ABSTRACT
Most aerobic organisms are exposed to oxidative stress. Looking for enzyme activities involved in the bacterial response to this kind of stress, we focused on the btuE-encoded Escherichia coli BtuE, an enzyme that shares homology with the glutathione peroxidase (GPX) family. This work deals with the purification and characterization of the btuE gene product. Purified BtuE decomposes in vitro hydrogen peroxide in a glutathione-dependent manner. BtuE also utilizes preferentially thioredoxin A to decompose hydrogen peroxide as well as cumene-, tert-butyl-, and linoleic acid hydroperoxides, confirming that its active site confers non-specific peroxidase activity. These data suggest that the enzyme may have one or more organic hydroperoxide as its physiological substrate. The btuE gene was induced when cells were exposed to oxidative stress elicitors that included potassium tellurite, menadione and hydrogen peroxide, among others, suggesting that BtuE could participate in the E. coli response to reactive oxygen species. To our knowledge, this is the first report describing a glutathione peroxidase in E. coli.
Subject(s)
Escherichia coli Proteins/metabolism , Escherichia coli/enzymology , Glutathione Peroxidase/metabolism , Oxidative Stress , Periplasmic Binding Proteins/metabolism , Escherichia coli/genetics , Escherichia coli Proteins/chemistry , Escherichia coli Proteins/genetics , Glutathione/chemistry , Glutathione/metabolism , Glutathione Peroxidase/chemistry , Glutathione Peroxidase/genetics , Hydrogen Peroxide/chemistry , Hydrogen Peroxide/metabolism , Periplasmic Binding Proteins/chemistry , Periplasmic Binding Proteins/geneticsABSTRACT
Potassium tellurite (K(2)TeO(3)) is harmful to most organisms and specific mechanisms explaining its toxicity are not well known to date. We previously reported that the lpdA gene product of the tellurite-resistant environmental isolate Aeromonas caviae ST is involved in the reduction of tellurite to elemental tellurium. In this work, we show that expression of A. caviae ST aceE, aceF, and lpdA genes, encoding pyruvate dehydrogenase, dihydrolipoamide transacetylase, and dihydrolipoamide dehydrogenase, respectively, results in tellurite resistance and decreased levels of tellurite-induced superoxide in Escherichia coli. In addition to oxidative damage resulting from tellurite exposure, a metabolic disorder would be simultaneously established in which the pyruvate dehydrogenase complex would represent an intracellular tellurite target. These results allow us to widen our vision regarding the molecular mechanisms involved in bacterial tellurite resistance by correlating tellurite toxicity and key enzymes of aerobic metabolism.
Subject(s)
Aeromonas/enzymology , Drug Resistance, Bacterial/genetics , Pyruvate Dehydrogenase Complex/metabolism , Tellurium/toxicity , Aeromonas/genetics , Escherichia coli/drug effects , Escherichia coli/genetics , Pyruvate Dehydrogenase Complex/geneticsABSTRACT
Potassium tellurite (K(2)TeO(3)) is extremely toxic for most forms of life and only a limited number of organisms are naturally resistant to the toxic effects of this compound. Crude extracts prepared from the environmental isolate Aeromonas caviae ST catalize the in vitro reduction of TeO32- in a NADH-dependent reaction. Upon fractionation by ionic exchange column chromatography three major polypeptides identified as the E1, E2, and E3 components of the pyruvate dehydrogenase (PDH) complex were identified in fractions exhibiting tellurite-reducing activity. Tellurite reductase and pyruvate dehydrogenase activities co-eluted from a Sephadex gel filtration column. To determine which component(s) of the PDH complex has tellurite reductase activity, the A. caviae ST structural genes encoding for E1 (aceE), E2 (aceF), and E3 (lpdA) were independently cloned and expressed in Escherichia coli and their gene products purified. Results indicated that tellurite reductase activity lies almost exclusively in the E3 component, dihydrolipoamide dehydrogenase. The E3 component of the PDH complex from E. coli, Zymomonas mobilis, Streptococcus pneumoniae, and Geobacillus stearothermophilus also showed NADH-dependent tellurite reductase in vitro suggesting that this enzymatic activity is widely distributed among microorganisms.
Subject(s)
Aeromonas/enzymology , Bacterial Proteins/metabolism , Dihydrolipoamide Dehydrogenase/metabolism , Oxidoreductases/metabolism , Tellurium/metabolism , Aeromonas/drug effects , Aeromonas/genetics , Cloning, Molecular , Dihydrolipoamide Dehydrogenase/genetics , Escherichia coli/enzymology , Escherichia coli/genetics , Oxidation-Reduction , Oxidoreductases/chemistry , Tellurium/toxicityABSTRACT
Se revisaron algunos aspectos cardiovasculares relacionados con la hipertensión arterial presente en pacientes diabéticos, hospitalizados en el Hospital "José G. Hernández". I.V.S.S. Caracas. Desde hace muchos años se conoce la especial tendencia que tienen los diabéticos para presentar enfermedades vasculares y ésto ha sido documentado en numerosos estudió epidemiológicos, clínicos y anatomo-patológicos. Pero el papel de la hipertensión en diabéticos no ha sido todavía claramente definido, ni bien conocido. Nuestro estudio demuestra una incidencia de hipertensión en diabéticos hospitalizados de 40,5%. 125 casos (83,3%) tenían DM tipo II (DM estable del adulto) y 25 casos (16,7%) tenían DM tipo I (DM tipo juvenil). El diagnóstico de cardiopatía isquémica e hipertensiva se hizo en 128 casos (85,3%). Em 38 casos (25,3%) encontramos insuficiencia cardíaca congestiva. En 25 casos (16,6%) hallazgos electrocardiográficos de infarto miocárdico antiguo no reconocidos previamente ("silentes"). Se encontró nefropatía diabética en 31 casos (20,6%) y fue la responsable de los casos de H. A. Secundaria. En 119 casos (79,3%) encontramos hipertensión "esencial". El porcentaje de mortalidad fue del 12%