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Biomedical subjects

M Medina

Publications and source records attributed to M Medina.

At least 55 records · Page 3Linked to original sources
PubMed2001

Hydrolysis of caseins and formation of hydrophilic and hydrophobic peptides by wild Lactococcus lactis strains isolated from raw ewes' milk cheese.

AIMS: To investigate the hydrolysis of alphaS1-, alphaS0-, betaB-, betaA1- and betaA2-caseins by 32 wild lactococci of different randomly amplified polymorphic DNA (RAPD) patterns, isolated from raw ewes' milk cheese, and the production of hydrophilic and hydrophobic peptides from whole casein by those strains. METHODS AND RESULTS: Most strains hydrolysed all caseins, and degraded beta-caseins to a larger extent than alphaS-caseins, when the proteolytic activity of whole cells was determined by capillary electrophoresis. Higher levels of hydrophilic than of hydrophobic peptides were produced from whole casein by all strains, according to reverse-phase high performance liquid chromatography analyses. CONCLUSIONS: Cell envelope proteinases of most lactococci isolated from raw ewes' milk cheese were CEPII, CEPII/III or CEPIII (classification of Exterkate et al. 1993). A negative correlation was found between degraded alphaS- and beta-caseins and a highly positive correlation between hydrophilic and hydrophobic peptides. SIGNIFICANCE AND IMPACT OF THE STUDY: Fast acid-producing lactococci from raw ewes' milk cheese have considerable and diverse caseinolytic activities. Their peptide production patterns do not reveal serious risks of bitter-flavour defect in cheeses if used as components of dairy starters.

Animals↗
PubMed2001

Roles of homocysteine in cell metabolism: old and new functions.

Mild hyperhomocysteinemia has been suggested as a new, independent risk factor for cardiovascular disease. This fact has produced a new, increased interest in the study of homocysteine metabolism and its relation to pathogenesis. This emergent area of biomedical research is reviewed here, stressing the biochemical and metabolic basis of the pathogenicity of increased levels of homocysteine.

Cardiovascular Diseases↗
PubMed2001

The effects of cultivating lactic starter cultures with bacteriocin-producing lactic acid bacteria.

The effects of bacteriocins produced by six strains of lactic acid bacteria on 9 mesophilic and 11 thermophilic commercial starter cultures were investigated in mixed cultures of commercial starters with bacteriocin-producing strains in milk. The bacteriocins produced by the test organisms were nisin A, nisin Z, lacticin 481, enterocin AS-48, a novel enterocin, and a novel plantaricin. Mesophilic commercial starters were in most cases tolerant of bacteriocins, with only two of the starters being partially inhibited, one by four and the other by two bacteriocins. The aminopeptidase activities of mesophilic starters were generally low, and only one of the combinations of mesophilic starter-bacteriocin producer gave double the aminopeptidase activity of the starter culture without the bacteriocin producer. Thermophilic commercial starters were more sensitive to bacteriocins than mesophilic starters, with six thermophilic starters being partially inhibited by at least one of the bacteriocins. Their aminopeptidase activities were generally higher than those of the mesophilic starters. The aminopeptidase activities of seven thermophilic starters were increased in the presence of bacteriocins, by factors of up to 9.0 as compared with the corresponding starter cultures alone. Bacteriocin-producing strains may be used as adjunct cultures to mesophilic starters for the inhibition of pathogens in soft and semihard cheeses, because mesophilic starters are rather tolerant of bacteriocins. Bacteriocin producers may also be used as adjunct cultures to thermophilic starters of high aminopeptidase activity, more sensitive to lysis by bacteriocins than mesophilic starters, for the acceleration of ripening in semihard and hard cheeses.

Aminopeptidases↗
PubMed2000

Presenilin affects arm/beta-catenin localization and function in Drosophila.

Presenilin is an essential gene for development that when disrupted leads to a neurogenic phenotype that closely resembles Notch loss of function in Drosophila. In humans, many naturally occurring mutations in Presenilin 1 or 2 cause early onset Alzheimer's disease. Both loss of expression and overexpression of Presenilin suggested a role for this protein in the localization of Armadillo/beta-catenin. In blastoderm stage Presenilin mutants, Arm is aberrantly distributed, often in Ubiquitin-immunoreactive cytoplasmic inclusions predominantly located basally in the cell. These inclusions were not observed in loss of function Notch mutants, suggesting that failure to process Notch is not the only consequence of the loss of Presenilin function. Human presenilin 1 expressed in Drosophila produces embryonic phenotypes resembling those associated with mutations in Armadillo and exhibited reduced Armadillo at the plasma membrane that is likely due to retention of Armadillo in a complex with Presenilin. The interaction between Armadillo/beta-catenin and Presenilin 1 requires a third protein which may be delta-catenin. Our results suggest that Presenilin may regulate the delivery of a multiprotein complex that regulates Armadillo trafficking between the adherens junction and the proteasome.

Animals↗
PubMed2000

Highly nonproductive complexes with Anabaena ferredoxin at low ionic strength are induced by nonconservative amino acid substitutions at Glu139 in Anabaena ferredoxin:NADP+ reductase.

Ferredoxin (Fd) and ferredoxin:NADP(+) reductase (FNR) from Anabaena function in photosynthetic electron transfer (et). The et interaction between the FNR charge-reversal mutant E139K and Fd at 12 mM ionic strength (mu) is extremely impaired relative to the reaction with wt FNR, and the dependency of k(obs) on E139K concentration shows strong upward curvature at protein concentrations > or = 10 microM. However, at values of mu > or = 200 mM, reaction rates approach those of wild-type FNR, and normal saturation kinetics are observed. For the E139Q mutant, which is also significantly impaired in its et interaction with Fd at low FNR concentrations and low mu values, the dependency of k(obs) on E139Q concentration shows a smaller degree of upward curvature at mu = 12 and 100 mM and shows saturation kinetics at higher values of mu. wt FNR and the E139D mutant both show a slight amount of upward curvature at FNR concentrations >30 microM at mu = 12 mM but show the expected saturation kinetics at higher values of mu. These results are explained by a mechanism in which the mutual orientation of the proteins in the complex formed at low ionic strength with the E139K mutant is so far from optimal that it is almost unreactive. At increased E139K concentrations, the added mutant FNR reacts via a collisional interaction with the reduced Fd present in the unreactive complex. The et reactivity of the low ionic strength complexes depends on the particular amino acid substitution, which via electrostatic interactions alters the specific geometry of the interface between the two proteins. The presence of a negative charge at position 139 of FNR allows the most optimal orientations for et at ionic strengths below 200 mM.

Amino Acid Substitution↗
PubMed2000

Serotonergic retinopetal projections from the dorsal raphe nucleus in the mouse demonstrated by combined [(3)H] 5-HT retrograde tracing and immunolabeling of endogenous 5-HT.

The present study demonstrated a direct serotonergic retinopetal projection in the mouse stemming from the lateral portion of the dorsal raphe nucleus bilaterally. A double-labeling technique was employed combining: (1) radioautography and retrograde axonal tracing following intraocular injection of [(3)H] 5-HT and (2) immunocytochemical identification of endogenous 5-HT. Radiolabeled neurons were only observed within the dorsal raphe nucleus and were always double-labeled with the 5-HT antibody. The radiolabeling appeared to be specific resulting from the retrograde transport of a radioactive 5-HT derivative product following uptake of the neurotransmitter by intraretinal terminals.

Animals↗
PubMed2000

delta-catenin is a nervous system-specific adherens junction protein which undergoes dynamic relocalization during development.

delta-catenin is a member of the Armadillo repeat family and component of the adherens junction discovered in a two-hybrid assay as a bona fide interactor with presenilin-1 (Zhou et al., [1997], NeuroReport 8:2085-2090), a protein which carries mutations that cause familial Alzheimer's disease. The expression pattern of delta-catenin was mapped between embryonic day 10 (E10) and adulthood by Northern blots, in situ hybridization and immunohistochemistry in the mouse. In development, delta-catenin is dynamically regulated with respect to its site of expression. It is first expressed within proliferating neuronal progenitor cells of the neuroepithelium, becomes down-regulated during neuronal migration, and is later reexpressed in the dendritic compartment of postmitotic neurons. In the mouse, delta-catenin mRNA is expressed by E10, increases and peaks at postnatal day (P)7, with lower levels in adulthood. In the developing neocortex, delta-catenin mRNA is strongly expressed in the proliferative ventricular zone and the developing cortical plate, yet is conspicuously less prominent in the intermediate zone, which contains migrating cortical neurons, delta-catenin protein forms a honeycomb pattern in the neuroepithelium by labeling the cell periphery in a typical adherens junction pattern. By E18, delta-catenin expression shifts primarily to nascent apical dendrites, a pattern that continues through adulthood. The dynamic relocalization of delta-catenin expression during development, taken together with previously published data which described a role for delta-catenin in cell motility (Lu et al., [1999] J. Cell. Biol. 144:519-532), suggests the hypothesis that delta-catenin regulation is closely linked to neuronal migration and may play a role in the establishment of mature dendritic relationships in the neuropil.

Animals↗
PubMed2000

Hemizygosity of delta-catenin (CTNND2) is associated with severe mental retardation in cri-du-chat syndrome.

Delta-catenin is an adherens junction protein involved in cell motility and expressed early in neuronal development. It was discovered as an interactor with presenilin-1. The genomic structure of the human delta-catenin gene (Human Gene Nomenclature Committee-approved symbol CTNND2) was determined and mapped to 5p15.2. A deletion of this chromosomal region has been associated with the cri-du-chat syndrome (CDCS), a segmental aneusomy syndrome of 5p that is associated with an unusual high-pitched cry at birth, facial dysmorphology, poor growth, and severe mental retardation. delta-catenin maps to a specific region in 5p15.2 that has been implicated in the mental retardation phenotype. The breakpoints in patients with 5p terminal deletions were characterized with respect to the severity of mental retardation and the physical location of the delta-catenin gene. A strong correlation was found between the hemizygous loss of delta-catenin and severe mental retardation. These findings and the properties of delta-catenin as a neuronal-specific protein, expressed early in development and involved in cell motility, support its role in the mental retardation of CDCS when present in only one copy.

Armadillo Domain Proteins↗
PubMed2000

Structural basis of the catalytic role of Glu301 in Anabaena PCC 7119 ferredoxin-NADP+ reductase revealed by x-ray crystallography.

The three-dimensional crystal structure of the Glu301Ala site-directed mutant of ferredoxin-NADP+ reductase from Anabaena PCC 7119 has been determined at 1.8A resolution by x-ray diffraction. The overall folding of the Glu301Ala FNR mutant shows no significant differences with respect to that of the wild-type enzyme. However, interesting conformational changes are detected in the side chain of another glutamate residue, Glu139, which now points towards the FAD cofactor in the active center cavity. The new conformation of the Glu139 side chain is stabilized by a network of five hydrogen bonds to several water molecules, which seem to hold the carboxylate side chain in a rather fixed position. This interacting network connects the Glu139 side chain to the Ser80 side chain through a series of three water molecules. These observations are discussed in terms of the reactivity of Glu301Ala ferredoxin-NADP+ reductase towards its substrates, and the role of Glu301 in the catalysis is re-examined. Moreover, a structural explanation of the different reoxidation properties of this mutant is given on the basis of the reported structure by modeling the hypothetical flavin C(4a)-hydroperoxide intermediate. The model shows that the distal oxygen of the peroxide anion could be in an appropriate situation to act as the proton donor in the reoxidation process.

Anabaena↗
PubMed2000

Molecular systematics of the order anaspidea based on mitochondrial DNA sequence (12S, 16S, and COI).

Fragments from three mitochondrial genes (12S, 16S, and COI) were sequenced to reconstruct a molecular phylogeny of the opisthobranch order Anaspidea. The molecular phylogeny supports the placement of the genus Akera, a taxon previously regarded by some authors as a cephalaspidean, within the Anaspidea. Incongruence between the molecular data and the classifications based on morphology suggests that some of the taxonomic characters (i.e., shell, parapodia fusion) traditionally used for the classification of sea hares must be reevaluated, since they may be homoplastic. The ancestral nature of Notarchus based on the molecular evidence suggests that homoplasy may be an explanation for the morphological resemblance of this species to the more derived sea hares with highly fused parapodia and concentrated nerve ganglia. Finally, examples are given of how comparative studies of the evolution of learning mechanisms in the anaspidean clade will benefit from the phylogenetic hypothesis presented in this paper.

Animals↗
PubMed2000

Indium-111 labelled white blood cell scintigraphy in cranial and spinal septic lesions.

Cranial and spinal infections are severe events that require timely diagnosis and treatment. Physical and neurological examination, laboratory tests and radiological imaging may be insufficient for assessing cranial and spinal septic lesions. This study aimed to evaluate the accuracy of indium-111 white blood cell (WBC) scan in assessing the presence of leucocytes in intracranial and spinal lesions, and in the diagnosis, management and follow-up of primary, post-traumatic and post-surgical infections. One hundred and twenty-four subjects were included in the study (48 with post-traumatic or post-surgical lesions, 73 with primary cerebral lesions, and 3 with spinal lesions). All patients underwent a diagnostic work-up including planar scans with 111In-labelled WBCs, at 4 and 24 h post tracer injection. All subjects underwent surgical treatment. Patients who did not recover from the infection as suggested by clinical evolution underwent further treatment (up to three times) and further WBC scans (up to four times). WBC scintigraphy correctly identified all the areas of leucocyte accumulation, as confirmed after surgery. WBC scintigraphy also correctly excluded the presence of leucocytes in all other lesions, as demonstrated at surgery. The results of this study confirm the accuracy of WBC scan for the assessment of patients with cranial and spinal lesions, in whom the demonstration of leucocyte accumulation can ease the diagnosis of infection, and indicate that the method is also accurate for the follow-up and management of neurosurgical patients.

Adult↗
PubMed2000

Demonstration of McCune-Albright mutations in the liver of children with high gammaGT progressive cholestasis.

Two patients presented with neonatal cholestasis and acholic stools as first manifestations of McCune-Albright syndrome. Both went through an extensive evaluation including an exploratory laparotomy with peroperative cholangiography which ruled out biliary atresia. One patient presented from the fourth month of life with the classical café-au-lait spots following Blaschko's lines, while less classical café-au-lait spots were seen in the second patient at the age of 4 years. Bone lesions were seen in one patient at the age of 2.5 years and in the other at the age of 4 years. Despite the severity of presentation, both patients cleared their jaundice within 6 months, but still had mild abnormalities of liver function tests. Both patients showed an activating mutation of codon 201 in the gene encoding the alpha-subunit of the G-protein that stimulates adenylcyclase in liver tissue, suggesting that this metabolic defect could be responsible for the cholestatic syndrome. Similar mutations have been found in other affected tissues in patients with the McCune-Albright syndrome. We propose that McCune-Albright syndrome be included in the list for differential diagnosis of neonatal cholestasis and chronic cholestasis of infancy, as a rare cause.

Arginine↗
PubMed2000

Enhancement of hydralazine hypotension by low doses of isoniazid. Possible role of semicarbazide-sensitive amine oxidase inhibition.

The influence of pretreatment with 1 through 300 mg/kg ip of isoniazid (ISO) on blood pressure and heart rate responses to 0.1 mg/kg iv of hydralazine (HYD) was assessed in rats anesthetized with chloralose--urethane. HYD hypotension was significantly enhanced by ISO at doses between 3 and 300 mg/kg ip. Heart rate was not influenced by HYD in control or pretreated animals. Depressor responses to 0.2 mg/kg iv of pinacidil (PIN) were also potentiated by ISO at 100 and 300, but not at 30 mg/kg. Similarly, ISO decreased cerebral gamma-aminobutyric acid (GABA) at the two highest doses; 30 mg/kg was without effect. Pretreatment of rats with ISO at 1 through 300 mg/kg failed to influence HYD-induced relaxation of aortic rings. These results were interpreted as indicating that potentiation of HYD hypotension by high doses of ISO is not specific for that vasodilator and is related to decreased cerebral GABA, as postulated previously. Lower doses could specifically potentiate the HYD-induced hypotensive effect by inhibition of semicarbazide-sensitive amine oxidase (SSAO), since both ISO and HYD are potent inhibitors of this enzyme. In support of this hypothesis, the SSAO inhibitors, benserazide (100 mg/kg ip) and mexiletine (50 mg/kg ip), were also found to enhance HYD hypotension.

Amine Oxidase (Copper-Containing)↗
PubMed2000

Phenolic compounds and browning in sherry wines subjected to oxidative and biological aging.

The composition in hydroxybenzoic and hydroxycinnamic acids, hydroxycinnamic esters, tyrosol, syringaldehyde, and flavan-3-ol derivatives of three different types of sherry wine obtained by aging of the same starting wine under different conditions was studied. So-called "fino" wine was obtained by biological aging under flor yeasts, "oloroso" wine by oxidative aging, and "amontillado" wine by a first stage of biological aging followed by a second oxidative step. On the basis of the results, the wines subjected to oxidative aging exhibited higher phenol contents, in addition to scarcely polar compounds absorbing at 420 nm that were absent in the wines obtained by biological aging. Taking into account that flavan-3-ol derivatives play an important role in wine browning, a model catechin solution was inoculated with flor yeast which, contrary to the findings of other authors in the absence of yeasts, formed no colored compounds. This different behavior may account for the resistance to browning of pale sherry wines in the presence of flor yeasts.

Food Handling↗
PubMed2000

A redox-dependent interaction between two electron-transfer partners involved in photosynthesis.

Ferredoxin:NADP+:reductase (FNR) catalyzes one terminal step of the conversion of light energy into chemical energy during photosynthesis. FNR uses two high energy electrons photoproduced by photosystem I (PSI) and conveyed, one by one, by a ferredoxin (Fd), to reduce NADP+ to NADPH. The reducing power of NADPH is finally involved in carbon assimilation. The interaction between oxidized FNR and Fd was studied by crystallography at 2.4 A resolution leading to a three-dimensional picture of an Fd-FNR biologically relevant complex. This complex suggests that FNR and Fd specifically interact prior to each electron transfer and disassemble upon a redox-linked conformational change of the Fd.

Anabaena↗
PubMed2000

Molecular characterization of a urea transporter in the gill of the gulf toadfish (Opsanus beta).

Urea excretion by the gulf toadfish (Opsanus beta) has been shown in previous studies to be a highly pulsatile facilitated transport, with excretion probably occurring at the gill. The present study reports the isolation of an 1800 base pair (kb) cDNA from toadfish gill with one open reading frame putatively encoding a 475-residue protein, the toadfish urea transporter (tUT). tUT, the first teleostean urea transporter cloned, has high homology with UTs (facilitated urea transporters) cloned from mammals, an amphibian and a shark, and most closely resembles the UT-A subfamily. When expressed in Xenopus laevis oocytes, tUT increased urea permeability (as measured by [(14)C]urea uptake) five- to sevenfold, and this permeability increase was abolished by phloretin, a common inhibitor of other UTs. Northern analysis using the 1.8 kb clone was performed to determine the tissue distribution and dynamics of tUT mRNA expression. Of six tissues examined (gill, liver, red blood cells, kidney, skin and intestine), only gill showed expression of tUT mRNA, with a predominant band at 1.8 kb and a minor band at 3.5 kb. During several points in the urea pulse cycle of toadfish (0, 4, 6, 12 and 18 h post-pulse), measured by excretion of [(14)C]urea into the water, gill mRNA samples were obtained. Expression of tUT mRNA was found to be largely invariant relative to expression of beta-actin mRNA over the pulse cycle. These results further confirm the gill localization of urea transport in the toadfish and suggest that tUT regulation (and the regulation of pulsatile urea excretion) is probably not at the level of mRNA control. The results are discussed in the context of the mechanisms of vasopressin-regulated UT-A in mammalian kidney and morphological data for the toadfish gill.

Amino Acid Sequence↗
PubMed2000

Stromal tumors of the stomach. Review of our experience and reclassification of a series of patients.

OBJECTIVE: To retrospectively review a series of 12 patients operated on in our department for stromal tumor of the stomach. Clinical and morphological data, and the patients' postoperative course, were analyzed. METHODS: Medical records for 12 patients (mean age 63.3 years) were retrospectively reviewed to obtain data on clinical presentation, diagnosis and treatment. Surgical morbidity and mortality were analyzed. A pathologist reviewed the resected specimens to determine the morphological factors of prognostic value. The biological nature of the tumor was reclassified based exclusively on mitotic index, and all tumors were staged according to the TGM system. Recurrence and survival rates were also calculated. RESULTS: The most frequent clinical presentation was abdominal pain and gastrointestinal bleeding. The most sensitive diagnostic methods were computerized tomography and echographic endoscopy. Operability and resectability rates were 100% and 91.6% respectively. Local resection was done in 5 patients, partial gastrectomy in 5, and extended total gastrectomy in 1. Histologically, 6 cases were muscular tumors (2 leiomyomas, 3 low-grade leiomyosarcomas and 1 high-grade leiomyosarcoma), 2 were gastrointestinal autonomic nerve (GAN) tumors, and 4 were pure stomal tumors. The morbidity rate was 33.3% and the mortality rate was 8.3% (1 patient). All patients were followed up: 1 patient each died after 9 months and 4 years, 1 developed liver metastases after a disease-free interval of 14 months, and the other 9 patients were still alive and free of disease after intervals ranging from 4 months to 7 years. CONCLUSIONS: Stromal tumors include a group of tumors which may present muscular differentiation (the most frequent type), neural differentiation (GAN tumors) or no differentiation at all (pure stromal tumors). The mitotic index is the most valid parameter to determine biological nature, considering that classification as a benign tumor requires the total absence of mitoses. Treatment was mostly surgical, and local resection with adequate safety margins was effective. Prognosis was relatively good, but long-term follow-up is needed to assess the malignant potential of these tumors.

Adult↗