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N Silva

Publications and source records attributed to N Silva.

At least 37 records · Page 2Linked to original sources
PubMed1994

13C NMR and fluorescence analysis of tryptophan dynamics in wild-type and two single-Trp variants of Escherichia coli thioredoxin.

The rotational motion of tryptophan side chains in oxidized and reduced wild-type (WT) Escherichia coli thioredoxin and in two single-tryptophan variants of E. coli thioredoxin was studied in solution in the temperature range 20-50 degrees C from 13C-NMR relaxation rate measurements at 75.4 and 125.7 MHz and at 20 degrees C from steady-state and time-resolved trp fluorescence anisotropy measurements. Tryptophan enriched with 13C at the delta 1 and epsilon 3 sites of the indole ring was incorporated into WT thioredoxin and into two single-trp mutants, W31F and W28F, in which trp-28 or trp-31 of WT thioredoxin was replaced, respectively, with phenylalanine. The NMR relaxation data were interpreted using the Lipari and Szabo "model-free" approach (G. Lipari and A. Szabo. 1982. J. Amer. Chem. Soc. 104:4546-4559) with trp steady-state anisotropy data included for the variants at 20 degrees C. Values for the correlation time for the overall rotational motion (tau m) from NMR of oxidized and reduced WT thioredoxin at 35 degrees C agree well with those given by Stone et al. (Stone, M. J., K. Chandrasekhar, A. Holmgren, P. E. Wright, and H. J. Dyson. 1993. Biochemistry. 32:426-435) from 15N NMR relaxation rates, and the dependence of tau m on viscosity and temperature was in accord with the Stokes-Einstein relationship. Order parameters (S2) near 1 were obtained for the trp side chains in the WT proteins even at 50 degrees C. A slight increase in the amplitude of motion (decrease in S2) of trp-31, which is near the protein surface, but not of trp-28, which is partially buried in the protein matrix, was observed in reduced relative to oxidized WT thioredoxin. For trp-28 in W31F, order parameters near 1 (S2 > or = 0.8) at 20 degrees C were found, whereas trp-31 in W28F yielded the smallest order parameters (S2 approximately 0.6) of any of the cases. Analysis of time-resolved anisotropy decays in W28F and W31F yielded S2 values in good agreement with NMR, but gave tau m values about 60% smaller. Generally, values of tau e, the effective correlation time for the internal motion, were < or = 60 ps from NMR, whereas somewhat longer times were obtained from fluorescence. The ability of NMR and fluorescence techniques to detect subnanosecond motions in proteins reliably is examined.

Carbon Isotopes↗
PubMed1993

Molten globule monomers in human superoxide dismutase.

The time-resolved fluorescence decay and anisotropy of Cu/Zn human superoxide dismutase (HSOD) were studied as a function of temperature and denaturant concentration. In addition, circular dichroism (CD) measurements were performed on HSOD as a function of denaturant concentration in the amide and aromatic regions. The time-resolved fluorescence decay results reveal the existence of structural microheterogeneity in HSOD. Furthermore, CD measurements and a global analysis decomposition of the time-resolved fluorescence decay over denaturant concentration shows the presence of an intermediate in the unfolding of HSOD by guanidinium hydrochloride. Considering our previous measurements of partially denatured HSOD as a function of protein concentration (Mei et al., Biochemistry 31 (1992) 7224-7230), our results strongly suggest that the unfolding intermediate is a monomer that displays a molten globule state.

Circular Dichroism↗
PubMed1993

Characteristics of the acquired immunodeficiency syndrome in Brazil.

The clinical and epidemiologic characteristics of the acquired immunodeficiency syndrome (AIDS) were studied in a tropical area of Brazil. During an 18-month period (July 1989-January 1991), 111 consecutive AIDS patients (102 men and nine women) were evaluated. Patients reported homosexual/bisexual activities (60%), intravenous drug use (19%), or both (6%), heterosexual activities (11%), blood transfusions (2%), and 2% belonged to an undetermined category. Weight loss, fever, oral thrush, and diarrhea were present in > or = 70% of the patients at presentation. An unexpected high frequency of hepatomegaly (49%) was detected, and found to be significantly associated with tuberculosis (P < 0.0001). Although the epidemiologic features of human immunodeficiency virus transmission were comparable to the United States/European pattern, the clinical spectrum of opportunistic infections more closely resembled that reported in Africa and Haiti, with a greater frequency of fungal and mycobacterial infections than Pneumocystis carinii pneumonia and viral infections.

AIDS-Related Opportunistic Infections↗
PubMed1993

Serologic validation of HIV infection in a tropical area.

We have defined human immunodeficiency virus type 1 (HIV-1) serologic reactivity in Brazilians living in an area endemic for tropical diseases. Enzyme-linked immunosorbent assay (ELISA) and Western blot (WB) analyses were performed on 342 patients with diseases including Chagas' disease, schistosomiasis, typhoid fever, helminthiasis, and cutaneous and visceral leishmaniasis. Nine percent of the visceral leishmaniasis patients' sera reacted in the HIV-1 ELISA but all were WB negative. All other sera from these patients were HIV negative. A total of 224 HIV-1 ELISA repeatedly positive sera also were HIV-1 WB tested. They were drawn from a total population of 19,230 individuals, including AIDS patients, blood donors, homosexual men, intravenous drug users, pregnant women, individuals with hemophiliac, and tuberculosis and sexually transmitted disease patients. The WB results were analyzed using five different interpretive criteria for WB positivity. The Centers for Disease Control (CDC) and the World Health Organization (WHO) criteria were the most sensitive and specific for identifying HIV-1-infected individuals. The WB pattern was similar to that seen in the United States. Envelope (ENV) protein antibodies were highly predictive of HIV-1 infection; none of the AIDS patients lacked ENV protein reactivity. We conclude that among the tropical diseases studied, only visceral leishmaniasis is associated with false-positive HIV-1 ELISA tests. Current CDC and WHO criteria for interpretation of HIV-1 WB tests are appropriate for Brazil.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Denaturation of human Cu/Zn superoxide dismutase by guanidine hydrochloride: a dynamic fluorescence study.

The unfolding of holo and apo forms of human Cu/Zn superoxide dismutase by guanidine hydrochloride has been investigated by steady-state and dynamic fluorescence. In agreement with previous observations, a stabilizing effect of the metal ions on the protein tertiary structure was apparent from comparison of apo- and holoproteins, which both showed a sharp sigmoidal transition though at different denaturant concentrations. The transition was also followed by circular dichroism to check the extent of secondary structure present at each denaturant concentration. The results are incompatible with a simple two-state mechanism for denaturation. The occurrence of a more complicated process is supported by the emission decay properties of the single tryptophanyl residue at different denaturant concentrations. A complex decay function, namely, two discrete exponentials or a continuous distribution of lifetimes, was always required to fit the data. In particular, the width of the lifetime distribution, which is maximum at the transition midpoint, reflects heterogeneity of the tryptophan microenvironment and thus the presence of different species along the denaturation pathway. In the unfolded state, the width of the lifetime distribution is broader than in the folded state probably because the tryptophan residue is affected by a larger number of local conformations. The dissociation of the dimer was also studied by varying the protein concentration at different denaturant concentrations. This process affects primarly the surface of the protein rather than its secondary structure as shown by a comparison between the tryptophan emission decay and circular dichroism data under the same conditions. Another consequence of dissociation is a greater instability in the structure of the monomers, which are more easily unfolded.(ABSTRACT TRUNCATED AT 250 WORDS)

Apoenzymes↗
PubMed1992

Comparison of gastric intramucosal pH with measures of oxygen transport and consumption in critically ill patients.

OBJECTIVE: To determine the relationship of tonometrically measured gastric intramucosal pH to clinically accepted indices of systemic oxygenation. DESIGN: Prospective, nonintervention study. SETTING: Medical and surgical ICUs of a university hospital. PATIENTS: Critically ill patients (n = 22) with pulmonary artery catheters in place who also required nasogastric suctioning. MEASUREMENTS AND MAIN RESULTS: Tonometric measurements of gastric intramucosal pH were compared with concurrently obtained systemic indices of tissue oxygenation. These variables included oxygen delivery (DO2), oxygen consumption (VO2), oxygen extraction ratio, arterial lactate concentrations, mixed venous PO2, and mixed venous pH. The study period ranged from the time of insertion of the pulmonary artery catheter to the time of its removal. We classified patients who were alive by the end of the study as survivors and those patients who died with the pulmonary artery catheter in place as nonsurvivors. Both groups had similar levels of DO2 during the study period, but nonsurvivors had greater levels of VO2, oxygen extraction ratio, and serum lactate concentrations than survivors. Gastric intramucosal pH, mixed venous pH, and mixed venous PO2 values were lower in nonsurvivors. Both groups demonstrated the phenomenon of oxygen supply dependency. When the final measurements taken before the removal of the pulmonary artery catheter or death were compared, only gastric intramucosal pH and mixed venous pH showed differences between the groups, being lower in nonsurvivors. All the patients who died, except for one, had final gastric intramucosal pH values of less than 7.32. CONCLUSIONS: In this group of patients, death was associated with increased tissue needs for oxygen that were not adequately satisfied by the available levels of oxygen supply. We also conclude that tonometrically measured gastric intramucosal pH is a useful noninvasive adjunct to current methods of monitoring systemic oxygenation.

Adult↗
PubMed1992

Role of tissue hypoxia as the mechanism of lactic acidosis during E. coli endotoxemia.

We compared the hemodynamic and metabolic alterations produced in rabbits by similar decreases in cardiac output created by inflating a balloon placed in the right ventricle (n = 6) with those produced by an intravenous bolus of Escherichia coli lipopolysaccharide (LPS; SEP group; n = 6). We measured O2 consumption (VO2), O2 transport (TO2), and O2 extraction ratio (ERO2) for the whole animal and also for the left hindlimb. Both groups experienced similar decreases in cardiac output, systemic TO2, and VO2 and similar increases in ERO2. For the hindlimb, TO2 was similar, but VO2 and ERO2 were lower for the SEP group 30 min after LPS administration (P less than 0.05); however, this difference disappeared during the remainder of the experiment. Arterial lactate concentration was greater (P less than 0.05) for the SEP group. There were no differences in skeletal muscle PO2, measured with a multiwire surface electrode, or in cardiac and skeletal muscle concentrations of high-energy phosphates. We hypothesize that a direct effect of LPS on cellular metabolism may have resulted in greater arterial lactate concentration for the SEP group.

Acidosis, Lactic↗
PubMed1991

[Characterization of collagen of canine intervertebral disks using the N-methyl-benzothiazol-2-on-hydrazone reaction].

Collagen types were studied in the lumbar intervertebral discs of non-chondrodystrophic dogs, 1 to 3 years old. Parts of intervertebral discs were frozen and sections were subjected to the 3-methyl-benzothiazol-2-on-hydrazone (MBTH) method, which permits differentiation of genetic types and maturation stages of collagen. The annulus fibrosus showed a blue (collagen I) and a violet colour (collagen II) at the external zone. The internal zone was more homogeneous and contained a mixture of both colours (collagen I and II). The nucleus pulposus showed only the violet colour, indicative of collagen II. Discs were also dissected at three different zones and submitted to an extraction technique to obtain collagen, then subjected to SDS-polyacrylamide gel electrophoresis and determination of spectrophotometric reactions of MBTH. Both studies demonstrated type I and type II collagens in the external and internal zones of the annulus fibrosus, but only type II in the nucleus pulposus. Collagen characterization, using this technique, would allow for evaluation in pathologic events of the intervertebral discs as well as for establishing the degree of alteration.

Animals↗
PubMed1989

[Prevalence of Streptococcus mutans in pehuenche children, Chilean ethnic group].

We studied 26 pehuenche children between 9 and 13 years of age and 12 non-pehuenche controls. Samples were obtained from saliva and from the bacterial plaque of 6 year molars and cultured anaerobically for 48 hr at 37 C in TYCSB medium. S mutans were obtained from 90% of children in both groups, all corresponding to biotype I (Coykendall). Nutritional and hygienic habits did not differ between groups. These results confirm the ample distribution of S mutants in Chilean subjects.

Adolescent↗
PubMed1988

R.N.s' Rx for H.I.S.

Changes in today's healthcare industry are placing new and continued demands on providers. This has resulted in a growing emphasis on more efficient communications between departments, increased staff productivity and a renewed commitment to quality patient care. A tool hospitals use to respond to these needs is a computerized hospital information system (HIS).

Decision Making↗
PubMed1985

Early physiologic changes in canine fecal peritonitis.

Oxygen delivery (DO2) and related variables were studied in eight dogs during severe untreated peritonitis induced by cecal ligation and perforation. The development of peritonitis was accompanied by abdominal fluid sequestration and significant increases in hemoglobin (Hgb), arterial oxygen content (CaO2), and P50. Changes in mixed venous PO2 (P-vO2), mixed venous saturation (S-vO2), DO2, oxygen uptake (VO2), cardiac index (CI), and arteriovenous O2 difference (C[a--v]O2) were not significant. When blood volume was returned to normal levels with dextran, CI rose and C(a--v)O2 decreased; P-vO2 increased and Hgb returned to baseline levels. In this animal model, sepsis and fluid sequestration produced an increase in blood O2 capacity and CaO2, which sustained DO2 and VO2. No changes were observed in P-vO2 or S-vO2. The hyperdynamic state of severe sepsis became evident only after reversing hemoconcentration by colloid infusion. The increase in P-vO2 and S-vO2 after volume loading is possibly related to primary septic mechanisms and/or to changes in DO2.

Animals↗
PubMed1977

Partial horizontal supraglottic laryngectomy. A method of reconstruction.

Despite the low occurrence of early laryngeal lesions amenable to Partial Supraglottic Laryngectomy, they form a very interesting and important group of lesions. Timing is important in their recognition, since adequate treatment can then be secured and important functions of the larynx preserved. The draw back in the treatment of these lesions by partial laryngectomy lies in the difficulty in restoring the patient to his preoperative pattern of life. Repeated aspiration pneumonitis becomes a life threatening problem in a good number of such patients. A new method of reconstruction is described here by which the aspiration problem is obviated with the aid of a pedicle flap to line the raw surface of the transected base of the tongue allowing the organ to remain in a position capable of occluding the glottis during deglutition, and at the same time guiding the food along the posterior pharyngeal wall and into the esophagus.

Humans↗