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Biomedical subjects

M M Silva

Publications and source records attributed to M M Silva.

33 records · Page 2Linked to original sources
PubMed1994

[Laboratory diagnosis of rabies in chiroptera carried out in a metropolitan area of southeastern region Brazil].

Between January, 1988 and December, 1992 the S. Paulo Animal Disease Control Center subjected 289 bats to rabies examinations, utilizing the direct immunofluorescence and biological techniques. Two insectiverous bats belonging to the species Nyctinomops macrotis, representing 0.69% of the total sample, tested positive. Both animals had been captured alive in residential neighborhoods of the city, one in 1988 in the living room of a 7th floor apartment and the other in 1990 on top of a wall surrounding a private house. In the biological tests, the disease showed incubation periods of 13 and 11 days respectively. Although the existence of infected insectiverous bats in urban areas is cause for concern, indiscriminate predatory action against such species can in no way be justified-particularly bearing in mind their importance in preserving the ecological balance of the insect population so prevalent in cities.

Animals↗
PubMed1993

Crystal structure of adenylosuccinate synthetase from Escherichia coli. Evidence for convergent evolution of GTP-binding domains.

The structure of the P2(1) crystal form of adenylosuccinate synthetase from Escherichia coli has been determined to a resolution of 2.8 A. The refined model for the enzyme gives an R factor of 0.20 and a root-mean-square deviation from expected bond lengths and angles of 0.016 A and 2.27 degrees, respectively. The dominant structural element of each monomer of the homodimer is a central beta-sheet of 10 strands. The first nine strands of the sheet are mutually parallel with right-handed crossover connections between the strands. The 10th strand is antiparallel with respect to the first nine strands. In addition, the enzyme has two antiparallel beta-sheets, comprised of two strands and three strands each, 11 alpha-helices and two short 3/10-helices. The overall fold of the polypeptide chain has not been observed heretofore in any other protein structure. Residues tentatively assigned to the active site of the enzyme on the basis of chemical modification and directed mutation cluster in two separate regions. Gly12, Gly15, Gly17, Lys18, Ile19, and Lys331 lie at one end of a crevice that measures 12 A by 30 A by 12 A deep. Lys140 and Arg147 are not part of this crevice, but instead lie at the interface between monomers of the dimer. Lys140 makes a salt link with Asp231 of a monomer related by molecular symmetry and Arg147 binds to the carbonyl of the same Asp231. Superposition of the p21 ras protein (Pai, E. F., Kabsch, W., Krengel, U., Holmes, K., John, J., and Wittinghofer, A. (1989) Nature 341, 209-214) onto the synthetase reveals significant correspondences between side chains of the two proteins. Residues which interact with GTP in the p21ras protein have structurally equivalent residues in the synthetase. The GTP molecule, when transformed to the coordinate frame of the synthetase, falls into the crevice defined by studies in directed mutation. We suggest that the similarities in the GTP-binding domains of the synthetase and the p21ras protein are an example of convergent evolution of two distinct families of GTP-binding proteins.

Adenylosuccinate Synthase↗
PubMed1993

Angiotensin converting enzyme inhibitors as oxygen free radical scavengers.

The authors have compared the ability of two non-SH-containing angiotensin converting enzyme (ACE) inhibitors (enalaprilat and lisinopril) with an -SH containing ACE inhibitor (captopril) to scavenge the hydroxyl radical (.OH). All three compounds were able to scavenge .OH radicals generated in free solution at approximately diffusion-controlled rates (10(10) M-1 s-1) as established by the deoxyribose assay in the presence of EDTA. The compounds also inhibited deoxyribose degradation in reaction mixtures which did not contain EDTA but not so effectively. This later findings also suggests that they have some degree of metal-binding capability. Chemiluminescence assays of oxidation of hypoxanthine by xanthine oxidase in the presence of luminol, confirm that the three ACE inhibitors are oxygen free radical scavengers. Our results indicate that the presence of a sulphydryl group in the chemical structure of ACE inhibitors is not relevant for their oxygen free radical scavenging ability.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

A third quaternary structure of human hemoglobin A at 1.7-A resolution.

Previous crystallographic studies have shown that human hemoglobin A can adopt two stable quaternary structures, one for deoxyhemoglobin (the T-state) and one for liganded hemoglobin (the R-state). In this paper we report our finding of a second quaternary structure (the R2-state) for liganded hemoglobin A. The magnitudes of the spatial differences between the R- and R2-states are as large as those between the R- and T-states. Of particular interest are the structural changes that occur as a result of R-T and R-R2 transitions at the so-called "switch" region of the critical alpha 1 beta 2 interface. In the R-state, His-97 beta 2 is positioned between Thr-38 alpha 1 and Thr-41 alpha 1, whereas in transition to the T-state His 97 beta 2 must "jump" a turn in the alpha 1 C helix to form nonpolar contacts with Thr-41 alpha 1 and Pro-44 alpha 1. This facet of the R-T transition presents a major steric barrier to the quaternary structure change. In the R2-state, His-97 beta 2 simply rotates away from threonines 38 alpha 1 and 41 alpha 1, breaking contact with these residues and allowing water access to the center of the alpha 1 beta 2 interface. With the switch region in an open position in the R2-state, His-97 beta 2 should be able to move by Thr-41 alpha 1 and make the transition to the T-state with a steric barrier that is less than that for the R-T transition. Thus the R2-state may function as a stable intermediate along a R-R2-T pathway. The T-, R-, and R2-states must coexist in solution. That is, the fact that these states can be crystallized implies that they are all energetically accessible structures. What remains to be determined are the T-to-R, T-to-R2, and R-to-R2 equilibrium constants for hemoglobin under various solution conditions and ligation states. Although this may prove to be difficult, we discuss previously published results which indicate that low concentrations of inorganic anions or low pH may favor the R2-state and at least one alpha 1 beta 2 interface mutation stabilizes a quaternary structure that is very similar to the R2-state.

Amino Acid Sequence↗
PubMed1992

[Angiotensin-converting enzyme inhibitors as neutralizers of hydroxyl radical].

Angiotensin converting enzyme inhibitors are utilized in the treatment of essential hypertension and of chronic cardiac failure. They are also employed in the treatment of the myocardial lesion of ischemia-reperfusion, which involves oxygen free radicals. In the present study we investigated the possibility of three angiotensin converting enzyme inhibitors (captopril, enalapril, lisinopril) to act as hydroxyl radical scavengers. The rate constants for reactions of those compounds with .OH were determined using the deoxyribose method. All there compounds proved to be good scavengers of .OH with rate constants of about 10(10)M-1s-1 and are iron chelators specially enalapril. The fact that captopril possesses a thiol group does not confer an higher antioxidative capacity. These results suggest that scavenging of oxygen free radicals may be a possible mechanism contributing to the therapeutic effect of angiotensin converting enzyme inhibitors.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Percutaneous sclerotherapy of varicocele.

Percutaneous sclerotherapy of varicocele was considered in 21 patients with left sided varicocele, 16 of whom had recurrences after left spermatic vein ligation in the past. Percutaneous sclerotherapy was possible in 17 patients (80.9%). There were no serious complications with venography or sclerotherapy, and the recurrence rate was 17.6%. Percutaneous sclerotherapy is therefore a simple, safe and effective treatment of testicular vein insufficiency.

Adolescent↗
PubMed1989

[Experience and results with a lactate dehydrogenase marker in vaginal secretions of women at high risk for endometrial cancer].

The authors present and discuss the results obtained with 202 Gynaegnost experiments in 161 women, between 45 and 65 years, nulliparous, or having experienced a late pregnancy, with menopause occurring after the age of 52 and undergoing or not estrogen-therapy after menopause, and presenting high blood pressure, obesity or diabetes. The purpose of this multicenter study, to be continued, was to demonstrate the efficacy of this tumor marker, in the early diagnosis of endometrial carcinoma, in high-risk women.

Aged↗
PubMed1987

The oxidase test in yeasts of medical importance.

The results of an oxidase test were positive with species of Cryptococcus and eight species of Candida, but negative with Candida krusei and species of Saccharomyces and Torulopsis, grown on Columbia Agar base and similar media, including Brain Heart Infusion Agar and Mueller Hinton Agar. When grown on Sabouraud Dextrose Agar, all the yeast genera and species were oxidase negative. The test is useful in delineating the genus Candida from Saccharomyces and Torulopsis.

Candida↗
PubMed1987

Purification and characterization of aminopeptidase activity from rat urine.

The aminopeptidase activity of rat urine was tested using L-aminoacyl-2-naphthylamides and L-Leu-p-nitroanilide. The enzyme preparation was purified by ion-exchange and gel filtration chromatography and showed only a single active protein band on 7.5% polyacrylamide gel electrophoresis. The enzyme was characterized by studying the effects of ions (divalent cations and chloride), chelating agents and -SH and -S-S- group reagents and by determining kinetic parameters (Km and Vmax for different substrates and Ki for amino acids, antibiotics and anti-inflammatory drugs).

Aminopeptidases↗
PubMed1982

AC polarographic determination of cloxacillin.

Hydrolysis of cloxacillin at pH 4.0 yields an electroactive product which can be determined by polarography. Depending on the concentration of cloxacillin, one of 2 peaks was obtained: The potential ac peaks for a 4.36 mM cloxacillin solution were peak I, -0.23 V and peak II, -0.13 V. For analytical purposes, the first peak was used. A linear relationship was established for levels of cloxacillin between 2.2 X 10(-5) and 2.2 X 10(-3)M. Average recovery was 98.8% (SD 1.8), indicating satisfactory accuracy for the method. Individual capsule and composite assays as well as interference tests are described.

Capsules↗
PubMedDate not supplied

[Benign prostatic hyperplasia. Guidelines and recommendations in urological clinical practice].

After reviewing the clinical, diagnostic and therapeutic attitudes related to benign prostatic hyperplasia, the authors present guidelines for generalists in what concerns practical attitudes and when and how to refer their patients to the urologist. Based on the criteria presented, generalists must refer their patients to a urologist in the presence of mild or severe symptoms, ages below 50, diabetes or neurological perturbations, dysfunctional voiding, palpable bladder, palpable nodule or a diffusely hardened or asymmetric gland revealed by digital rectal examination, haematuria, urinary tract infection, renal impairment or PSA above 4 ng/ml in patients under 70 years of age.

Adult↗