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Biomedical subjects

M E Fernández

Publications and source records attributed to M E Fernández.

At least 19 recordsLinked to original sources
PubMed2006

Algorithms for dairy barn design: resting, feeding, and exercise.

This study presents a series of algorithms designed to assist farmers and other decision-makers in the design of dairy cattle housing. Four algorithms have been developed, each for a different basic design (2 rows head-to-head, 2 rows head-to-wall, 3 rows, or rows perpendicular to feed alley). Each algorithm requires input of herd size and various other parameters (e.g., free-stall width), depending on the design; the output gives barn layout and overall size, thus facilitating comparison of designs in terms of financial cost and animal welfare. Although these algorithms have been developed primarily for small family farms in Galicia (northwest Spain) with herd sizes of up to 250, they could be useful for herds of any size, because herd size is an input parameter. We consider that these algorithms are useful tools for dairy farm planning, and they can be readily incorporated into personal computer applications, greatly facilitating their application.

Algorithms↗
PubMed2004

TEM and molecular simulation studies on the hydroxylapatite structure with Si and Mg impurities.

Transmission electron microscopy (TEM) and molecular simulation studies of traces of chemical elements such as Mg, Si, and OH in the hydroxylapatite (CaHAP) crystal structure obtained from the sand dollar were carried out. Two different types of CaHAP crystal morphologies in the samples synthesized by the hydrothermal method used were observed. Reflections with regular intensity in the experimental electron diffraction patterns obtained from these morphologies were observed. However, when these results were compared with a simulated electron diffraction pattern (which was obtained using the crystalline structure proposed for the hydroxylapatite) some forbidden reflections in the experimental pattern were observed. Then, in order to reproduce the experimental patterns Si and Mg atoms in the crystalline lattice were introduced. These elements in the elemental chemical analysis carried out by X-ray energy dispersive spectroscopy (EDS) in the typical CaHAP morphologies were detected. The positions of these atoms in the asymmetric unit were obtained using molecular simulation and during the relaxation process, the structure did not show changes in the lattice parameters. Subsequently, the crystalline structure was reproduced and matched the electron diffraction patterns simulated resulting in the experimental electron diffraction pattern. Experimental and simulated X-ray diffraction spectra were also matched.

Biocompatible Materials↗
PubMed2003

New model for the hydroxyapatite-octacalcium phosphate interface.

Some experimental results have indicated that hydroxyapatite (HA) and octacalcium phosphate (OCP) can form an epitaxic interface. Subsequently the OCP-HA interface has become of great biological interest in the context of mineralized tissue formation. In this work a new OCP-HA interface model based on Brown's proposed configuration [Brown (1962), Nature, 197, 1048-1050] and using the minimum interface free-energy optimization is presented. This new model is formed by half a unit cell of HA and one unit cell of OCP, as in Brown's model, but in our case [1-210] of HA is 'glued' with [010] of OCP. Therefore, the relationship found was: [000-1](HA) parallel to [001](OCP) and [1-210](HA) parallel to [010](OCP). Self-consistent field methods were used for the analysis of Brown's model and ours. It is shown that the atoms in our model have similar environments as in the HA and OCP unit cells and that, as a result of the differences between HA and OCP unit-cell parameters, this interface presents misfit-dislocation-like features. High-resolution transmission electron microscopy (HREM) simulated images for the new interface model have been included and, when they are compared with the experimental ones, the similarity is quite good.

Journal Article↗
PubMed2000

Cadmium inhibition of a structural wheat peroxidase.

The major peroxidase from 15-day-old wheat plants was purified to homogeneity by FPLC ion exchange and molecular exclusion chromatography. It consists of a single polypeptide of M(r) 37,500 according to gel filtration and SDS-PAGE and has a pI of 7.0. Kinetics of pyrogallol peroxidation showed that the enzyme follows the accepted mechanism for peroxidase, with kinetic constants k(1) =4.4x10(6) M(-1) s(-1) and k(3) =8.6x10(5) M(-1) s(-1). The effect of different metal ions was assayed on peroxidase activity. None of the ions used had any effect on enzyme activity, except for Cd(II), which was an inhibitor. This was an unexpected and novel finding for a peroxidase. The kinetics of pyrogallol peroxidation at different concentrations of Cd(II) have been studied and a mechanism for Cd(II) inhibition proposed. The results obtained could explain, in part, cadmium-induced oxidative stress.

Cadmium↗
PubMed1998

Evidence for an unusual electronic structure of wheat germ peroxidase compound I.

Oxidized states of wheat germ peroxidase isozyme C2 (WGP C2) were investigated by means of electronic absorption spectroscopy. Addition of one molar equivalent of H2O2 to ferric WGP C2 led to the formation of an oxidized species with an absorption spectrum very similar to that of peroxidase compound II, with a Soret maximum at 411 nm and visible maxima at 523 and 553 nm. The transformation took place with an isosbestic point at 409 nm. Stopped flow spectroscopy showed no inflection points for the formation of this species when it was registered at 420 nm, and we could verify the persistence of the isosbestic point from 20 ms to 10 s. The oxidized species decays spontaneously to ferric enzyme in a double-exponential manner. By adding excess H2O2 to the system we obtained an inactive derivative identical to horseradish peroxidase P-670. In the presence of one equivalent of reducing substrate and excess H2O2 compound III was formed. The results so indicate that the species obtained in the reaction of WGP C2 with equimolecular amounts of H2O2 is compound I. The resulting compound I spectrum was identical to that of cytochrome c peroxidase, suggesting the formation of a protein radical rather than the typical pi cation radical, a feature which had not been described before for a plant peroxidase.

Enzyme Activation↗
PubMed1996

Ca2+ activation of wheat peroxidase: a possible physiological mechanism of control.

Peroxidation of substrates such as ascorbic acid, pyrogallol, or ferulic acid, as well as indole acetic acid oxidation catalyzed by wheat germ peroxidase (WGP)2 C2, were found to be activated by Ca2+. This activation is independent of the stabilizing effect of structural Ca2+ reported for peroxidases. Steady state kinetics of ferulic acid oxidation catalyzed by WGP C2 showed an increase in the rate of compound I formation and of compound II decomposition in the presence of the ion, evidenced as an increase in rate constants k1, from 8.9 x 10(5) to 4.5 x 10(5) M-1 cm-1, and k3, from 4.4 x 10(5) to 1.1 x 10(6) M-1 cm-1. The dissociation constant Kd, for the cyanide derivative of the enzyme showed a marked decrease from 220 to 34 microM in the presence of Ca2+, thus implying an effect of the ion in the H2O2 binding step. In the presence of Ca2+, a conformational change in the protein was revealed by tryptophan fluorescence, providing a basis for the activation mechanism. Other peroxidases such as horseradish peroxidase and WGP C3 were not activated by Ca2+. The results suggest the existence of a physiological mechanism of control of peroxidase isozymes activity mediated by Ca2+.

Calcium↗
PubMed1991

[Prevalence of the Epstein-Barr virus among different populations in the central area].

In order to estimate the seroprevalence of the Epstein-Barr virus in the centre area, a serological study is carried out using the indirect immunofluorescence technique on 759 supposed healthy people, from both sexes and with ages between 6 months and 50 years, 565 from which were living in urban areas (Madrid and Guadalajara city) and 194 in rural areas (Arganda del Rey, Madrid) and Chiloeches (Guadalajara). Global seroprevalence was of 81% in Madrid city, 90% in Guadalajara city and 85% in both rural populations. Comparing groups of the same age, we have not found any statistically significant differences between the urban (86%) and the rural (85%) areas. Neither we have found any relation between seropositivity and sex (74.7% for women and 81% for men). On the other hand, we observed that in our study group, seroprevalence was related to socioeconomic status--the higher the antibody percentages, the lower the socioeconomic status, both in the rural and in the urban areas (p less than 0.001)-- and age antibody percentages increased with age, with p less than 0.025 for urban areas and p less than 0.05 for rural areas.

Adolescent↗
PubMedDate not supplied

Effect of salicylate poisoning on insulin secretion. Studies on its mechanism of action.

Sodium salicylate poisoning increased glucose-induced insulin secretion by slices of rat pancreas. The alpha adrenergic blocker phentolamine, but not salicylate poisoning, overcame the inhibitory effect of epinephrine on insulin secretion. Theophylline (5, 10 and 15 mM) significantly increased the insulin secretion induced by 11 mM glucose. The highest insulin response was obtained when theophylline was used at a 10 mM concentration. However, when pancreas slices from salicylate poisoned rats were used, a 5 mM concentration was sufficient to achieve maximal insulin response. Salicylate poisoning diminished the free tubulin pool, an action that was impaired by imidazole; however, imidazole did not modify the effect of the ionophore A23187. The results suggest that: a) sodium salicylate poisoning increases B-cell response to glucose; b) changes in alpha adrenergic activity are not related to the mechanism of action of salicylate; c) an increment in the cAMP concentration may mediate the stimulatory effect of salicylate poisoning on insulin secretion; d) the effect of salicylate on the microtubular system is indirect and probably mediated through an increment in pancreatic cAMP.

Animals↗