Search PubMed⌕ Search

Biomedical subjects

D M Esquivel

Publications and source records attributed to D M Esquivel.

7 recordsLinked to original sources
PubMed2000

Electron paramagnetic resonance study of the migratory ant Pachycondyla marginata abdomens.

Electron paramagnetic resonance was used to investigate the magnetic material present in abdomens of Pachycondyla marginata ants. A g congruent with 4.3 resonance of high-spin ferric ions and a very narrow g congruent with 2 line are observed. Two principal resonance broad lines, one with g > 4.5 (LF) and the other in the region of g congruent with 2 (HF), were associated with the biomineralization process. The resonance field shift between these two lines, HF and LF, associated with magnetic nanoparticles indicates the presence of cluster structures containing on average three single units of magnetite-based nanoparticles. Analysis of the temperature dependence of the HF resonance linewidths supports the model picture of isolated magnetite nanostructures of approximately 13 nm in diameter with a magnetic energy of 544 K. These particles are shown to present a superparamagnetic behavior at room temperature. The use of these superparamagnetic particle properties for the magnetoreception process of the ants is suggested.

Animals↗
PubMed1998

Phylogenetic affiliation and ultrastructure of uncultured magnetic bacteria with unusually large magnetosomes.

Natural enrichments of magnetic bacteria from the Itaipu lagoon near Rio de Janeiro were dominated by coccoid-to-ovoid morphotypes that produced unusually large magnetosomes. To determine the phylogenetic position of these unusual microorganisms, 16S rRNA genes were retrieved from bacteria magnetically separated from sediment of the Itaipu lagoon by in vitro amplification and cloning of PCR products into a plasmid vector. Partial sequencing of the obtained clones revealed two clusters of closely related sequences affiliated to a distinct lineage consisting exclusively of magnetic bacteria within the alpha-subclass of Proteobacteria. For a detailed phylogenetic analysis, several almost complete sequences of the 16S rRNA genes were determined. One representative clone of each cluster provided a PCR template for the in vitro transcription of group-specific polynucleotide probes complementary to a variable region of the 16S rRNA molecule. At least three different morphotypes of magnetic bacteria were reliably identified by post-embedding hybridization of ultra-thin sections. Electron microscopic analyses of hybridized cells enabled for the first time a detailed description of the morphological variety and ultrastructure of phylogenetically identified, uncultured magnetic bacteria. Two distinct coccoid bacteria were identified by the transcript probe complementary to the 16S rRNA sequence mabrj12, whereas the probe complementary to the sequence mabrj58 allowed the identification of an ovoid morphotype that displayed magnetosomes with the largest volumes observed to date.

Bacteria↗
PubMed1990

Magnetotaxis.

The ability of magnetotactic bacteria to orientate and navigate along geomagnetic lines is due to intracellular magnetic particles. These are enclosed within a membrane to form a magnetosome, a specialized organelle of magnetotactic organisms. The magnetic crystallite of many of the magnetotactic bacteria and algae is the iron oxide magnetite (Fe3O4) but recently a multicellular bacterial aggregate has been found to contain magnetic iron sulphide. Magnetotactic bacteria are found in regions of low oxygen pressure. Those of the Northern hemisphere are north-seeking while those of the Southern hemisphere are south-seeking. The opposite polarity of their internal magnets enables both types to travel to the deeper, less oxygenated, regions of their aqueous environments.

Bacterial Physiological Phenomena↗
PubMed1978

Generation of free radicals from phenazine methosulfate in Trypanosoma cruzi epimastigotes.

A significant growth inhibition of Trypanosoma cruzi epimastigotes by phenazine methosulfate (PMS) was observed in Warren's medium. This toxic activity could be related to the following parameters: a) formation of phenazinium free radical, b) generation of superoxide anion in intact cells incubated with PMS, and c) PMS also increased significantly the rate of O2- generation in epimastigotes mitochondrial and microsomal fractions using NADH as electron donor.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

Hydrogen bond indices and tertiary structure of yeast tRNAPhe.

The rigidity and stability of the tertiary structure of yeast tRNAPhe is related to a bond index obtained in an IEHT (iterative extended Hückel theory) calculation. The index permits a quantitative estimate of the electron density along the hydrogen bond, having thus an appealing physical meaning. The results indicate that Hoogsteen-type bonds have, as expected, greater electronic population than Watson-Crick type ones. Other non-Watson-Crick pairs, the wobble pair and G15-C48, exhibit high values of the index for the NH...O bond. In the triples, the electron density of the hydrogen bridges does not weaken (compared with the one of the pairs involved). Contour density maps are shown and dipolar moments of pairs and triples are qualitatively discussed.

Anticodon↗