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R López

Publications and source records attributed to R López.

At least 19 recordsLinked to original sources
PubMed1992

Structural analysis and biological significance of the cell wall lytic enzymes of Streptococcus pneumoniae and its bacteriophage.

The development of an appropriate technique for the identification of autolysin-defective mutants of pneumococcus has been a fundamental step to carry out studies on the molecular characteristics of the lytic enzymes of Streptococcus pneumoniae and its bacteriophage. Our results show that the principal pneumococcal autolysin (an amidase) is responsible for the separation of the daughter cells at the end of the cell division. On the other hand, this system provides a reliable experimental model to support the extended idea concerning the modular organization of most proteins. The comparative analyses of the deduced amino acid sequences of these enzymes, as well as the construction of functional chimeric phage-bacterial enzymes, demonstrate that the C-terminal domain, which contains a large number of repeated amino acid motifs, is the substrate-binding domain, whereas the N-terminal domain provides enzymatic specificity. We propose that the pneumococcal lytic enzymes have evolved by modular exchange providing examples of the types of novel genes that the bacteria or the phage might create to allow them to become adapted to new environmental situations.

Amino Acid Sequence↗
PubMed1992

Effects of omeprazole, ranitidine, famotidine and placebo on gastric secretion in patients undergoing elective surgery.

We have compared the effects of omeprazole, ranitidine, famotidine and placebo on gastric secretion in a double-blind study in 110 patients undergoing elective surgery. Three hours before operation, the patients received, orally, omeprazole 40 mg, ranitidine 150 mg, famotidine 40 mg or placebo. Gastric volume and pH were measured immediately after induction of anaesthesia. Omeprazole, ranitidine and famotidine produced a significant increase in gastric pH and a significant decrease in gastric volume compared with placebo. When the effects of omeprazole on gastric volume were compared with those of ranitidine and famotidine, no significant difference was found, but omeprazole was significantly less effective in increasing gastric pH. The number of patients having a pH less than 2.5 and a volume greater than 0.4 ml kg-1 were: none in the ranitidine group, one (3%) in the famotidine group, four (15%) in the omeprazole group and six (23%) in the placebo group. We conclude that omeprazole 40 mg given 2-4 h before surgery does not afford adequate prophylaxis for the acid aspiration syndrome.

Adolescent↗
PubMed1992

Role of the major pneumococcal autolysin in the atypical response of a clinical isolate of Streptococcus pneumoniae.

The autolytic enzyme (an N-acetylmuramyl-L-alanine amidase) of a clinical isolate, strain 101/87, which is classified as an atypical pneumococcus, has been studied for the first time. The lytA101 gene coding for this amidase (LYTA101) has been cloned, sequenced, and expressed in Escherichia coli. The LYTA101 amidase has been purified and shown to be similar to the main autolytic enzyme (LYTA) present in the wild-type strain of Streptococcus pneumoniae, although it exhibits a lower specific activity, a higher sensitivity to inhibition by free choline, and a modified thermosensitivity with respect to LYTA. Most important, in contrast with the LYTA amidase, the activity of the LYTA101 amidase was inhibited by sodium deoxycholate. This property is most probably responsible of the deoxycholate-insensitive phenotype shown by strain 101/87. Phenotypic curing of strain 101/87 by externally adding purified LYTA or LYTA101 amidase restored in this strain some typical characteristics of the wild-type strain of pneumococcus (e.g., formation of diplo cells and sensitization to lysis by sodium deoxycholate), although the amount of the LYTA101 amidase required to restore these properties was much higher than in the case of the LYTA amidase. Our results indicate that modifications in the primary structure or in the mechanisms that control the activity of cell wall lytic enzymes seem to be responsible for the characteristics exhibited by some strains of S. pneumoniae that have been classically misclassified and should be now considered atypical pneumococcal strains.

Amidohydrolases↗
PubMed1992

EJ-1, a temperate bacteriophage of Streptococcus pneumoniae with a Myoviridae morphotype.

The first temperate bacteriophage (EJ-1) of Streptococcus pneumoniae with Myoviridae morphotype A1 isolated from a clinical atypical strain has been purified and characterized. This phage has a double-stranded linear genome about 42 kb long, but in contrast to the other pneumococcal temperate phages that have been characterized so far, EJ-1 does not contain any protein covalently linked to it. We have sequenced a fragment of EJ-1 DNA containing the ejl gene, encoding a cell wall lytic enzyme (EJL amidase). This gene has been cloned and expressed in Escherichia coli, and the EJL enzyme was purified and biochemically characterized as an N-acetylmuramyl-L-alanine amidase that shares many similarities with the major pneumococcal autolysin. The EJL amidase is a choline-dependent enzyme that needs the process of conversion to achieve full enzymatic activity, but in contrast to the wild-type pneumococcal LYTA amidase, this process was found to be reversible. Comparisons of the primary structure of this new lytic enzyme with that of the other cell wall lytic enzymes of S. pneumoniae and its bacteriophages characterized so far provided new insights as to the evolutionary relationships between phages and bacteria. The nucleotide sequences of the attachment site (attP) on the phage genome and one of the junctions created by the insertion of the prophage were determined. Interestingly, the attP site was located near the ejl gene, as previously observed for the pneumococcal temperate bacteriophage HB-3 (A. Romero, R. López, and P. García, J. Virol. 66:2860-2864, 1992). A stem-and-loop structure, some adjacent direct and inverted repeats, and two putative integration host factor-binding sites were found in the att sites.

Amino Acid Sequence↗
PubMed1992

Development of retinal displaced ganglion cells in the chick: neurogenesis and morphogenesis.

The time of birth of displaced ganglion cells (DGCs) was determined by autoradiography. DGCs start to leave the cell cycle early, on embryonic day 3, in the central and peripheral retina, and end on embryonic day 8, also in both areas of the retina. During the period of neurogenesis, unlabeled (born) DGCs do not appear distributed in spatial gradients as do the ganglion, amacrine, and other cell types in the retina (Prada et al., 1991). Our results show characteristic spatial and temporal patterns of DGC neurogenesis, which differ from those of the other retinal cell types. The morphogenesis of DGCs was studied by means of Golgi preparations. After leaving the cycle, DGC neuroblasts detach from the ventricular lining; they then move their soma through the vitreal process toward the final position at the same time that they emit the axon. Also during soma translocation, a transient sprouting of a few short processes is emitted from the vitreal process of the cell, close to where the soma is later located, suggesting that the "abnormal" position of DGCs could be specifically marked during the process of migration.

Animals↗
PubMed1992

Evaluation of total protein content in tears of dogs by polyacrylamide gel disk electrophoresis.

Concentration of total proteins was measured and sodium dodecyl sulfate-polyacrylamide gel disk electrophoresis was performed on tear and plasma samples obtained from 26 healthy dogs, and the results were compared. Mean +/- SEM concentration of total proteins in tears was 0.63 +/- 0.04 g/dl, and significant effects of age or gender were not found. The protein composition of tears in dogs was complex, and bands from light and heavy chains of immunoglobulins were identified by electrophoresis.

Age Factors↗
PubMed1992

Presence of Aedes (Gymnometopa) mediovittatus in Cuba: a new factor to be considered in the national campaign to eradicate dengue.

To assess the presence of the potential dengue vector Aedes mediovittatus relative to other mosquito species, data were examined from 44,199 larvitraps operating between January 1984 and December 1987 in the town of Mariel, Cuba. Of 1,068 larvitraps containing mosquitoes, 626 (58.6%) were positive for Ae. mediovittatus. Its relative presence increased each year except 1986, going from 37.9% of the positive traps in 1984 to 70.2% in 1987. More larvitraps were positive for Ae. mediovittatus than for Culex quinquefasciatus, which typically dominated breeding sites at the end of the intensive phase of the national campaign against Ae. aegypti in the early 1980s. The results appear to reflect Ae. mediovittatus' gradual infiltration into areas covered by the campaign, a factor that may need to be considered in efforts to control dengue in the Americas.

Aedes↗
PubMed1991

Chimeric pneumococcal cell wall lytic enzymes reveal important physiological and evolutionary traits.

Two novel chimeric pneumococcal cell wall lytic enzymes, named LC7 and CL7, have been constructed by in vitro recombination of the lytA gene encoding the major autolysin (LYTA amidase) of Streptococcus pneumoniae, a choline-dependent enzyme, and the cpl7 gene encoding the CPL7 lysozyme of phage Cp-7, a choline-independent enzyme. In remarkable contrast with previous chimeric constructions, we fused here two genes that lack nucleotide homology. The CL7 enzyme, which contains the N-terminal domain of CPL7 and C-terminal domain of LYTA, exhibited a choline-dependent lysozyme activity. This experimental rearrangement of domains might mimic the process that have generated the choline-dependent CPL1 lysozyme of phage Cp-1 during evolution, providing additional support to the modular theory of protein evolution. The LC7 enzyme, built up by fusion of the N-terminal domain of LYTA and the C-terminal domain of CPL7, exhibited an amidase activity capable of degrading ethanolamine-containing cell walls. The chimeric amidase behaved as an autolytic enzyme when it was cloned and expressed in S. pneumoniae. The chimeric enzymes provided new insights on the mechanisms involved in regulation of the host pneumococcal autolysins and on the participation of these enzymes in the process of cell separation. Furthermore, our experimental approach confirmed the basic role of the C-terminal domains in substrate recognition and revealed the influence of these domains on the optimal pH for catalytic activity.

Base Sequence↗
PubMed1991

Effects of dopamine-receptor antagonists and renal denervation on amino acid-induced hyperfiltration.

The mechanism whereby an infusion of amino acids (AA) leads to increments in glomerular filtration rate (GFR) and renal plasma flow (RPF) is incompletely understood. Dopamine (DA) is a catecholamine in which known actions at low doses include the ability to increase both GFR and RPF. Furthermore, urinary DA excretion has been shown to be augmented after an oral protein load. We therefore studied the renal hemodynamic response to intravenous infusion of a 10% mixed AA solution in anesthetized euvolemic Wistar-Furth rats in the presence or absence of specific DA1 [Sch 23390 (SCH)] and DA2 [S-sulpiride (S-SP)] receptor antagonists. Infusion of AA in vehicle-pretreated rats resulted in a 28 +/- 8% increase in GFR and a 29 +/- 6% increase in effective ERPF over baseline values. Administration of AA in the presence of SCH also resulted in elevations in both GFR and ERPF by 23 +/- 3% and 26 +/- 6%, respectively. In contrast, when AA were given in the presence of S-SP, the rise in both GFR and ERPF was completely prevented. To examine whether the AA-induced hyperfiltration was due to DA release from renal nerves or enhanced renal tubule DA synthesis, we administered AA to rats in which the left kidney had been chronically denervated while the right kidney remained intact. Infusion of AA led to significant increments in GFR (33 +/- 4%) and ERPF (34 +/- 7%) only in the intact control kidney, whereas GFR and ERPF remained unaltered in the denervated kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1991

[Adhesiveness in Neisseria meningitidis. A virulence factor?].

The role of adhesivity as a factor of virulence in cases of N. meningitidis has not yet been established. Unlike other bacteria in which the presence of adhesivity reflects an enhanced virulence, a high capacity of adherence is associated with a low virulence and invasive capacity in cases of meningococcus. In order to gain more insight into the knowledge of this phenomenon we have studied the adhesivity of 109 strains of N. meningitidis to human pharyngeal epithelial cells. Twenty nine out of the 109 strains were isolated from blood or spinal fluid of patients with meningococcal infection (meningitis or septicemia), whereas the remaining 80 strains were obtained from pharyngeal smears of healthy carriers. The adhesivity was measured as the number of meningococci adhered to 50 epithelial cells according to Craven's scale. Strains of healthy carriers showed a greater adhesivity than that of patients (p less than 0.001). The relevance of the pharyngeal area in the evaluation of the adhesive capacity is in accordance with the hypothesis that meningococcal adhesivity decreases when the microorganism crosses the pharyngeal epithelium. The results would support the concept that the virulence of N. meningitidis is related to its adhesiveness.

Bacterial Adhesion↗
PubMed1991

[Induction of Fc receptors and proliferative effect of recombinant human interleukins 1 and 2 (rhIL-1 and rhIL-2) on the leukemic lines WR19M.1 and WEHI3BD-].

Recombinant human interleukins 1 and 2 (rhIL-1 and rhIL-2) have recently been shown to interact with cells not only of the lymphoid lineage but also of myeloid origin. In fact, rhIL-1 indirectly stimulates normal haemopoietic cell proliferation without any influence on the differentiation, and can also induce lysozyme secretion by leukaemic cells. On the other hand, rhIL-2 is capable of indirectly stimulating the proliferation of monocytic precursors. Nevertheless, the effect of both factors on the expression of Fc receptors or on the proliferation of cells of myeloid origin has not been evaluated thus far. In order to assess whether these interleukins take part in the induction to proliferation of Fc receptor expression by homogeneous populations of myeloid cells, two leukaemic cell lines were used in this work, namely, WR19M.1, macrophagic, and WEHI3BD-, myelomonocytic. The results achieved show that: 1) rhIL-1 strongly stimulated the expression of Fc receptors in both leukaemic cell lines; 2) rhIL-1 does not stimulate the proliferation of these lineages; 3) on the contrary, rhIL-2 stimulated cell proliferation in both leukaemic cell lines, and 4) rhIL-2 had no effect on the induction of Fc receptors or on the stimulation of lysozyme secretion. The role played by the proliferative effect of rhIL-2, as well as the rhIL-1-mediated appearance of Fc receptors, in myeloid proliferation and differentiation are discussed.

Animals↗
PubMed1990

[T lymphoblastic leukemia with leukemoid reaction or the extramedullary blast crisis of Philadelphia chromosome-negative chronic myeloid leukemia? Comments apropos 2 cases].

Reactive leukocytosis has been reported in patients with non-Hodgkin's lymphoma of different histologic types. On the other hand, the blastic crisis of chronic myelocytic leukemia (CML) can sometimes be localized outside the bone marrow and simulate lymphoma, particularly when the blasts are of lymphoid lineage and the blastic crisis is the presenting feature of the disease. We report two patients in whom the differential diagnosis between lymphoblastic lymphoma with reactive leukocytosis and blastic crisis of CML outside the bone marrow was raised. They were two males aged 32 and 22 years, respectively, with lymphadenopathy (and one with splenomegaly), who were initially diagnosed of T lymphoblastic lymphoma. In both cases, leukocytosis was detected with myelemia and dysgranulopoiesis in the onset in one of them and when lymphadenopathy reappeared after remission in the other one. In addition, one patient had marked eosinophilia. In the bone marrow there was marked granulopoietic hyperplasia, with a reduction of fatty cells, and the granulocyte alkaline phosphatase index was reduced. However, the cytogenetic study did not disclose the existence of Philadelphia (Ph) chromosome, and bcr/abl molecular rearrangement was also not observed in the molecular study of both cases. We discuss the basic aspects of differential diagnosis between T lymphoblastic lymphoma with leukemoid reaction and T lymphoid lymphadenopathic blastic crisis of Ph-negative, bcr/abl-negative CML.

Adult↗