Studies on the redox centers of the terminal oxidase from Desulfovibrio gigas and evidence for its interaction with rubredoxin

Abstract: Rubredoxin-oxygen oxidoreductase (ROO) is the final component of a soluble electron transfer chain that couples NADH oxidation to oxygen consumption in the anaerobic sulfate reducer Desulfovibrio gigas. It is an 86-kDa homodimeric flavohemeprotein containing two FAD molecules, one mesoheme IX, and one Fe-uroporphyrin I per monomer, capable of fully reducing oxygen to water. EPR studies on the native enzyme reveal two components with g values at similar to 2.46, 2.29, and 1.89, which are assigned to low spin hemes and are similar to the EPR features of P-450 hemes, suggesting that ROO hemes have a cysteinyl axial ligation. At pH 7.6, the flavin redox transitions occur at 0 +/- 15 mV for the quinone/semiquinone couple and at -130 +/- 15 mV for the semiquinone/hydroquinone couple; the hemes reduction potential is -350 +/- 15 mV. Spectroscopic studies provided unequivocal evidence that the flavins are the electron acceptor centers from rubredoxin, and that their reduction proceed through an anionic semiquinone radical. The reaction with oxygen occurs in the flavin moiety. These data are strongly corroborated by the finding that rubredoxin and ROO are located in the same polycistronic unit of D. gigas genome. For the first time, a clear role for a rubredoxin in a sulfate-reducing bacterium is presented

Desulfovibrio gigas neelaredoxin: a novel superoxide dismutase integrated in a putative oxygen sensory operon of an anaerobe

Neelaredoxin, a small non-heme blue iron protein from the sulfate-reducing bacterium Desulfovibrio gigas [Chen, L., Sharma, P., LeGall, J., Mariano, A.M., Teixeira M. and Xavier, A.V. (1994) Eur. J. Biochem. 226, 613±618] is shown to be encoded by a polycistronic unit which contains two additional open reading frames (ORF-1 and ORF-2) coding for chemotaxis-like proteins. ORF-1 has domains highly homologous with those structurally and functionally important in methyl-accepting chemotaxis proteins, including two putative transmembrane helices, potential methylation sites and the interaction domain with CheW proteins. Interestingly, ORF-2 encodes a protein having homologies with CheW proteins. Neelaredoxin is also shown to have significant superoxide dismutase activity (1200 U´mg±1), making it a novel type of iron superoxide dismutase. Analysis of genomic data shows that neelaredoxin-like putative polypeptides are present in strict anaerobic archaea, suggesting that this is a primordial superoxide dismutase. The three proteins encoded in this operon may be involved in the oxygen-sensing mechanisms of this anaerobic bacterium, indicating a possible transcriptional mechanism to sense and respond to potential stress agents

Growth of melon cultivated under saline stress and potassium doses

O Estado do Rio Grande do Norte, em destaque a região da Chapada do Apodi, se destaca na produção e exportação de melão no País, em regime de irrigação, devido à distribuição pluvial baixa e irregular. A Chapada do Apodi possui dois aqüíferos subterrâneos; a do lençol menos profundo de alta salinidade, porém com menor custo de bombeamento, ocorrendo o contrário com o de maior profundidade. Objetivou-se, ante o exposto, avaliar o efeito de duas águas de salinidades diferentes (0,52 e 2,41 dS m-1), combinadas com cinco doses de K2O (218, 273, 328, 383 e 438 kg ha-1) sobre o crescimento do meloeiro (Cucumis melo L.), cultivar Goldex, utilizando-se do delineamento de blocos ao acaso, com parcelas subdivididas; amostras de planta foram coletadas aos 21, 28, 35, 49 e 63 dias após a semeadura, determinando-se a fitomassa seca das plantas, estas separadas em ramos (caule + folhas), flores e frutos; avaliou-se, também, a taxa de crescimento absoluto e relativo e a produção de frutos. Em geral, o crescimento do melão foi favorecido com o uso de água mais salina; a taxa de crescimento absoluto foi máxima entre 35 e 49 dias após a semeadura. Obteve-se maior produção de fitomassa total com 438 kg ha-1 de K2O e uso de água mais salina, ao final do ciclo.The region of 'Chapada do Apodi', in the State of Rio Grande do Norte, stands out in Brazilian production and exportation of melon. This region possesses two aquiffers, one of lower exploration cost, though of high salinity, another of low salinity, with higher cost and limited use. This work was carried out with the objective to evaluate the effect of waters of different salinities combined with five doses of K in the dry matter accumulation and productivity of the melon (Cucumis melo L.) cultivar Goldex. The experimental design adopted was split plot in completely randomized blocks. The melon crop was irrigated with low (0.52 dS m-1) and high (2.41 dS m-1) salinity water combined with five doses of K2O (218, 273, 328, 383 and 438 kg ha-1). Plants were collected at 21, 28, 35, 49 and 63 days after sowing, and were separated in branches (shoot + leaves), flowers and fruits, and the total dry matter of the aerial parts obtained by summation. The absolute and relative growth rates and the production of fruits were also evaluated. The absolute growth rate of the plant was maximum between 35 and 49 days. The highest total biomass was obtained with 438 kg ha-1 K2O and use of high salinity water at the end of crop cycle.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Chemical Constituents and Evaluation of Antimicrobial and Cytotoxic Activities of Kielmeyera coriacea

Many essential oils (EOs) of different plant species possess interesting antimicrobial effects on buccal microorganisms and cytotoxic properties. EOs of Kielmeyera coriacea Mart. & Zucc. were analyzed by gas chromatography coupled to mass spectrometry (GC-MS). The EO from leaves is rich in sesquiterpenes hydrocarbons and oxygenated sesquiterpenes. The three major compounds identified were germacrene-D (24.2%), (E)-caryophyllene (15.5%), and bicyclogermacrene (11.6%). The inner bark EO is composed mainly of sesquiterpenes hydrocarbons and the major components are alpha-copaene (14.9%) and alpha-(E)-bergamotene (13.0%). The outer bark EO is composed mainly of oxygenated sesquiterpenes and long-chain alkanes, and the major components are alpha-eudesmol (4.2%) and nonacosane (5.8%). The wood EO is mainly composed of long-chain alkanes and fatty acids, and the major components are nonacosane (9.7%) and palmitic acid (16.2%). The inner bark EO showed the strongest antimicrobial activity against the anaerobic bacteria Prevotella nigrescens (minimum inhibitory concentration-MIC of 50 µg mL−1). The outer bark and wood EOs showed MICs of 100 µg mL−1 for all aerobic microorganisms tested. The EOs presented low toxicity to Vero cells. These results suggest that K. coriacea, a Brazilian plant, provide initial evidence of a new and alternative source of substances with medicinal interest

Structural and Functional insights into the catalytic mechanism of the Type II NADH:quinone oxidoreductase family

Type II NADH:quinone oxidoreductases (NDH-2s) are membrane proteins involved in respiratory chains. These proteins contribute indirectly to the establishment of the transmembrane difference of electrochemical potential by catalyzing the reduction of quinone by oxidation of NAD(P)H. NDH-2s are widespread enzymes being present in the three domains of life. In this work, we explored the catalytic mechanism of NDH-2 by investigating the common elements of all NDH-2s, based on the rationale that conservation of such elements reflects their structural/functional importance. We observed conserved sequence motifs and structural elements among 1762 NDH-2s. We identified two proton pathways possibly involved in the protonation of the quinone. Our results led us to propose the first catalytic mechanism for NDH-2 family, in which a conserved glutamate residue, E(172) (in NDH-2 from Staphylococcus aureus) plays a key role in proton transfer to the quinone pocket. This catalytic mechanism may also be extended to the other members of the two-Dinucleotide Binding Domains Flavoprotein (tDBDF) superfamily, such as sulfide:quinone oxidoreductases

Desenvolvimento de um potenciostato de baixo custo para ser empregado em aulas experimentais de Eletroquímica / Development of a low cost potentiostat to be used in experimental classes of Electrochemistry

As atividades experimentais são apontadas como uma importante ferramenta para auxiliar na construção do conhecimento científico durante a formação discente. No entanto, muitas vezes, por falta de reagentes e equipamentos adequados, tais atividades são pouco exploradas nas escolas. Diante disso, este artigo relata a produção de um potenciostato de baixo custo realizada por alunos do curso Técnico Integrado em Mecatrônica do Instituto Federal de Santa Catarina (IFSC – Câmpus Criciúma). O potenciostato é um dispositivo que pode ser utilizado na determinação qualitativa e quantitativa de diferentes espécies químicas através da aplicação de potencial/corrente. Medidas de voltametria cíclica foram realizadas para testar o desempenho do protótipo desenvolvido. Os resultados obtidos apontaram que o potenciostato proposto pode ser satisfatoriamente utilizado em aulas experimentais de Eletroquímica. O custo final do protótipo foi de aproximadamente 230,00 reais, valor muito abaixo de um equipamento comercializado

Comportamento do Fluxo de co2 em dois Sítios Experimentais de Cultivo de Arroz

Comportamento do fluxo de CO 2 em dois sítiosexperimentais de cultivo de arro