure of the cofactor contributes with a quite characteristic UV-Vis spectra, exhibiting an orange colour, with intense absorption peaks at 480 and 338 nm. Pure ORP reveals an Abs(480)/Abs(338) ratio of 0.535. The gene sequence coding for ORP as well as the amino acid sequence was determined. The putative biological function of ORP is discussed.