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M Preuss

Publications and source records attributed to M Preuss.

31 records · Page 2Linked to original sources
PubMed1999

Relationship between Na+-Ca2+-exchanger protein levels and diastolic function of failing human myocardium.

BACKGROUND: In the failing human heart, sarcoplasmic reticulum (SR) calcium handling is impaired, and therefore, calcium elimination and diastolic function may depend on the expression of sarcolemmal Na+-Ca2+ exchanger. METHODS AND RESULTS: Force-frequency relations were studied in ventricular muscle strip preparations from failing human hearts (n=29). Protein levels of Na+-Ca2+ exchanger and SR Ca2+-ATPase were measured in the same hearts. Hearts were divided into 3 groups by discriminant analysis according to the behavior of diastolic function when stimulation rate of muscle strips was increased from 30 to 180 min-1. At 180 compared with 30 min-1, diastolic force was increased by 160%, maximum rate of force decline was decreased by 46%, and relaxation time was unchanged in group III. In contrast, in group I, diastolic force and maximum rate of force decline did not change, and relaxation time decreased by 20%. Na+-Ca2+ exchanger was 66% higher in group I than in group III. Na+-Ca2+ exchanger was inversely correlated with the frequency-dependent rise of diastolic force when stimulation rate was increased (r=-0.74; P<0.001). Compared with nonfailing human hearts (n=6), SR Ca2+-ATPase was decreased and Na+-Ca2+ exchanger unchanged in group III, whereas Na+-Ca2+ exchanger was increased and SR Ca2+-ATPase unchanged in group I. Results with group II hearts were between those of group I and group III hearts. CONCLUSIONS: By discriminating failing human hearts according to their diastolic function, we identified different phenotypes. Disturbed diastolic function occurs in hearts with decreased SR Ca2+-ATPase and unchanged Na+-Ca2+ exchanger, whereas increased expression of the Na+-Ca2+ exchanger is associated with preserved diastolic function.

Adult↗
PubMed1998

Measuring the Contact Angle of Individual Colloidal Particles.

The aim of this study was to measure the contact angles of individual colloidal spheres ( solidus in circle 4.4 µm) and compare it to contact angles obtained on similarly prepared planar surfaces. For this purpose the particles were attached to atomic force microscope cantilevers. Then the force between the particle in aqueous medium and an air bubble was measured versus the distance. From the resulting force curves we obtained contact angles and detachment forces of single particles. Contact angles of gold coated silica particles were adjusted between 20 degrees and 100 degrees by self-assembling monolayers from different mixtures of undecanethiols and omega-hydroxy undecanethiols from solution. In parallel, contact angles on flat gold surfaces prepared in the same way were determined by the sessile drop method. A systematic difference between contact angles measured with particles and on planar surfaces was observed. Results are discussed in terms of line tension of the three-phase contact line. In addition, detachment forces were measured. Detachment forces were slightly higher than predicted from flotation theory. This might be caused by a pinning of the three phase contact line. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Homogeneous Escherichia coli chaperonin 60 induces IL-1 beta and IL-6 gene expression in human monocytes by a mechanism independent of protein conformation.

Escherichia coli chaperonin (cpn) 60 (groEL) is a protein-folding oligomer lacking tryptophan residues that copurifies with tryptophan-containing proteins and peptides. Cpn 60 is a major immunogen in infectious diseases, and evidence suggests that groEL and mycobacterial cpn 60s can induce cytokine synthesis, stimulate cytokine-dependent bone resorption, and up-regulate expression of vascular endothelial cell adhesion molecules. Whether such activities are due to the cpn 60 or to the copurifying/contaminating proteins/peptides has not been determined. Here we report a method for removing the protein contaminants of groEL and demonstrate that this, essentially homogeneous, groEL remains a potent inducer of human monocyte IL-1beta and IL-6 production. Contaminating peptides had no cytokine-inducing activity and did not synergize with purified groEL. The LPS inhibitor polymyxin B and the CD14-neutralizing Ab MY4 had no inhibitory action on groEL demonstrating that activity is not due to LPS contamination. Heating groEL had no effect on its capacity to stimulate human monocytes to secrete IL-6. Proteolysis of groEL with trypsin, sufficient to produce low molecular mass peptides, also had no inhibitory effect. Thus, we conclude that groEL is a potent inducer of monocyte proinflammatory cytokine production, which acts through the binding of nonconformational peptide domains that are conserved after proteolysis. These data suggest that if groEL was released from bacteria it could induce prolonged tissue pathology by virtue of its cytokine-inducing activity and its resistance to proteolytic inhibition of bioactivity.

Antibodies, Monoclonal↗
PubMed1998

Influence of SR Ca(2+)-ATPase and Na(+)-Ca(2+)-exchanger on the force-frequency relation.

The data presented indicate that altered systolic and diastolic function in failing human hearts may result from altered expression of calcium cycling proteins. Decreased systolic force production and inversion of the force-frequency relation seem to be related to reduced protein levels of SR Ca2+ ATPase and/or to increased protein levels of the Na(+)-Ca2+ exchanger resulting in an increased ratio of Na(+)-Ca2+ exchanger to SR Ca2+ ATPase. Impaired diastolic function may result from reduced SR Ca2+ ATPase and is most pronounced in failing hearts with lack of upregulation of the Na(+)-Ca2+ exchanger. Thus, failing hearts with reduced SR Ca2+ ATPase protein levels and unchanged Na(+)-Ca2+ exchanger protein levels exhibit severe impairment of both systolic and diastolic function.

Biomechanical Phenomena↗
PubMed1998

The Escherichia coli chaperonin 60 (groEL) is a potent stimulator of osteoclast formation.

Chaperonins (cpns) are intracellular oligomeric protein complexes that fold and refold proteins in a catalytic manner and aid in the transmembrane transport of cellular proteins. We reported previously that the lipopolysaccharide-free recombinant cpn60 of Escherichia coli (groEL) is able to stimulate the breakdown of murine calvarial bone in culture and showed that such resorption is potently inhibited by an inhibitor of the enzyme cyclo-oxygenase and to a lesser extent by inhibitors of 5-lipoxygenase. In this study, we have investigated the effects of groEL on the resorptive activity and formation of osteoclasts in culture. In low density, osteoclast-containing cultures from neonatal rats incubated for 24 or 96 h on dentine discs, groEL (1-1000 ng/ml) stimulated resorption pit formation up to 4-fold, but this effect was essentially dependent on cell number. Using 12-day cultures of mouse bone marrow to assess osteoclast recruitment, groEL (1-1000 ng/ml) caused a dramatic dose-dependent stimulation of the formation of tartrate-resistant acid phosphatase-positive multinucleated cells and the resorption of the dentine on which bone marrow cells were cultured. Osteoclast formation elicited by groEL was almost completely abolished by indomethacin, an inhibitor of cyclo-oxygenase, but was unaffected by inhibitors of 5-lipoxygenase, suggesting that prostaglandins but not leukotrienes may mediate the action of groEL on osteoclastogenesis. It is possible that bacterial cpn60s such as groEL may play a role in the osteolysis associated with bone infections. Whether endogenous ("self") chaperonins have a role in other bone loss disorders, such as osteoporosis, is an intriguing possibility.

Acid Phosphatase↗
PubMed1997

Calcium handling proteins in the failing human heart.

There is accumulating evidence that disturbed calcium homeostasis may play a key role in the pathophysiology of human heart failure. Because disturbed calcium handling could result from altered protein expression, levels of calcium handling proteins were quantitated by Western Blot analysis in failing and nonfailing human myocardium from hearts with endstage failing dilated or ischemic cardiomyopathy. Protein levels of the sarcoplasmic reticulum calcium release channel (ryanodine receptor) and of calcium storage proteins (calsequestrin and calreticulin) were similar in failing and nonfailing human myocardium. However, proteins involved in calcium removal from the cytosol were significantly altered in the failing human heart: 1) SR-Ca(2+)-ATPase, relevant for removal of calcium from the cytosol into the lumen of the sarcoplasmic reticulum, was decreased; 2) phospholamban, which inhibits the SR-Ca(2+)-ATPase in the basal unphosphorylated state, was slightly decreased; 3) the ratio of SR-Ca(2+)-ATPase to phospholamban was decreased; 4) the sarcolemmal Na(+)-Ca(2+)-exchanger, relevant for transsarcolemmal calcium extrusion was increased in the failing hearts. In summary, altered levels of proteins involved in calcium removal from the cytosol suggest an increase in transsarcolemmal calcium elimination relative to sarcoplasmic reticulum calcium removal. These findings support the concept that reduced function of the sarcoplasmic reticulum to accumulate calcium may reflect a major defect in excitation-contraction coupling in human heart failure.

Calcium↗
PubMed1997

Expression of var genes located within polymorphic subtelomeric domains of Plasmodium falciparum chromosomes.

Plasmodium falciparum var genes encode a diverse family of proteins, located on the surfaces of infected erythrocytes, which are implicated in the pathology of human malaria through antigenic variation and adhesion of infected erythrocytes to the microvasculature. We have constructed a complete representative telomere-to-telomere yeast artificial chromosome (YAC) contig map of the P. falciparum chromosome 8 for studies on the chromosomal organization, distribution, and expression of var genes. Three var gene loci were identified on chromosome 8, two of which map close to the telomeres at either end of the chromosome. Analysis of the previously described chromosome 2 contig map and random P. falciparum telomeric YAC clones revealed that most, if not all, 14 P. falciparum chromosomes contain var genes in a subtelomeric location. Mapping the chromosomal location of var genes expressed in a long-term culture of the P. falciparum isolate Dd2 revealed that four of the five different expressed var genes identified map within subtelomeric locations. Expression of var genes from a chromosomal domain known for frequent rearrangements has important implications for the mechanism of var gene switching and the generation of novel antigenic and adhesive phenotypes.

Animals↗
PubMed1991

[Brain biopsies in HIV-infected patients].

Stereotactic brain biopsies of 25 HIV-seropositive patients (age range between 20 and 56 years, 23 males, 2 females) were retrospectively studied. Biopsy material was examined cytologically, histologically, immunohistochemically and electron microscopically. A definitive diagnosis could be established in 23 cases (92%). Diagnosis included non-Hodgkin's lymphoma (10 cases), toxoplasmosis (10 cases), progressive multifocal leukoencephalopathy (PML) (2 cases) and combined toxoplasmosis and lymphoma (1 case). Two biopsies were non-diagnostic. All lymphomas were B-cell lymphomas of high malignancy including one K1-lymphoma. In six cases, in which autopsy was performed, biopsy diagnosis could be confirmed. In one patient suffering from toxoplasmosis, autopsy demonstrated an additional cytomegalovirus infection. Conventional histology was not sufficiently decisive for toxoplasmosis, for some lymphomas and for PML. Stereotactic brain biopsy appears to be an effective method in the diagnosis of HIV-associated brain lesions.

Adult↗
PubMedDate not supplied

Design of a molecular chaperone-assisted protein folding bioreactor.

Escherichia coli molecular chaperone GroEL and co-chaperone GroES are well known to assist the folding/refolding of a diverse range of substrate proteins. Despite this, there have been relatively few reports of the GroEL/GroES molecular chaperone system being used as a biotechnology tool for protein folding/refolding. In this paper, a solution-phase protein folding bioreactor is described that involves the complete GroEL/GroES system. The main features of this bioreactor are the use of a stirred-cell concentrator fitted with a 100 kDa molecular weight cutoff membrane and an attached buffer reservoir. This bioreactor system was used successfully for assisted-batch refolding of guanidinium chloride (Gu-HCl) unfolded mitochondrial malate dehydrogenase (mMDH). We believe that protein folding bioreactor systems of this type could have wide potential utility for the folding/refolding of unfolded protein substrates.

Animals↗
PubMedDate not supplied

Purification and characterization of a dissimilatory nitrite reductase from the phototrophic bacterium Rhodopseudomonas palustris.

A dissimilatory nitrite reductase from the facultatively phototrophic bacterium, Rhodopseudomonas palustris strain 1a1 was studied. A basic level of the enzyme (10-50 mU/mg protein) was measured in dark, aerated and anaerobic, photosynthetic cultures. A marked derepression of enzyme synthesis occurred under conditions of oxygen limitation (200-300 mU/mg protein). The addition of nitrite (or nitrate) to the culture medium had only a slight effect on the maximal nitrite reductase titer of cells. The enzyme was purified from photosynthetically grown cells by precipitation with ammonium sulfate, gel filtration through Sepharose 6B and repeated chromatography on DE 52-cellulose. As estimated by gel filtration, the nitrite reductase had a molecular weight of about 120 000 +/- 12 000 and yielded only one band (mol. wt. of about 68 000 +/- 7000) in SDS-gel electrophoresis. The isoelectric point of the enzyme was at pH 5.1. Nitric oxide (NO) was identified as the reaction product of nitrite reduction. The enzyme also exhibited cytochrome c-oxidase activity and was active with chemically reduced viologen dyes, FMN and cytochrome c as electron donors. Highly purified nitrite reductase preparations contained 10 mol% of a c-type cytochrome. Trace metal analyses indicated the presence of Cu in the enzyme. Consistent with the detection of Cu was the finding that the Cu-chelator, diethyldithiocarbamate, strongly inhibited the nitrite reductase.

Catalysis↗