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Biomedical subjects

E Silva

Publications and source records attributed to E Silva.

At least 163 records · Page 9Linked to original sources
PubMed1983

Alpha- and beta- rat urinary kallikreins: chemical and physicochemical properties.

Alpha- and beta- urinary kallikreins were isolated by affinity chromatography on Sepharose-L-Arg-OMe (E. Silva, C.R. Diniz and M. Mares-Guia, Biochemistry, 13: 4304-4310, 1974). Both enzymes lowered rat arterial blood pressure and contracted the rat uterus. Alpha- and beta-kallikreins consist of single polypeptide chains of 27900 and 24900 daltons and have sedimentation coefficients of 2.49 S and 2.55 S, respectively. The alpha enzyme has 18 amino acid residues more than the beta enzyme and their carbohydrate content is 11.9% and 7.75%, respectively. Neuraminidase treatment removed all sialic acid residues from both forms and this improved their stability in aqueous solution at pH 7.0, 37 degrees C. After electrophoresis on 12% polyacrylamide gels at pH 8.3, followed by activity measurements of gel slices with H-D-Val-Leu-Arg-pNA, two active bands each were detected for alpha and beta-kallikrein, but in different proportions and with different specific activity. On the basis of the rat uterus assay, alpha-kallikrein was three times more active than beta-kallikrein. The amino acid composition of alpha-kallikrein is strikingly similar to that of pig kallikrein B and human urinary kallikrein.

Animals↗
PubMed1981

Isolation and photo-oxidation of lysozyme fragments.

Reduction of the four disulfide bonds and further carboxymethylation of lysozyme followed by its reaction with CNBr brings about L-I, (aa 1-12) and L-II-III (aa 13-129) peptides. When breaking the polypeptidic chain by CNBr action and freeing the peptides formed through S-S bonds reduction and carboxymethylation three peptides are obtained corresponding to L-I (aa 1-12), L-II (aa 13-105) and L-III (aa 106-129). L-II-III, L-III and L-II peptides were separately subjected to photo-oxidation in presence of riboflavin, in 0.05 M phosphate buffer, pH 7.0. The kinetic analysis of Trp photo-oxidation in L-II-III peptides shows that these residues keep, to a great extent, the degree of exposition they had in native lysozyme. L-II peptide also presents Trp residues with a different degree of exposition. Presence of Tyr photo-oxidation in L-II and L-II-III peptides - what does not take place in native lysozyme - suggests a relationship between photo-oxidation selectivity and the degree of exposition of certain amino acid residues in spatial configuration.

Amino Acids↗
PubMed1981

[Clinical evaluation of pipothiazine and its palmitic ester in the therapy of schizophrenia].

20 schizophrenic patients presenting with an acute episode were treated first, whilst hospitalized, by a single oral dose of pipotiazine, then, when their symptomatology had been controlled, thus allowing their discharge, by a monthly injection of pipotiazine palmitate for 6 months. The patients were assessed with a CGI and the BPRS. The tablets provided control of the symptoms of most patients as early as the second week of treatment, the improvement bearing particularly on thought disorder, concept disorganization, excitation, anxiety, depression, tension and somatic symptoms. This led to an improvement in activities and sociability. Injections not only provided the prevention of relapses but even an improvement over the already obtained results which allowed these patients to insert themselves in the community. Adverse effects were infrequent and easily controlled. There were no abnormal modifications of the vital signs and laboratory tests. Pipotiazine appears as an extremely useful drug for countries in which the psychiatric treatment network is still being constructed.

Acute Disease↗
PubMed1981

Mediastinal mass with acute leukemia. Myeloblastoma masquerading as lymphoblastic lymphoma.

Acute leukemia of myeloblastic or myelomonocytic type after non-Hodgkin's lymphoma is a recognized complication of radiotherapy or chemotherapy. However, a few reports suggest spontaneous development of, or coexistent, acute myeloblastic or myelomonocytic leukemia in patients with non-Hodgkin's lymphoma, unrelated to therapy. We studied a case initially interpreted as being lymphoblastic lymphoma with spontaneous acute leukemia, but subsequently shown by cytochemical and ultrastructural studies to be myeloblastoma. We reviewed the previously reported cases of non-Hodgkin's lymphoma with spontaneous myeloid leukemia in the light of our findings, and such cases may, in fact, represent myeloblastomas (granulocytic sarcomas) rather than non-Hodgkin's lymphoma.

Aged↗
PubMed1979

Rate constants studies of the dye-sensitized photoinactivation of lysozyme.

The rate constants for the photodynamic inactivation of hen egg-white lysozyme at different temperatures were studied. Arrhenius plots of the methylene blue sensitized photo-inactivation of lysozyme gave an experimental activation energy of 7.5 kcal/mol. The rate constants for the photodynamic inactivation of lysozyme in the presence of riboflavin decreased almost linearly in the temperature range 4-38 degrees C. The photosensitized oxidation of lysozyme at -20 degrees C in freezing and non-freezing solvents was possible only in the presence of riboflavin. The effect of dye concentration on the quantum yield and rate constant for the photodynamic inactivation of lysozyme was examined. The quantum yields were lower when the concentrations of methylene blue used were low, and increased on increasing dye concentration, getting to a maximum and then declined at higher dye concentrations. It was found that in the case of riboflavin sensitized photo-inactivation of lysozyme both the rate constant and the quantum yield increased as the dye concentration increased. No maximum was observed over the range of dye concentrations studied. A new mechanism is postulated for the photodynamic action of lysozyme in the presence of riboflavin.

Chemical Phenomena↗
PubMed1977

Light-induced binding of riboflavin to lysozyme.

The photodynamic inactivation of lysozyme in air saturated H2O and D2O (phosphate buffer 0.05 M, pH 7.0) in the presence of methylene blue and riboflavin has been studied. When H2O was replaced by D2O a great increase in the rate of photoinactivation of lysozyme was observed. This finding, together with the fact that photooxidation is inhibited by singlet oxygen quenchers like NaN3, suggests that these reactions occur via a singlet oxygen mechanism. During the course of the studies of the riboflavin sensitized photoinactivation of lysozyme, it was found that riboflavin is strongly bound to the enzyme as a result of illumination. This finding would explain the higher quantum yield observed when riboflavin is used, although this dye is bleached during irradiation.

Chemical Phenomena↗
PubMed1977

Stimulation of hepatic mitochondrial alpha-glycerophosphate dehydrogenase and malic enzyme by L-triiodothyronine. Characteristics of the response with specific nuclear thyroid hormone binding sites fully saturated.

Experiments were designed to analyze the relationship of a single i.v. dose of triiodothyronine (T3), the level of plasma and hepatic nuclear T3 attained, and the tissue response as reflected in increased activity of hepatic mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytosol "malic enzyme" (ME). These studied were carried out in euthyroid rats by varying the dose of T3 injected and the time at which the animals were killed and the enzyme levels measured. The plasma T3 concentration was determined and the fraction of nuclear sites occupied at any time t was calculated from the known plasma:nuclear relationship. As a first step, the analysis was confined to the limiting situation in which all nuclear sites were effectively saturated. The following additional information was required and obtained: A proportional relationship between the half-neutralizing volume of a specific antiserum to malic enzyme and the activity of malic enzyme was established, thus confirming previous reports that the increase in enzyme activity induced by T3 is due to increased enzyme mass. The absolute refractory period immediately after i.v. injection of T3, during which no enzyme response could be detected, was determined. This was shown to be 13.4 h for alpha-GPD and 8.2 h for ME. Lastly, the t1/2 of the enzyme decay after pulse injection of T3 was measured. This was similar for both enzymes, 2.8+/-0.6 (SD) days for alpha-GPD and 2.7+/-0.6 (SD) days for ME. The results of these studies indicated that the extent of hepatic response appears limited by full occupancy of a set of intracellular receptor sites by T3 which is in rapid equilibrium with the plasma hormone pool. The kinetic properties of the receptors, as functionally defined in these studies, resemble those associated with the recently described specific nuclear T3 sites. These data per se are thus compatible with but do not prove a nuclear site of initiation of hormone effect. Thye do allow the development of an internally consistent mathematical model which permits prediction of enzyme response when the receptor sites are fully occupied for a given length of time after the i.v. injection of hormone. A separate series of studies was carried out in thyroidectomized rats. The response characteristics of alpha-GPD were similar to those observed in euthyroid animals. In contrast, however, the early response of ME to pulse injections of T3 was very much reduced in hypothyroid animals as compared to euthryoid animals in which nuclear sites were saturated for comparable periods. These findings raise the possibility that a factor required for the induction of malic enzyme but not alpha-GPD is deficient in the hypothyroid state.

Animals↗
PubMed1977

Alpha-amanitin administration results in a temporary inhibition of hepatic enzyme induction by triiodothyronine: further evidence favoring a long-lived mediator of thyroid hormone action.

Alpha-amanitin was shown to inhibit triiodothyronine (T3)-induced increases in mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytoplasmic malic enzyme activity in the livers of male Sprague-Dawley rats. A 3-fold increase in alpha-GPD observed 24 h after the iv injection of 3 microngT3/100 g BW was completely inhibited by administration of alpha-amanitin at 0 and 8 h. Similarly, alpha-amanitin blocked a two- to four-fold increase in malic enzyme 24 h following iv injection of 3 mg T3/100 g BW into euthyroid rats. After the initial inhibition of enzyme induction by alpha-amanitin was dissipated, however, a delayed but striking increase in enzyme activity occurred. In hypothyroid animals, alpha-GPD activity rose after the initial 24 h inhibition and reached levels at 72 h equal to those observed in hypothyroid rats treated with T3 only. In euthyroid animals treated with T3 and alpha-amanitin, a delayed increase in malic enzyme activity was observed at 72 h and attained values at 96 h similar to those in euthyroid animals injected with T3 only. The delayed rise in enzyme response is most easily explained by the formation of a long-lived intermediate during the exposure of the nuclear sites to T3.

Amanitins↗
PubMed1977

Studies of a thyroid hormone and androgen dependent protein in rat liver cytosol.

Sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis of the liver cytosol of euthyroid male rats revealed a prominent band (molecular weight, 26 000 daltons), designated Protein II, which was virtually absent in the cytosol of hypothyroid animals. Injection of 500 mug triiodothyronine (T3) per 100 g body weight resulted in a maximal increase in the level of Protein II, reaching 90% of the euthyroidal level 3 days after hormone administration. Concomitant studies with the liver mitochondrial enzyme alpha-glycerophosphate dehydrogenase (alpha-GPD) indicated that this T3 dose also resulted in a maximal enzyme response in this time period. Since we have estimated that 500 mug of T3 will saturate nearly all nuclear T3 binding sites, these results support the concept that the synthesis of both proteins is limited by nuclear binding. Protein II was absent in the liver cytosol of female rats but could be induced in ovariectomized female rats by androgens. Treatment of male rats with oestradiol resulted in disappearance of Protein II. Since administration of testosterone to hypothyroid male rats caused only a minimal increase in the amount of Protein II, the absence of the protein in hypothyroid animals was not due to androgen deficiency. Similarities in the molecular weight and the response to hormonal manipulation of Protein II and of the urinary alpha2uglobulin, previously reported by Roy (1973) raise the possibility that these proteins are the same. The high concentration of Protein II in male rat cytosol and the relative ease in its identification by SDS polyacrylamide gel electrophoresis make it a potentially useful model protein for the study of thyroid hormone action at the cellular level.

Animals↗