Search PubMed⌕ Search

Biomedical subjects

P Lindner

Publications and source records attributed to P Lindner.

At least 19 recordsLinked to original sources
PubMed2005

Shear thinning and orientational ordering of wormlike micelles.

Shear thinning and orientation of cylindrical surfactant and block copolymer micelles was investigated by rheo-SANS (small-angle neutron scattering) experiments. Shear thinning and orientation occur for shear rates (.)gamma tau(dis)>>1, where tau(dis) is the disentanglement time of the micelles. Micelles align in the flow direction with an orientational distribution that can be well described by an Onsager-type distribution function. Over nearly the whole range of concentrations and for all cylindrical micelles investigated, the shear viscosity eta follows a simple eta approximately e(-aS) behavior as a function of the orientational order parameter S with the same prefactor a.

Journal Article↗
PubMed2004

Shear-induced concentration fluctuations and form factor changes in polymer solution in the good-solvent regime.

Small-Angle Scattering from sheared semidilute polymer solution is reported in the good-solvent regime, at variance with former light and neutron measurements in the theta regime. First, concentration fluctuations are observed: the scattering increases noticeably along the flow at low q, but at variance with former results for the theta-solvent regime, no demixing is observed at higher shear. Here, instead, the effects follow a time-temperature superposition and saturate above a Weissenberg number around 5, like the stress which is known to present a plateau for these systems. Using the Zero Average Contrast technique, we have also measured the form factor, which displays the same saturation effect reaching a deformation ratio of the order of 2. These results agree with the Convective Constraint Release models (CCR) elaborated in order to predict the stress effects in the non-Newtonian regime (Marrucci-Ianniruberto) and their extension predicting also the scattering (Likhtman-Milner-McLeish).

Biophysics↗
PubMed2000

Production of recombinant human beta2-microglobulin for scintigraphic diagnosis of amyloidosis in uremia and hemodialysis.

Amyloid of beta2-microglobulin (beta2m) origin can be diagnosed using 131I-radiolabelled-beta2m scintigraphy in patients with uremia and hemodialysis treatment. As the tracer beta2m is isolated from another patient, it carries the common risks, including viral infections such as Hepatitis B, C and HIV, which are associated with human plasma products. In order to exclude these risks we have produced recombinant human beta2m (rhbeta2m) in Escherichia coli. The expression vector pASK40DeltaLbeta2m(His)5 contains a C-terminal (His)5-tag for purification via immobilized metal ion affinity chromatography (IMAC). Size exclusion chromatography on a Superose 12 column represents the second step of purification. The isolated rhbeta2mH5 reacted in an immunochemically identical manner to native human beta2m, and showed a single band of approximately 11.8 kDa in Western blot analysis and revealed a single spot in two-dimensional gel electrophoresis. Mass spectrometry analysis revealed a single peak at the expected molecular mass of 12 415.8 Da. Uniformity was further proven by crystallization and N-terminal amino-acid sequence analysis. The rhbeta2mH5 protein was then produced under conditions that allow the intravenous use in humans. Intraveneously applied indium-111-labelled rhbeta2mH5 was monitored in hemodialysed patients with and without known beta2m-amyloidosis. The tracer was localized specifically to particular areas known to contain amyloid. Thus, this rhbeta2mH5 preparation is suitable for detecting amyloid-containing organs of the beta2m-class in vivo and fulfils the requirements of a tracer for common use. Finally, the use of indium-111 instead of iodine-131 has reduced the radioactive load and resulted in higher resolution.

Amyloidosis↗
PubMed1998

Recombinant homo- and hetero-oligomers of an ultrastable chaperonin from the archaeon Pyrodictium occultum show chaperone activity in vitro.

The archaeon Pyrodictium occultum is one of the most thermophilic organisms presently known. Previous experiments provided support for the significant contribution of a high-molecular-mass protein complex to the extreme thermotolerance of P. occultum. This protein complex, the 'thermosome', is composed of two subunits, alpha and beta, which form a hexadecameric double ring complex. In order to obtain the thermosome in amounts sufficient for structural and functional investigations, we produced the two subunits jointly and separately in Escherichia coli BL21(DE3). In all three cases, we isolated soluble, high-molecular-mass double-ring complexes from E. coli BL21(DE3). On electron micrographs, the recombinant complexes were indistinguishable from each other and from the natural thermosome. To characterize the quaternary structure of the recombinant particles, we used native gel electrophoresis, analytical gel filtration, and analytical ultracentrifugation. Spectral analysis, using absorption, fluorescence emission and far-UV circular dichroism spectroscopy were applied to compare the three recombinant protein complexes with the natural thermosome from P. occultum. All three recombinant complex species exhibit ATPase activity. Furthermore, we could demonstrate that the recombinant complexes slow down the aggregation of citrate synthase, alcohol dehydrogenase, and insulin. Thus, we conclude that the recombinant protein complexes exhibit a chaperone-like activity, interacting with non-native proteins; they do so at temperatures far below the lower physiological limit of growth.

Adenosine Triphosphatases↗
PubMed1998

Atomic force microscopy detects changes in the interaction forces between GroEL and substrate proteins.

The structure of the Escherichia coli chaperonin GroEL has been investigated by tapping-mode atomic force microscopy (AFM) under liquid. High-resolution images can be obtained, which show the up-right position of GroEL adsorbed on mica with the substrate-binding site on top. Because of this orientation, the interaction between GroEL and two substrate proteins, citrate synthase from Saccharomyces cerevisiae with a destabilizing Gly-->Ala mutation and RTEM beta-lactamase from Escherichia coli with two Cys-->Ala mutations, could be studied by force spectroscopy under different conditions. The results show that the interaction force decreases in the presence of ATP (but not of ATPgammaS) and that the force is smaller for native-like proteins than for the fully denatured ones. It also demonstrates that the interaction energy with GroEL increases with increasing molecular weight. By measuring the interaction force changes between the chaperonin and the two different substrate proteins, we could specifically detect GroEL conformational changes upon nucleotide binding.

Adenosine Triphosphate↗
PubMed1997

Specific detection of his-tagged proteins with recombinant anti-His tag scFv-phosphatase or scFv-phage fusions.

Using a cell-bound immunogen, we have generated a monoclonal antibody, 3D5, that recognizes carboxy-terminal oligo-histidine tags (His tags) on a wide variety of proteins. From this monoclonal antibody, we have generated a single-chain fragment of the variable domains (scFv), a dimeric scFv-alkaline phosphatase fusion and an oligovalent scFv-display phage. The antibody in its various formats is an effective tool used in fluorescence-activated cell sorting analysis, the BIAcore method, Western blots and enzyme-linked immunosorbent assay (ELISA). Western blots and ELISAs can be developed directly by using crude extracts of E.coli cells that produce the scFv-alkaline phosphatase fusion, thus providing an inexhaustable and convenient supply of detection reagent. Alternatively, oligovalent scFv-displaying phage can be used directly from culture supernatants for this purpose. The dissociation constants, KD of the peptide KGGHHHHH (KD = 4 x 10(-7) M) and of imidazole (KD = 4 x 10(-4) M) were determined. Molecular modeling of the Fv fragment suggests the occurrence of two salt bridges between the protonated histidine side chains of the peptide and the acidic groups in the antibody, explaining why the antibody or the substrate may be eluted under mildly basic conditions.

Antibodies, Monoclonal↗
PubMed1996

Effect of single point mutations in citrate synthase on binding to GroEL.

Six single point mutants of yeast citrate synthase were analyzed for binding to the molecular chaperone GroEL. In contrast to the wild-type and G276S, all other G276-mutants were able to displace pre-beta-lactamase from GroEL. The off-rate constant for pre-beta-lactamase must be at least partially rate-limiting, leading to an equilibrium dissociation constant between 10(-10) M and 10(-12)M. Direct evidence for binding of citrate synthase was obtained from gel filtration experiments. The results suggest that thermodynamic rather than structural features of the mutants determine the degree of binding to the chaperone.

Binding, Competitive↗
PubMed1994

Histamine in immunotherapy of advanced melanoma: a pilot study.

Sixteen patients with advanced metastatic malignant melanoma were treated with a high-dose infusion of interleukin-2 (IL-2; 18 x 10(6) IU/m-2 day-1) together with daily subcutaneous (s.c.) injections of interferon alpha (IFN alpha; 3 x 10(6) U/m-2 day-1) in 5-day cycles. Nine of these patients were given histamine (1 mg s.c.) twice daily during treatment with IL-2 and IFN alpha. In the seven patients who did not receive histamine, one partial response (that is a reduction of more than 50% in the total tumour burden) was observed in a patient with skin and lymph node melanoma. In the eight histamine-treated patients evaluable for response, four partial responses were observed. Two other patients showed regression at one site of metastasis but tumours remained unchanged at other sites. Two histamine-treated patients showed complete resolution of extensive liver metastasis. Sites of response in histamine-treated patients also included the subcutis, lymph nodes, skeleton, spleen and muscle. Lung melanoma did not respond to histamine/IL-2/IFN alpha. Three patients with lung tumours responded with significant (more than 50%) reduction of the volume of soft-tissue tumours, suggesting that the response to histamine may be organotropic. Survival was significantly prolonged in patients receiving histamine. Our data suggest that treatment with histamine may improve the antitumour efficacy of immunotherapy in metastatic melanoma.

Adult↗
PubMed1991

Collagen content in the rat urinary bladder following removal of an experimental infravesical outlet obstruction.

A partial urethral obstruction was induced in female rats. After 6 weeks, detrusor weight had increased eightfold and collagen concentration had decreased to about 40% compared to controls. Due to the weight gain, the total amount of detrusor collagen had increased more than threefold. Removal of the obstruction led to a rapid decrease in detrusor weight to 70, 34 and 30%, 2, 4 and 6 weeks postobstruction, although control levels were not reached. Collagen content decreased more slowly than detrusor weight, and for the same groups was 97, 69 and 67% of the value in the obstructed detrusor. This led to a rapid increase in detrusor collagen concentration which already 4 weeks after removal of the obstruction had increased to a level that did not significantly differ from the control value. The discrepancy between decrease in detrusor weight and in collagen content after removal of the obstruction suggests that a large proportion of the collagen synthesized during the period of outlet obstruction remained. Changes in the ratio between muscle and nonmuscle tissue were limited between control, obstructed and nonobstructed bladders. This suggests that the collagen concentration following obstruction and removal of obstruction is to a large extent due to changes in collagen concentration in the interstitial connective tissue rich in collagen.

Animals↗
PubMed1991

An interactive report generator for bone scan studies.

An interactive report generator for bone scintigraphy will be demonstrated. It comprises a controlled reporting vocabulary, an adaptive user interface, and a text generator. The controlled vocabulary represents the relevant concepts for bone scan reports: anatomical sites, scintigraphical phenomena, and diagnoses, and various attributes for these concept domains. Within the vocabulary selectional constraints are defined that restricts to meaningful combination of concepts. The interface provides intelligent views on the vocabulary, and presents only those terms that are relevant in a certain context. Through the interface the user may choose appropriate terms and combine them to complex findings. A German text generator for a restricted finding language transforms the entered data into morpho-syntactic surface structures and produces acceptable reports.

Bone and Bones↗
PubMed1990

Complexes of RecA protein in solution. A study by small angle neutron scattering.

RecA complexes on DNA and self-polymers were analysed by small-angle neutron scattering in solution. By Guinier analysis at small angles and by model analysis of a subsidiary peak at wider angles, we find that the filaments fall into two groups: the DNA complex in the presence of ATP gamma S, an open helix with pitch 95 A, a cross-sectional radius of gyration of 33 A and a mass per length of about six RecA units per turn, which corresponds to the state of active enzyme; and the compact form (bound to single-stranded DNA in the absence of ATP, or binding ATP gamma S in the absence of DNA, or just the protein on its own), a helical structure with pitch 70 A, cross-sectional radius of gyration 40 A and mass per length about five RecA units per turn, which corresponds to the conditions of inactive enzyme. The results are discussed in the perspective of unifying previous conflicting structural results obtained by electron microscopy.

Adenosine Triphosphate↗
PubMed1990

[Quantitative determination of cerebral perfusion using digital subtraction angiography (DSA)].

In a search for a reliable and relatively non-invasive method for quantifying cerebral perfusion, we examined the possible role of DSA. By using special software, it is possible to demonstrate vascular morphology and obtain functional data concerning blood flow. Regions of interest are used for obtaining time-density curves and these are evaluated by a formula designed by Meier and Zierler. Perfusion through the arterial territory in both cerebral hemispheres was correlated with the clinical symptoms of the patients and with the morphological findings. Difficulties and problems are described and discussed.

Angiography, Digital Subtraction↗