PubMed Health⌕ Search

Biomedical subjects

M Widmann

Publications and source records attributed to M Widmann.

14 recordsLinked to original sources
PubMed2000

Comparison of folding rates of homologous prokaryotic and eukaryotic proteins.

The rate of polypeptide chain elongation is up to one order of magnitude faster in prokaryotic cells than in eukaryotes. Here we report that the rates of in vitro refolding of orthologous prokaryotic and eukaryotic proteins correlate with their differential rates of biosynthesis. The mitochondrial and cytosolic aspartate aminotransferases of chicken and aspartate aminotransferase of Escherichia coli show pairwise sequence identities of 41-48% and nearly identical three-dimensional structures. Nevertheless, the prokaryotic enzyme refolded 6 times faster (at 25 degrees C) than the eukaryotic isoenzymes after denaturation in 6 m guanidine hydrochloride. Prokaryotic malate dehydrogenase and lactate dehydrogenase also renatured faster than their orthologous eukaryotic counterparts, suggesting that evolutionary pressure has adapted the rate of folding to the rate of elongation of polypeptide chains.

Aspartate Aminotransferases↗
PubMed1999

[Crisis and decline of bath houses].

For centuries bath-houses and barber-surgeons formed such an integral part of public life that one is mystified by their vanishing from modern view with hardly any trace left. Previous authors have offered a variety of reasons for this disappearance: the bath-houses' notorious reputation, developing fuel-shortage, the "new" fashion of taking the waters and the outbreak of previously unknown contagious diseases are among those mentioned most frequently. While these factors may be valid reasons for a crisis afflicting the "hot-houses" they would hardly explain why fate overtook the barber-surgeons' entire trade. Judging from the sources available one cannot help but feel that the philosophers of the Enlightenment were largely responsible for such a dramatic change of society. Sceptical philosophy discarded the wisdom of the ancient medical authorities replacing traditional steam-bathing with "modern" cold-bathing. Society itself was subject to equally revolutionary changes: the local masters of the trade had to make room for surgeons educated at medical schools setting the stage for a new reality which has become "normal" to us.

Balneology↗
PubMed1998

Secondary structure of bacteriorhodopsin fragments. External sequence constraints specify the conformation of transmembrane helices.

The secondary structure of bacteriorhodopsin polypeptides comprising two (AB, CD, DE, FG), three (AC, CE, EG), four (AD, DG), or five (AE, CG) of the seven transmembrane segments has been analyzed by circular dichroism spectroscopy. A comparison of the alpha-helix content with that predicted from the high resolution structure of the native protein revealed that the N-terminal AB, AC, AD, and AE fragments and the C-terminal CG fragment are completely refolded in the presence of mixed phospholipid micelles. In contrast, the DG, EG, FG, CD, CE, and DE fragments did not form alpha-helices of the expected lengths at pH 6. Each of the latter fragments displayed, however, an increased helicity upon lowering the pH to 4. Fluorescence measurements with the CD and FG fragments suggest that this helix formation occurs within transmembrane segments C and G, respectively, and thus is likely to originate from the protonation of carboxyl residues that participate in proton translocation. The partial misfolding at neutral pH observed for the shorter fragments from the central and C-terminal part of bacteriorhodopsin indicates that the conformation of some transmembrane segments is specified by interactions with neighboring helices in the assembled structure. Moreover, the data demonstrate that two stable helices at the N terminus of a multihelical membrane protein are sufficient as a folding template to induce a native conformation to the following transmembrane domains.

Amino Acid Sequence↗
PubMed1997

Glucocorticoids enhance oxidative stress-induced cell death in hippocampal neurons in vitro.

In patients with Alzheimer's disease, hippocampal cells are among the first neuronal cells of the brain to degenerate. Both rat primary hippocampal neurons and cells of the clonal mouse hippocampal cell line HT22 express endogenous functional glucocorticoid receptors (GRs), as shown by transient transfection of cells with a luciferase reporter plasmid containing GR-responsive elements. The influence of activated GRs on oxidative stress-induced neuronal cell death in vitro was investigated employing these hippocampal model systems. Two oxidative stressors were investigated, the free radical-inducing Alzheimer's disease-associated amyloid beta-protein, which is toxic to hippocampal neurons, and the excitatory amino acid glutamate, which induces oxidative cell death in HT22 cells via an increase in intracellular peroxides. Cellular viability was assessed with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide test and trypan exclusion staining, followed by microscopical cell counting. Glucocorticoids strongly increased the vulnerability of the hippocampal cells to amyloid beta-protein and glutamate. This increase could be blocked by the specific GR antagonist RU486. Our data suggest that changes in hippocampal GR homeostasis and regulation may render hippocampal neurons more vulnerable to oxidative stress-induced neuronal degeneration.

Alzheimer Disease↗
PubMed1997

Neuroprotection against oxidative stress by estrogens: structure-activity relationship.

Oxidative stress-induced neuronal cell death has been implicated in different neurological disorders and neurodegenerative diseases; one such ailment is Alzheimer's disease. Using the Alzheimer's disease-associated amyloid beta protein, glutamate, hydrogen peroxide, and buthionine sulfoximine, we investigated the neuroprotective potential of estrogen against oxidative stress-induced cell death. We show that 17-beta-estradiol, its nonestrogenic stereoisomer, 17-alpha-estradiol, and some estradiol derivatives can prevent intracellular peroxide accumulation and, ultimately, the degeneration of primary neurons, clonal hippocampal cells, and cells in organotypic hippocampal slices. The neuroprotective antioxidant activity of estrogens is dependent on the presence of the hydroxyl group in the C3 position on the A ring of the steroid molecule but is independent of an activation of estrogen receptors.

Amyloid beta-Peptides↗
PubMed1996

Melatonin prevents oxidative stress-induced cell death in hippocampal cells.

The pineal hormone melatonin has been suggested to be a very effective antioxidant in the brain. Oxidative stress may play a role in certain neuropathological conditions and the hippocampus is an early target of neurodegeneration. Using cells of the clonal hippocampal cell line HT22 and organotypic hippocampal rat brain slice cultures, we investigated a possible protective role of melatonin against oxidative stress-induced hippocampal cell death. Glutamate alone induced oxidative apoptotic cell death in HT22 cells as detected with Hoechst staining and DNA fragmentation analysis. Preincubation with 1 mM melatonin protected HT22 cells against glutamate-induced cell death and protected organotypic hippocampal slices against H2O2-induced cell death. These findings suggest that this neurohormone may be useful in the prevention of neurodegenerative diseases.

Animals↗
PubMed1996

Oxidative stress-resistant cells are protected against haloperidol toxicity.

The neuroleptic drug haloperidol is cytotoxic to cells of different origin in high doses. The mechanism of haloperidol toxicity may involve oxidative stress resulting in necrosis. In the present study, we show that rat pheochromocytoma PC12 cell clones which were selected for resistance to the toxicity of the oxidative stressor amyloid beta-protein (A beta), were also resistant to haloperidol toxicity. This data strongly supports the causative involvement of free radicals in haloperidol-induced cell death.

Animals↗
PubMed1995

Differential effects of molecular chaperones on refolding of homologous proteins.

Three homologous aspartate aminotransferases with virtually identical spatial structures and pairwise amino acid sequence identities of > 40% differ markedly with respect to the yield of renaturation upon dilution from 6 M guanidine hydrochloride (mitochondrial << cytosolic < Escherichia coli). The enzymes also respond differently to molecular chaperones. GroEL/GroES, the Hsp60 homolog of E. coli, increased considerably the yield of renaturation of mitochondrial aspartate aminotransferase and to a lesser extent that of its cytosolic counterpart, but not that of the E. coli enzyme. DnaK/DnaJ/GrpE, the Hsp70 system of E. coli, also increased the yield of renaturation of mitochondrial aspartate aminotransferase. Apparently, specific features in the amino acid sequence or the folding pathway which are independent of the final secondary and tertiary structure determine the interactions of the folding proteins with the chaperone systems.

Animals↗
PubMed1995

17-beta estradiol protects neurons from oxidative stress-induced cell death in vitro.

The potential antioxidant activity of 17-beta estradiol and other steroid hormones in neuronal cells was investigated by studying oxidative stress-induced cell death caused by the neurotoxins amyloid beta protein, hydrogen peroxide and glutamate in the clonal mouse hippocampal cell line HT22. Preincubation of the cells with 10(-5) M 17-beta estradiol prior to addition of the neurotoxins prevented oxidative stress-induced cell damage and ultimately cell death, as detected with cell viability (MTT) and cell lysis (trypan blue exclusion/cell counting; propidium iodide staining) assays. At the DNA level, 17-beta estradiol blocked the DNA degradation caused by glutamate. Other steroid hormones, such as progesterone, aldosterone, corticosterone and the steroid precursor cholesterol, did not protect the cells. The neuronal protection afforded by 17-beta estradiol was estrogen receptor-independent. These data demonstrate a potent neuroprotective activity of the antioxidant 17-beta estradiol, which may have implications for the prevention and treatment of Alzheimer's disease.

Aldosterone↗
PubMed1995

[Inadvertant suture fixation of a Swan-Ganz catheter to the pulmonary artery following heart surgery].

We report a patient undergoing redo cardiac surgery for combined replacement of the aortic and mitral valves. During the course of the operation, a Swan-Ganz catheter - positioned preoperatively - was accidentally fixed to the wall of the pulmonary artery. As this did not interfere with cardiac output measurement or the pulmonary artery pressure wave form, the fixation was not noticed until an attempt was made to remove the catheter. Fluoroscopy revealed both the catheter's immobility and the location of the suture fixation. The patient required a sternotomy to remove the catheter. In order to avoid this complication, the indications for pulmonary artery catheters during cardiac surgery should be carefully considered. If catheters are inserted, their mobility should by all means be ensured before the chest is closed.

Aged↗
PubMed1993

The DNA-binding properties of an artificial 42-residue polypeptide derived from a natural repressor.

Bacteriophage 434 repressor recognizes the operator sequences ACAAG and ACAAT. As the same or similar sequences occur in the enhancer region of HIV-1, 434 repressor was a potential HIV enhancer-binding protein. We found that the interaction of the DNA-binding domain of 434 repressor with a 57-bp HIV enhancer DNA was very weak whereas a 42-residue construct, comprising the recognition helix and four copies of a positively charged segment of the repressor, bound strongly. The results of footprint and cell-free in vitro transcription studies showed that the 42-residue peptide bound preferably to the enhancer region of HIV-1 and acted as an artificial repressor. Replacement of an essential glutamine of the recognition helix by glutamic acid resulted in a partial shift of the sequence specificity of the 42-residue peptide.

Amino Acid Sequence↗
PubMed1990

Pulmonary capillary pressure and gas exchange after E. coli bacteremia in pigs.

In 9 Goettingen minipigs we studied the effect of E. coli bacteremia on effective pulmonary capillary pressure and the longitudinal distribution of pulmonary vascular resistance. Precapillary pressure gradient (dPa) was calculated as the difference between mean pulmonary artery pressure (MPP) and effective pulmonary capillary pressure (Pc) (dPa = MPP-Pc), postcapillary pressure gradient (dPv) as the difference between Pc and left atrial pressure (dPv = Pc-LAP). The disturbance of pulmonary gas exchange was quantified by the AaDO2 quotient 1-PaO2/PAO2. Live E. coli infusion resulted in hypodynamic circulatory failure. Cardiac index fell from 3.7 +/- 0.81 . min-1.m-2 to 2.2 +/- 0.71 .min-1.m-2 after bacteremia lasting for 3.5 h. Simultaneously venous pulmonary vascular resistance rose from 25% of total pulmonary vascular resistance before to 32% after 3.5 h bacteremia, thus raising Pc from 11 mmHg to 16 mmHg. The degree of respiratory insufficiency was correlated with changes of MPP, dPa and dPv: 1-PaO2/PAO2 = 0.2 + 0.035.dPv (r = 0.829). Our results show, that the longitudinal distribution of pulmonary vascular resistance changes during septicemia, thus raising Pc. This may be an important factor in the genesis of septic pulmonary failure.

Animals↗
PubMed1985

Evaluation of a QRS scoring system for estimating myocardial infarct size. V. Specificity and method of application of the complete system.

The specificity of a previously developed 57-criteria/32-point QRS scoring system for estimating myocardial infarct (MI) size is evaluated in an extensive control population and the method of application of this system for determining a QRS score from a standard 12-lead electrocardiogram is described. Points are accumulated from Q- and R-wave durations, R- and S-wave amplitudes, R/Q- or R/S-amplitude ratios and the presence of R-wave notching, with each point representing approximately 3% of the left ventricle. The subjects were selected because of the minimal likelihood of their having had myocardial infarcts or other sources of QRS modification. There were 500 consecutively selected normal Caucasian subjects, aged 20 to 69 years, with 50 women and 50 men in each of the 5 decades. Specificity for the 57 individual criteria ranged from 89 to 100%. Fifty-one criteria met the required standard of at least 95% specificity; of the 6 that failed, 3 were successfully modified to achieve this standard and 3 were eliminated. In the resultant 54-criteria/32-point complete system, the total population, as well as both women and men, required more than 3 points to attain at least 95% specificity. Subjects in each of the 5 decades met the specificity standard either at or below the level of more than 3 points. The point score at which 95% or greater specificity was attained for the 10 age/sex subsets varied.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗