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Biomedical subjects

G Weber

Publications and source records attributed to G Weber.

At least 433 records · Page 24Linked to original sources
PubMed1987

Regulation by insulin of liver carbamoyl-phosphate synthase II (glutamine-hydrolysing).

Evidence is provided that insulin controls the amount and synthetic rate of liver carbamoyl-phosphate synthase II (EC 6.3.5.5) (synthase II) in rat. In 3- and 6-day starvation, with low plasma insulin, synthase II specific activity decreased to 47 and 30%, respectively, of normal; on re-feeding and with concurrent insulin injections, liver synthase II activity increased to 2.5 and 3 times that of starved rats respectively. Treatment with anti-insulin serum during re-feeding prevented the rise in synthase II activity. In diabetic rats, synthase II activity decreased to 28% of normal and was increased by insulin treatment for 2 and 7 days to 4.8- and 5.6-fold of the activity in diabetic liver; this rise in activity was blocked by actinomycin. Immunotitration demonstrated that alterations in synthase II activity were due to changes in the enzyme amount. In starvation, the relative synthesis rate of synthase II decreased to 44%, with an increase in catabolic rate to 122%; re-feeding returned these to control values. In diabetes the synthase II synthesis rate decreased to 52% and the degradative rate was accelerated to 180%; insulin treatment induced synthesis and returned degradation to the control range. Thus the integrative action of insulin in liver pyrimidine metabolism entails regulation of the amount and turnover of synthase II.

Animals↗
PubMed1987

Free energy couplings between ligand binding and subunit association in hemoglobin are of first order.

The calculations presented in a recent paper [Johnson, M. L. (1986) Biochemistry 25, 791-797] to the effect that the free energy couplings between oxygen binding and subunit association in hemoglobin A can be of either first or second order are examined. The fitting of the experimental data to a system with second-order couplings carried out by Johnson belongs to a tetramer in which, in contradistinction to hemoglobin A, oxygen binding promotes subunit association.

Hemoglobins↗
PubMed1987

Serum zinc and copper as prognostic factors in acute nonlymphocytic leukemia.

A total of 44 patients were treated with intensive induction chemotherapy for acute nonlymphocytic leukemia (ANLL). A complete remission (CR) was obtained in 29/44 (66%) patients. Serum zinc (Zn) and copper (Cu) were studied as possible prognostic factors in the determination of the chance of a patient attaining remission. Pretreatment Zn was higher in patients attaining a remission (0.99 +/- 0.05 microgram/ml) than in patients failing to attain a CR (0.78 +/- 0.06 microgram/ml) (P = 0.0216). There was no further difference between the two groups during aplasia. However, when response to treatment was evaluated about day 28, the difference reappeared: 1.06 +/- 0.05 microgram/ml for CR patients vs 0.77 +/- 0.07 microgram/ml for failures (p = 0.0012). Pretreatment Cu was higher in responding (1.44 +/- 0.07 microgram/ml) than in nonresponding (1.06 +/- 0.05 microgram/ml) patients (p = 0.0002). The difference between the two groups remained highly significant at days 7, 14, 21, and 28. At the time of response evaluation, the values were 1.46 +/- 0.05 microgram/ml for CR patients vs 1.19 +/- 0.08 microgram/ml for non-CR patients (P = 0.0070). We conclude that the measurement of serum Zn and Cu may be helpful in the prediction of response to chemotherapy in patients treated for ANLL.

Acute Disease↗
PubMed1987

Isolated glucocorticoid deficiency.

A three-month-old boy with hypoglycemic episodes, feeding problems and hyperpigmentation is described. Hormone assays revealed elevated serum ACTH values and low levels of plasma cortisol that did not rise after exogenous ACTH administration; blood pressure, serum electrolytes and earlier plasma aldosterone and renin activity were in the normal range. These data suggest a diagnosis of an isolated glucocorticoid deficiency, secondary to unresponsiveness to ACTH. Replacement therapy with glucocorticoids was highly effective. Despite replacement therapy, during follow-up he had an increase in basal plasma renin activity with aldosterone concentration normal. In our patient, a mineralcorticoid deficiency might eventually develop; therefore, the selective glucocorticoid deficiency might also be part of a progressive defect involving the glomerulosa too.

Aldosterone↗
PubMed1987

Simple separation of tritiated water and [3H]deoxyuridine from [5-3H]deoxyuridine 5'-monophosphate in the thymidylate synthase assay.

A simple micromethod was developed for the accurate measurement of the activity of dTMP synthase in rat liver crude extracts. The reaction product of dTMP synthase activity assay, i.e., tritiated water, generated by the release of tritium from carbon-5 of [5-3H]deoxyuridine 5'-monophosphate (dUMP), was separated simply by 100% KOH absorption from [5-3H]deoxyuridine (dUrd), which is the side-product by dephosphorylation of [5-3H]deoxyuridine (dUrd), which is the side-product by dephosphorylation of [5-3H]dUMP during the enzyme reaction. Tritiated water was trapped in three droplets of 100% KOH deposited on the underside of the vessels' lids, while [3H]dUrd remained in the bottom of vessels after absorption of the substrate, [5-3H]dUMP, from the reaction mixture by charcoal treatment. Under standard assay conditions in the crude extract of rat liver, the specific activities of dTMP synthase and dUMP phosphatase were 0.092 +/- 0.002 and 0.351 +/- 0.013 nmol/h/mg protein, respectively. This method was also adapted for dTMP synthase assay in crude extracts of rat hepatoma 3924A. The major advantages of this procedure are the elimination of the phosphatase activity which interferes with the estimation of dTMP synthase activity in crude extracts, one-step separation of 3H2O, high sensitivity (with a limit of detection of 10 pmol of 3H2O production), high reproducibility (less than +/- 4.3%), and capability to measure activity in small amounts of sample (30-45 micrograms protein).

Animals↗
PubMed1987

Slab gel electrophoresis of oligomeric proteins under high hydrostatic pressure. I. Description of the system and demonstration of the pressure dissociation of a dimer.

A high-pressure bomb was constructed to study the gel electrophoretic behavior of oligomeric proteins under pressure. The apparatus designed by us allows the use of a polyacrylamide slab gel with a capacity of up to 12 wells, therefore permitting the study of several samples in one experiment. The electrophoresis mobility of different single-chain proteins under pressure decreased in the same proportion and the elution pattern was similar to that of the control run at atmospheric pressure. Densitometric analysis of the gel did not show peak spread or asymmetric boundaries, indicating that their conformations were not drastically affected. On the other hand, high-pressure electrophoresis of a dimer, the tryptophan synthase beta 2 subunit, revealed the appearance of a second peak not present at atmospheric pressure. The mobility of the second peak was higher and its fraction increased by decreasing the protein concentration, indicating that the extra peak was the dissociated monomer. The separation under pressure occurs without drastic effects on the tertiary structure of the protein, which seems to furnish a method to study dissociation processes and to separate the constituent polypeptides of oligomeric complexes.

Electrophoresis, Polyacrylamide Gel↗
PubMed1987

The increase of the openings of the surface-connected canalicular system in weakly stimulated platelets is prevented by a carbochromen derivative. A computerized morphometric analysis of freeze-etched human platelet plasma-membrane.

When thrombin is added to platelet rich plasma at very low concentrations (0.02 U/ml), platelets undergo an activation process. Under these conditions platelets discharge beta-thromboglobulin, platelet factor 4 and the "platelet derived growth factor". In this paper we present evidence that when human platelets are weakly stimulated with thrombin, the number of openings of the surface connected canalicular system (SCCS) increases. This was observed ultrastructurally by the freeze-etching technique. 8-chlorocarbochromen, an antiaggregating drug, seems to inhibit this increase.

Adult↗
PubMed1987

Salvage pathways as targets of chemotherapy.

This paper discussed the significance of the activities of purine and pyrimidine salvage enzymes in cancer cells and the targeting against them of chemotherapy. 1. The activities of salvage enzymes in the rat liver were orders of magnitude higher than those of the rate-limiting enzymes of de novo biosynthesis. A similar relationship was observed in rat hepatomas of different growth rates and in primary colon carcinoma in human. 2. The concentrations of nucleosides and nucleobases were measured in plasma, liver and hepatoma 3924A in the rat. The freeze-clamp method was required to determine the concentrations of these precursors in rat liver and hepatoma in a reliable and precise fashion because ischemia markedly altered the concentrations of nucleosides, nucleobases and, as shown earlier, nucleotides in these tissues. The results indicated that the liver markedly concentrated the purine precursors, hypoxanthine, guanine and adenine, but not thymidine, which was one-third that of the plasma. Uridine and deoxycytidine occurred in the same concentration as in plasma, but cytidine was 3-fold higher in liver. In the hepatoma in comparison to the liver the concentrations of the nucleosides and bases were altered and for some of the changes the enzymic differences between liver and hepatoma appeared to be accountable. 3. Kinetic parameters for purine and pyrimidine synthetic enzymes and for the substrates and co-factors were determined in liver and hepatoma 3924A. When enzymic activities were calculated at the tissue steady-state concentrations of the various ligands, the activities of the salvage enzymes were markedly higher than those of the rate-limiting enzymes. 4. Hepatoma cells were highly sensitive to the action of the transport inhibitor, dipyridamole, in lag and log phases. However, plateau phase cells lost their sensitivity to dipyridamole. 5. Amphotericin B rendered plateau phase cells sensitive to the inhibitory action of dipyridamole for the incorporation of thymidine. 6. Amphotericin B enhanced cytotoxicity of dipyridamole in hepatoma and human colon cancer HT-29 cells. 7. In these studies we discovered the decreased responsiveness to dipyridamole of plateau phase cells and the ability of amphotericin B to restore the sensitivity. Moreover, dipyridamole and amphotericin B were synergistic in their cytotoxic action in rat hepatoma cells and human colon cancer cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Amphotericin B↗
PubMed1987

Biological membrane modeling with a liquid/liquid interface. Probing mobility and environment with total internal reflection excited fluorescence.

Total internal reflection of exciting light, in combination with fluorescence intensity and polarization measurements, was used to selectively study fluorescent compounds adsorbed to the interface region between two immiscible liquids. A fluorometer was constructed which provided excitation at variable angles of incidence and allowed sensitive detection of polarized fluorescence emitted from the interface. The compound 4,4'-bis-1-phenylamino-8-naphthalenesulfonate (bis-ANS) was examined at a decalin/water interface and was found to possess remarkable affinity for the interface region with the bulk of the adsorbed molecule residing in the decalin phase. The adsorbed fluorophore displayed an apparent hindered rotation in the plane of the interface with a rotational diffusion coefficient 3- to 12-fold lower than that expected for bis-ANS in solution. While other dyes examined were not found to be significantly surface active, the addition of cationic surfactant sufficed to induce adsorption of the anionic fluorophore 1-aminonaphthalene-3,6,8-trisulfonic acid. This fluoropore was found to reside in an aqueous environment when bound to the interface, and it also exhibited hindered rotation in the plane of the interface. As the concentrations of the dyes were increased, both adsorbed dyes exhibited polarization reductions consistent with excitation energy transfer. Adsorption of bis-ANS was reversed by addition of bovine serum albumin. The membrane protein cytochrome b5 was found not to bind at the decalin/water interface, indicating that interaction with lipid is required for its adherence to biological membranes.

Anilino Naphthalenesulfonates↗
PubMed1987

Abrupt transitions in physics and biophysics: van der Waals revisited.

An iteration procedure that relates pressure and volume changes in the condensation of a gas by means of two independent relations of the volume and the effective pressure predicts abrupt volume transitions similar to those experimentally observed. Similar abrupt transitions are predicted for a molecular association in which the association free energy is dependent upon the extent of reaction. The pressure, or the concentration, at which the abrupt transition occurs depends upon the volume, or the extent of reaction, used to initiate the iteration procedure and selection of the transition that corresponds to the equilibrium requires additional conditions. For the gas condensation, assumption of the symmetry of the effects of the pressure fluctuations at equilibrium gives results that coincide with those obtained by application of the Maxwell rule. From these observations it is concluded that abrupt transitions arise naturally when independent conditions cannot be simultaneously satisfied.

Journal Article↗
PubMed1987

Laser-induced fusion of mammalian cells and plant protoplasts.

An ultraviolet-laser microbeam was shown to be suitable for inducing fusion of individually selected plant protoplasts or of B-lymphocytes with myeloma cells. The fusion took place in normal culture medium and the fusogenic condition perturbed the cells only for a fraction of a millisecond. Without manipulating the cell culture except for exposing the cells to laser light, fusion products between preselected individual pairs may be produced.

Animals↗
PubMed1987

[Significance of Yersinia enterocolitica and thermophilic Campylobacter for water hygiene].

The taxonomy of Yersinia enterocolitica as well as their classification methods are still unreliable with respect to their pathogenicity. Therefore, a basis of evaluation was established by using extended biochemical tests (API-20-E, API-50-CH) and electrophoretic methods for identifying strains from human, food and water sources. All strains show great inhomogenicity, which was higher for non-human strains than for those isolated from clinical specimens. Thermophilic Campylobacters are especially prevalent in wild living fowl thus being a potential risk for surface water contamination. The results of the study show that high colony counts were found only during winter, whereas in summer the concentration lay below the infective dose. Furthermore, thermophilic Campylobacters were isolated only from samples that contained a higher number of fecal indicator organisms.

Bacteriological Techniques↗
PubMed1987

Atherosclerosis of the vessels in the ligamentum teres. Optical and electron microscopy findings in elderly patients with femoral neck fractures.

The ligamentum teres was studied in 20 subjects, aged from 64 to 83 years, with fractures of the femoral neck treated by prosthetic replacement during 1985. The arterioles were examined under a stereoscopic dissection microscope; they were further studied by optical and electron microscopy. Almost complete occlusion by typical proliferative atherosclerotic changes was a constant finding, thereby cutting off any significant vascular supply to the femoral head.

Aged↗
PubMed1987

Thoracic peridural block in experimental endotoxin shock.

The influence of thoracic peridural block (PDB) on the metabolic and hemodynamic changes in endotoxin shock were investigated in rabbits. During the first 6 h of endotoxin shock, sensomotoric and sympathetic blockade distal to spinal segment T4 was achieved by intermittent administration of bupivacaine into a thoracic peridural catheter. The increase of plasma glucose, lactate, and free glycerol 2 h after endotoxin (50 micrograms/kg) administration was prevented by PDB. Animals with PDB had an accelerated clearance of glucose as indicated by a shorter plasma half-life of intravenously injected glucose (0.33 g/kg) 1 h after endotoxin administration. Hemodynamic parameters were measured during the first 210 min after endotoxin application. Compared with controls, PDB reduced mean arterial pressure and total peripheral resistance. PDB did not affect the initial increase of right ventricular pressure or the progressive decrease in O2 consumption and cardiac output after the endotoxin injection. The mortality at 24 h was not significantly reduced by the PDB (controls, n = 22: 68%; PDB, n = 21: 57%). The results demonstrate that thoracic PDB effectively blocks the sympathetic response in endotoxin shock. Hence, PDB causes peripheral vasodilatation, and, moreover, the metabolic data are consistent with an inhibition of the reactive glycogenolytic and lipolytic responses in shock. Although PDB altered the metabolic disturbances caused by endotoxin shock, mortality was not significantly affected.

Animals↗