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A G Hernández

Publications and source records attributed to A G Hernández.

14 recordsLinked to original sources
PubMed1990

Biochemical evidence of the antigenic cell surface heterogeneity of Leishmania mexicana.

In the present study, an enzymatical and structural analysis of Leishmania mexicana cell-surface components was carried out, demonstrating that protease and acid phosphatase activities were present at the L. mexicana cell surface. These findings correlate with the expression of the main components detected on the surface of L. mexicana promastigotes: the 50-kDa component is responsible for the acid phosphatase activity, whereas glycoprotein 65 (gp65) was characterized as the structural polypeptide of the surface protease. Furthermore, the 50- and 65-kDa antigens were found to be structurally different, inasmuch as no homology was observed in their peptide digestion profiles. The results presented in this communication confirm heterogeneity in the expression of the surface components of L. mexicana promastigotes at both the structural and the biochemical level.

Acid Phosphatase↗
PubMed1989

The heterogeneity of Leishmania cell-surface antigens.

A comparative study of the radioiodinated promastigote cell-surface antigens of Leishmania mexicana and L. major was carried out under reduced and nonreduced conditions by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by autoradiography. Under reduced conditions, the cell surface of L. mexicana promastigotes showed three iodinated polypeptides with molecular weights of 65,000, 50,000 and 27,000 daltons, whereas L. major promastigotes displayed a single polypeptide of 63,000 daltons. Under nonreduced conditions, the radioiodinated cell-surface component of L. major shifted to a mol.wt. of 51,000 daltons, whereas only one of the three components of L. mexicana (mol.wt., 65,000 daltons) underwent a large shift (to 59,000 daltons). The different immunochemical nature of the L. mexicana cell-surface antigens was demonstrated by using different anti-Leishmania sera. The rabbit anti-promastigote serum immunoprecipitated mainly the 50,000- and 27,000-dalton L. mexicana cell-surface polypeptides, whereas the rabbit anti-amastigote serum as well as a serum from a patient with cutaneous leishmaniasis immunoprecipitated almost exclusively the 65,000-dalton polypeptide. Immunoblot studies using a rabbit antibody against the L. major deglycosylated major surface antigen gp63 confirmed the differences in nature of the 65,000- and 50,000-dalton cell-surface antigens of L. mexicana. The results obtained are discussed in the light of the differences in antigenic cell-surface expression among Leishmania isolates and their consequences in the development of a differential diagnosis of leishmaniasis.

Animals↗
PubMed1986

The localization of a lectin-like component on the Leishmania cell surface.

The binding between macrophage-like cells J774G8 and Leishmania braziliensis (NR) promastigotes was studied 'in vitro' by a radioisotopic assay under various conditions in the absence of serum. Different sugars, N-acetyl-D-glucosamine, D-glucose, D-mannose, D-galactose, and chitin, diminished the binding of the parasite, whereas other sugars, D-arabinose, D-fucose and D-xylose, did not affect the binding. The presence of a lectin-like ligand specific for N-acetyl-D-glucosamine has been detected on the cell surface of the Leishmania braziliensis (NR) by fluorescence microscopy. These data suggest that the binding of the parasite to the host's cell is a ligand-receptor interaction which involves the participation of a lectin-like component on the parasite cell surface.

Animals↗
PubMed1985

Solubilization and partial purification of a cell surface component of Leishmania braziliensis.

A simple procedure that allowed the extraction and partial purification of a component of 65,000 mol.wt. from the surface of Leishmania braziliensis promastigotes is described. Iodinated cell surface membrane fractions were solubilized using Triton X-100 followed by Nonidet P-40. The macromolecular components were then freed of the detergents by passage of the extracts through a column of DE52 cellulose. The component of 65,000 mol.wt. was eluted from the column with 1 m NaCl. This component in whole parasites was immunoprecipitated by sera from patients with cutaneous, mucocutaneous, and diffuse cutaneous leishmaniasis and kala-azar. None of the major surface determinants reacted with sera from normal individuals with antibovine rabbit serum. The relevance and the possible applications on the immunoprophylaxis of the disease are briefly discussed.

Animals↗
PubMed1985

Leishmania braziliensis: cell surface differences in promastigotes of pathogenic and nonpathogenic strains.

A comparative study of cell surface characteristics of pathogenic and nonpathogenic promastigotes of Leishmania braziliensis, NR and LBY strains, respectively, was carried out by means of concanavalin A agglutination and labeling with concanavalin A-fluorescein isothiocyanate, concanavalin A-ferritin, and cationized ferritin. Cytochemical examination showed cell surface differences in lectin receptors and negative charge moieties in the two strains of L. braziliensis. The pathogenic NR strain agglutinated with low concentrations of concanavalin A and presented abundant lectin-binding and cationized ferritin-binding surface labeling. The nonpathogenic LBY strain neither agglutinated when incubated with concanavalin A, bound lectins, or cationized ferritin at the cell surface.

Agglutination↗
PubMed1983

Effect of a purified excreted factor from Leishmania brasiliensis on macrophage activity.

The effect of a purified glycoprotein excreted to the culture medium by Leishmania brasiliensis on the endocytic and degradative capacity of macrophages was studied. It was demonstrated that 125I-albumin incorporation as well as its intracellular fate by mouse peritoneal or tumor J774-G8 macrophages was greatly reduced when they were treated with excreted factor (EF). EF appears to alter also membrane properties in addition to its intracellular effect. The results are discussed in relation to the Leishmania survival mechanism inside the host macrophages and its pathogenicity.

Animals↗
PubMed1983

Leishmanial excreted factors and their possible biological role.

In the study of interactions between parasites of Leishmania species and their environment the release of a variety of materials has been detected. Some of these exo-metabolites are species-specific and may be exploited to characterize different leishmanial isolates. As the plasma membrane is the site of interaction between parasite and host it appears that the presence of metabolic products on, and their subsequent release from, the leishmanial cell surface bears a strong relationship to the biological performance of the parasite. The presence of a shedding mechanism in addition to other means of secretion has been shown in Leishmania braziliensis (NR strain). The products shed from the cell surface include glycoproteins and polysaccharide-like complexes. One of these glycoproteins has been purified, and it appears to affect macrophage activity. Because the recognition of these leishmanial metabolic products by antibody is mediated by the glycosylated portion of the secreted macromolecules, a limited repertoire of sugar residues may be common to these types of surface and extra-surface immunogens. Minor changes in the branching or sequence of sugars might constitute a code related to both serotype and biological activity of a given Leishmania strain.

Animals↗
PubMed1978

Protein synthesis by synaptosomes from rat brain: the effect of centrifugal forces.

1. Synaptosomal protein synthesis has been found to differ depending on whether synaptosomes are recovered from the sucrose gradients by centrifuging at 20,000 g or at 150,000 g. 2. The fraction obtained at 20,000 g incorporated 60% more amino acid into proteins after 30 min of incubation than the one obtained in the same period of time at 150,000 g. 3. The respiratory capacity of synaptosomes obtained at 20,000 g in the presence or absence of glucose as substrate, is also better preserved than that of those obtained at 150,000 g. 4. It is shown that the yield, enzymic content, and nucleic acid composition is the same in both fractions. 5. These results cannot be explained by the presence of inhibitory factors in the 150,000 g fraction or by the presence of better preserved free mitochondria in the 20,000 g fraction. 6. Our findings are best explained by postulating that the synaptosomal metabolic activity is damaged when synaptosomes are pelleted at too high a speed.

Acetylcholinesterase↗
PubMed1974

Protein synthesis by synaptosomes from rat brain. Contribution by the intraterminal mitochondria.

(1) The characteristics of protein synthesis in microsomal and synaptosomal fractions from rat brain were examined. A high sensitivity to ribonuclease and to cycloheximide, and the need for the presence of pH5 enzymes distinguished protein synthesis in microsomal fractions from protein synthesis in synaptosomes. (2) Under various conditions of incubation synaptosomal fractions prepared in sucrose showed limited protein synthesis compared with synaptosomal fractions prepared by using Ficoll. Such discrepancies could not be attributed to: (i) animal age, (ii) the metabolic state of the synaptosomal fraction, (iii) the absence of bivalent cations in the incubation medium or (iv) the temperature. (3) Protein synthesis in synaptosomal fractions was inhibited 50-65% by cycloheximide, 38-50% by chloramphenicol, 95% by puromycin, 70% by azide and 40% by deoxyglucose; ribonuclease had only a negligible inhibitory effect. (4) As a first approximation to the localization of the protein-synthetic machinery present in the synaptosomal fraction, the distribution of enzymes and radioactivity in subfractions of prelabelled synaptosomes was determined after osmotic shock with water. Approximately 60% of the total protein synthesis in the synaptosomal fraction occurred in the intraterminal mitochondria. (5) Protein synthesis in the intraterminal mitochondria did not show any fundamental difference from synthesis in somatic mitochondria, with respect to inhibition by cycloheximide and chloramphenicol. (6) It was concluded that if extramitochondrial protein synthesis occurs in synaptosomes, it must be very low.

Age Factors↗