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Biomedical subjects

J Fischer

Publications and source records attributed to J Fischer.

At least 541 records · Page 30Linked to original sources
PubMed1978

Enzymatic attack on immobilized substrates. 2. Diffusional limitations in the alpha-chymotrypsin-catalyzed hydrolysis of polyacrylamide-bound l-phenylalanine 4-nitroanilide.

1. The chymotrypsin-catalyzed hydrolysis of polyacrylamide-bound L-phenylalanine 4-nitroanilide was studied. As a spacer, one or two 6-aminohexanoyl residues were inserted between the matrix and ligand. 2. In the course of the enzymatic hydrolysis of polyacrylamide-bound substrates, enzyme adsorption by the gel substrates was observed. A quasi equilibrium of enzyme partitioning was reached after approximately 20-min incubation time. The enzyme adsorption could be described by the Langmuir adsorption isotherm. 3. The substrates attached via spacers to the matrix were completely hydrolyzed. 4. The initial course of the product vs time curves, as well as the dependence of the initial hydrolysis rates on enzyme concentration or substrate concentration, have been interpreted by the Nernst reaction theory. From the results obtained it has been concluded that the inital rate of the hydrolysis of polyacrylamide-bound L-phenylalanine 4-nitroanilide depends on the velocity of enzyme diffusion into the matrix.

Acrylamides↗
PubMed1978

Studies on the time course and rate-limiting steps in the activation of adenylate cyclase in rat liver by cholera toxin.

Cholera toxin stimulates adenylate cyclase in rat liver after intravenous injection. The stimulation follows a short latent period of 10min, and maximum stimulation was attained at 120min. Half-maximal stimulation was achieved at 35min. In contrast with this lengthy time course in the intact cell, adenylate cyclase in broken-cell preparations of rat liver in vitro were maximally stimulated by cholera toxin (in the presence of NAD+) in 20min with half-maximal stimulation in 8min. Binding of cholera toxin to cell membranes by the B subunits is followed by translocation of the A subunit into the cell or cell membrane, and separation of the A1 polypeptide chain from the A2 chain by disulphide-bond reduction, and finally activation of adenylate cyclase by the A1 chain and NAD+. As the binding of cholera toxin is rapid, two possible rate-limiting steps could be the determinants of the long time course of action. These are translocation of the A1 chain from the outside of the cell membrane to its site of action (this includes the time required for separation from the whole toxin) or the availability of NAD+ for activation. When NAD+ concentrations in rat liver were elevated 4-fold, by the administration of nicotinamide, no change in the rate of activation of adenylate cyclase by cholera toxin was observed. Thus the intracellular concentration of NAD+ is not rate-limiting and the major rate-limiting determinant in intact cells must be between the time of toxin binding to the cell membrane and the appearance of subunit A1 at the enzyme site.

Adenylyl Cyclases↗
PubMed1978

Orientation of acidic polysaccharides and rhodopsin-oligosaccharides in frog retinal rod outer segments.

Using topo-optical staining reactions, the presence and molecular order of three structural components of outer segments of frog retina were studied. These components included (1) an acidic polysaccharide texture, (2) free aldehyde groups which arise during formalin fixation and (3) the oligosaccharide chains of rhodopsin. Quantitative measurements of the dye binding and birefringence effects arising from the individual structural components in rod outer segments were made. Results indicated that all three structural components had a rather well-defined orientation within the ROS. The spherulites phagocytized from the apical ends of ROSs by the pigment epithelium also demonstrate preferred orientation of the three structural components investigated.

Aldehydes↗
PubMed1978

Development of perifocal edema in experimental epilepsy induced by cobalt-gelatin.

Two blood-borne tracers, Evans-blue albumin (EBA) and colloidal-iron (Ferrlecit) were applied to visualize the development of perifocal edema in experimental epilepsy induced by cobalt-gelatin (Co-gelatin). This model is known to produce central necrosis with gliomesenchymal scar and peripheral transitory zone in the brain cortex. Characteristic red fluorescence of EBA was detected diffusely in the necrotic area surrounding the Co-gelatin implant and EBA labelled individual neurons reflecting cell membrane injury in the transitory zone. The colloidal iron tracer was localized mainly in the gliomesenchymal scar. It is proposed that neurons with altered membrane permeability to EBA in the transitory zone may play a role in the genesis of epileptic spike activity. The marked labelling of the gliomesenchymal scar by colloidal-iron indicates furthermore that this newly vascularized tissue with leaky capillaries may be a source of perifocal edema.

Animals↗
PubMed1978

Metastasizing atypical fibroxanthoma. Coexistence with chronic lymphocytic leukemia.

Atypical fibroxanthoma (AFX) is one of a group of cutaneous lesions with a malignant histological appearance but a generally benign clinical course. A 79-year-old white man had AFX of the cheek that recurred and metastasized to buccal and cervical lymph nodes three months after initial diagnosis. When careful physical and and laboratory examinations were done, the patient was found to have concomitant chronic lymphatic leukemia, "null cell" type. In view of the low incidence of metastasizing AFX and the increased occurrence of tumors in patients with lymphomatous disorders, an important association is suggested. Before establishing the prognosis for patients with pseudomalignancies of the skin, an evaluation of their general health and immunological status should be made.

Aged↗
PubMed1978

Na-G-penicillin penetration into rat cerebral cortex and formation of an epileptic focus.

Fluorescein isothiocyanate-labelled Na-G-penicillin was applied to the intact dura of 11 rats and the cortical layers were determined to which this epileptogenic substance must penetrate for electrophysiologically demonstrable focal activity to be induced. In 10 animals labelled penicillin was demonstrated in cortical layers I--III and in one animal in layers I and II. This concurs with the results obtained in 12 other animals in which activity was recorded from three depths of the cerebral cortex with semimicroelectrodes.

Animals↗
PubMed1978

D(-)-N-Methylglucamine buffer for pH 8.5 to 10.5.

A new amine buffer for the pH range 8.5 to 10.5 based on D(-)-N-methylglucamine and its hydrochloride is described. Important physical and chemical constants characterizing this buffer system have been determined: thermodynamic pKa = 9.52 (25 degrees C), buffer capacity = 0.055, dilution value pH 1/2 = -0.02, temperature coefficient dpKa/dT = 0.023, the heat of ionization delta H degrees = 36.93 kj mol-1. D(-)-N-Methylglucamine, which is available in highly purified form, is highly soluble in water. Thus one can prepare either buffer solutions or stable solid mixtures when combined with D(-)-N-methylglucaminium chloride. D(-)-N-Methylglucamine buffers are suitable for both biochemistry and pH control.

Buffers↗
PubMed1978

The influence of charged matrix surfaces on the thermostabilizing effect of calcium ions on immobilized fungal alpha-amylase.

The stabilizing effect of calcium ions on fungal alpha-amylase (EC 3.2.1.1) immobilized on a polystyrene anion exchanger (P+ amylase) was investigated and compared to the behaviour of soluble amylase. Moreover, gamma-(1,4-benzoquinone-2-yl)-aminopropyl silica-amylase (Si(n) amylase) as a conjugate with weakly basic amino groups and gamma-succinamidopropyl silica amylase (Si- amylase) as a conjugate with free carboxyl groups were applied for comparison. Depending on the calcium ion concentration the immobilized amylases showed a lower thermal stability than the soluble enzyme. The reduced stability was attributed to matrix effects in the microenvironment of the immobilized amylases and the calcium ion concentration in the carrier phase, which was changed in comparison with the external solution. Contrary to the non-measurable matrix effects in the microenvironment, altered calcium ion concentrations in the carrier phase of the polystyrene anion exchanger (P+) and gamma-succinamidopropyl silica (Si-) could be detected. With increasing calcium ion concentration a greater decrease of activity was observed for the soluble amylase than for the immobilized enzymes. The thermal stability of soluble amylase and P+ amylase was studied in dependence on pH. In the acidic pH-range P+ amylase indicated a higher thermal stability than the soluble enzyme in the presence of Ca2+ as well as in the absence of Ca2+. Contrary to soluble amylase the stabilizing effect of calcium ions on P+ amylase begins already at pH 3.5. Kinetic investigations for thermal inactivation were performed on soluble amylase and P+ amylase in the presence and absence of Ca2+ in the temperature range between 44--60 degrees C. Thermal inactivation proceeded by first order reactions. The inactivation rate constants kin served as a measure of thermal stability for discussing the stabilizing effect by Ca2+ depending on the temperature. The activation energies of inactivation EA were determined from the Arrhenius-plot of the inactivation rate constants.

Amylases↗
PubMed1977

[Frequent cases of agranulocytosis due to clozapin (leponex) in eastern Switzerland].

Two personally observed cases of severe agranulocytosis within 3 months, one of them fatal, could be attributed to the new dibenzodiazepine derivative Clozapine (Leponex). Clozapine, a very effective neuroleptic for the treatment of acute and chronic schizophrenia, has been found before to induce agranulocytosis of the metabolic type, as phenothiazines are known to do. An inquiry in al Swiss medical departments and mental hospitals revealed a total of 20 cases of Clozapine induced agranulocytosis in some 50% of institutions responding. 9 of these were observed in Eastern Switzerland. This time-space clustering recalls the "finnish epidemic" of 1975 in Southern Finland. Possible explanations for this phenomenon are discussed. Calculations of the incidence suggest a higher rate of agranulocytosis induced by Clozapine than has been assumed for the phenothiazines. Clozapine should therefore be restricted to schizophrenic patients and initially (6 weeks) be given only on a stationary basis under regular blood controls.

Adult↗