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Biomedical subjects

A Birk

Publications and source records attributed to A Birk.

13 recordsLinked to original sources
PubMed1999

Heme-solvent coupling: a Mössbauer study of myoglobin in sucrose.

The Mössbauer effect of 57Fe-enriched samples was used to investigate the coupling of 80% sucrose/water, a protein-stabilizing solvent, to vibrational and diffusive modes of the heme iron of CO-myoglobin. For comparison we also determined the Mössbauer spectra of K4 57Fe (CN)6 (potassium ferrocyanide, PFC), where the iron is fully exposed in the same solvent. The temperature dependence of the Mössbauer parameters derived for the two samples proved to be remarkably similar, indicative of a strong coupling of the main heme displacements to the viscoelastic relaxation of the solvent. We show that CO escape out of the heme pocket couples to the same type of fluctuations, whereas intramolecular bond formation involves solvent-decoupled heme deformation modes that are less prominent in the Mössbauer spectrum. With respect to other solvents, however, sucrose shows a reduced viscosity effect on heme displacements and the kinetics of ligand binding due to preferential hydration of the protein. This result confirms thermodynamic predictions of the stabilizing action of sucrose by a dynamic method.

Animals↗
PubMed1996

Leg oedema protection from a buckwheat herb tea in patients with chronic venous insufficiency: a single-centre, randomised, double-blind, placebo-controlled clinical trial.

OBJECTIVES: The efficacy of a buckwheat herb tea was determined in patients with chronic venous insufficiency (CVI) in a single-centre, randomised, double-blind, placebo-controlled clinical trial. METHODS: Sixty-seven male and female patients (22-74 years) with CVI were randomly divided into two groups after a 2-week run-in period. They received either buckwheat herb tea (Fagopyrum esculentum) or a placebo tea for a period of 3 months. The main outcome measure was the lower leg volume determined by ultrasound. Subjective symptoms were assessed by a clinical symptom score system. The femoral vein diameters were measured by B-scan sonography. In a subgroup of patients capillary permeability was determined by cutaneous fluorescence angiography. RESULTS: Although the mean partial leg volume did not change in the treatment group (from 2041 to 2073 ml), it increased in the placebo group by 110 ml (from 1972 to 2082 ml) according to intent to treat. The difference between the groups was significant. The subjective clinical symptoms were significantly reduced in both groups. The mean diameters of the femoral veins were reduced and capillary permeability was improved, but neither change was statistically significant. No drug-related adverse effects were observed. CONCLUSION: CVI is a very placebo-sensitive condition. The treatment with buckwheat herb tea is safe and could have a favourable influence on patients with CVI such that further oedema development is prevented.

Adult↗
PubMed1995

Sequence and structure requirements for Drosophila tRNA 5'- and 3'-end processing.

Eukaryotic tRNAs are processed at their 5'- and 3'- ends by endonucleases RNase P and 3'-tRNase, respectively. We have prepared substrates for both enzymes, separated the activities from a Drosophila extract, and designed variant tRNAs to assess the effects of sequence and structure on processing. Mutations affect these reactions in similar ways; thus, RNase P and 3'-tRNase probably require similar substrate structures to maintain the catalytic fit. RNase P is more sensitive to substrate substitutions than 3'-tRNase. In three of the four stems, one substitution prevents both processing reactions while the opposite one has less effect; anticodon stem substitutions hardly affect processing, and double substitution intended to restore base pairing also restore processing to the wild type rate. Structure probing suggests that tRNA misfolding sometimes coincides with reduced processing. In other cases, processing inhibition probably results from specific unfavorable stem appositions leading to local helix deformation. A single T loop substitution disrupts the tertiary D-T loop interaction and reduces processing. We have thus begun mapping tRNA processing determinants on the global, local, and tertiary structure levels.

Animals↗
PubMed1994

Determination of 2-5A synthetase and 2-5A phosphodiesterase in neuroblastoma cells by analytical capillary isotachophoresis: effects of cytokines and comparison with radioenzymatic methods.

2-5A Synthetase and 2-5A phosphodiesterase were determined by analytical capillary isotachophoresis in comparison to radioenzymatic methods. By means of isotachophoretic analysis, a frequently used radioenzymatic 2-5A synthetase assay was optimized and the results of both assays were compared. Using the isotachophoretic assay the influence of interferon-related cytokines (tumor necrosis factor-alpha and interleukin-2) on 2-5A synthetase induction in neuroblastoma cells was estimated. In contrast to mononuclear blood cells, the tumor necrosis factor induced 2-5A synthetase in these cells. 2-5A Phosphodiesterase was determined using an isotachophoretic assay and a radioenzymatic method. Degradation of A2'p5'A2'p5'A (trimeric form of 2-5A core) was measured by isotachophoresis whereas degradation of a mixture of phosphorus-32 labeled 2-5A cores was registered by radioenzymatic assay. Activity of 2-5A phosphodiesterase was only insignificantly enhanced by interferon in mononuclear blood and neuroblastoma cells. In contrast to the radioenzymatic assays, an accurate determination of 2-5A synthetase as well as of 2-5A phosphodiesterase is possible using the isotachophoretic method because the reactions are followed by measuring the substrates ATP and A2'p5'A2'p5'A, respectively.

2',5'-Oligoadenylate Synthetase↗
PubMed1994

Hypervolemic hemodilution with or without venesection in peripheral arterial occlusive disease stage II.

Patients with peripheral arterial occlusive disease (PAOD) and marked atherosclerosis often present concomitant diseases like coronary heart disease, cerebral circulatory disorders or arterial hypertension. Thus, the extent of hypervolemia is limited in case of an infusion treatment without venesection. Therefore, it was tested whether a hypervolemic hemodilution without venesection is superior to a dilution with venesection in multimorbid patients suffering from PAOD stage II. The colloidal iso-molar solution used was Haes 200/0.5 6%. Both forms of hemodilution were significantly superior compared to a control group well hydrated with cristalloid saline solution; all groups practised walking exercise twice a week over a period of one hour. However, hypervolemic hemodilution without venesection was only slightly better than the dilution with venesection. The walking distance in the group without venesection increased by 68.6 m (36.7%) in the group without venesection, by 59.0 (30.4%) in the group with venesection and by 33.6 m (20.1%) in the control group. The results show that the decision to perform a hyperor isovolemic hemodilution should depend on the volume tolerance of each patient.

Adult↗
PubMed1993

Poly(U)-binding protein inhibits Drosophila pre-5 S RNA 3'-exonuclease digestion.

A approximately 50-kDa protein binds specifically to the 3' terminus of 135-nucleotide Drosophila pre-5 S RNA. Unlabeled poly(U) competes out protein binding and stimulates the activity of a 3'-exonuclease, which eventually degrades the substrate to 120 nucleotides, the size of mature 5 S RNA. In its RNA binding and UV cross-linking properties, the endogenous poly(U)-binding protein resembles human La, an autoantigen that binds the U > 3 3' ends of vertebrate RNA polymerase III primary transcripts. This protein appears to inhibit a 3' exonuclease and could protect 5 S RNA for faithful processing and transport.

Animals↗
PubMed1993

Effects of garlic coated tablets in peripheral arterial occlusive disease.

For the first time, a weak clinical efficacy of a 12-week therapy with garlic powder (daily dose, 800 mg) is demonstrated in patients with peripheral arterial occlusive disease stage II. The increase in walking distance in the verum group by 46 m (from 161.0 +/- 65.1 to 207.1 +/- 85.0 m) was significantly higher (P < 0.05) than in the placebo group (by 31 m, from 172.0 +/- 60.9 to 203.1 +/- 72.8). Both groups received physical therapy twice a week. The diastolic blood pressure, spontaneous thrombocyte aggregation, plasma viscosity, and cholesterol concentration also decreased significantly. Body weight was maintained. It is quite interesting that the garlic-specific increase in walking distance did not appear to occur until the 5th week of treatment, connected with a simultaneous decrease in spontaneous thrombocyte aggregation. Therefore, garlic may be an appropriate agent especially for the long-term treatment of an incipient intermittent claudication.

Adult↗
PubMed1991

[Hyper- or isovolemic hemodilution in patients with stage II peripheral arterial occlusive disease].

The influence of hyper- and isovolaemic hemodilution using HES 200/0.5 6% (HES steril, Fresenius AG) on pain-free walking distance in patients with peripheral arterial occlusive disease stage II according to Fontaine was tested in a randomised investigation involving three groups. The increase in pain-free walking distance was significant both in the hypervolaemic and isovolaemic hemodilution group. The increase in both dilution groups did not differ but compared to a control group (infusion of Ringer lactate) it was significantly higher. Considerable changes concerning rheological parameters (decrease in haematocrit and plasma viscosity) were observed after isovolaemic hemodilution.

Adolescent↗
PubMed1989

[Hemodilution in patients with multiple morbidity and peripheral arterial occlusive disease].

The treatment of multi-morbid patients suffering from peripheral arterial occlusive disease (PAOD) is rendered difficult due to concomitant diseases such as coronary heart disease, chronic obstructive pulmonary affection, arterial hypertension or diabetes mellitus. Haemodilution can be a clinically efficient therapy for some of the concomitant diseases as well. It is, however, necessary to use a weak colloidal solution which has no additional volume effect as an iso-oncotic substance. Hydroxyethyl starch 200/0.5 6% meets all these demands. In a double-blind, placebo-controlled study over a period of 6 weeks a marked and significant increase of almost 40% in painfree walking distance was achieved for 19 of 37 multi-morbid patients with PAOD II by moderate hypervolaemic haemodilution with venesections. Besides the clinical improvement, blood fluidity also increased through a reduction in haematocrit, plasma viscosity, and erythrocyte aggregation.

Adult↗