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Biomedical subjects

O Jahn

Publications and source records attributed to O Jahn.

At least 19 recordsLinked to original sources
PubMed2006

Measurement of the Gerasimov-Drell-Hearn Integrand for 2H from 200 to 800 MeV.

A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200<Egamma<800 MeV. The experiment used a 4pi detection system, a circularly polarized tagged photon beam and a frozen-spin target which provided longitudinally polarized deuterons. The contribution to the Gerasimov-Drell-Hearn sum rule for the deuteron determined from the data is 407+/-20(stat)+/-24(syst) mu b for 200<Egamma<800 MeV.

Journal Article↗
PubMed2002

Helicity amplitudes A1/2 and A3/2 for the D13(1520) resonance obtained from the gamma-->p-->-->ppi(0) Reaction.

The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.

Journal Article↗
PubMed2002

Neutron polarizabilities investigated by quasifree Compton scattering from the deuteron.

Measuring Compton scattered photons and recoil neutrons in coincidence, quasifree Compton scattering by the neutron has been investigated at MAMI (Mainz) at theta(lab)(gamma) = 136 degrees in an energy range from 200 to 400 MeV. From the data a polarizability difference of alpha(n)-beta(n) = 9.8+/-3.6(stat)+2.1-1.1(syst)+/-2.2(model) in units of 10(-4) fm(3) has been determined. In combination with the polarizability sum alpha(n)+beta(n) = 15.2+/-0.5 deduced from photoabsorption data, the first precise results for the neutron electric and magnetic polarizabilities, alpha(n) = 12.5+/-1.8(stat)+1.1-0.6(syst)+/-1.1(model) and beta(n) = 2.7-/+1.8(stat)+0.6-1.1(syst)-/+1.1(model), are obtained.

Journal Article↗
PubMed2002

Pharmacology and biology of corticotropin-releasing factor (CRF) receptors.

The biology of corticotropin-releasing factor (CRF) finds increasing interest in the scientific community because of the neuromodulatory actions of CRF on brain functions such as learning, anxiety, feeding, and locomotion. Additional actions on immunumodulation and apoptosis have recently been discovered. All actions of CRF are mediated by G protein-coupled receptors, which trigger different, sometimes opposite actions in different regions of the central nervous system. The CRF system exhibits considerable plasticity by the involvement of numerous different ligands, splice variants, and transductional couplings. The generation of multiple splice variants is facilitated by the intron exon structure of the CRF receptor genes.

Amino Acid Sequence↗
PubMed2001

Electromagnetic compatibility of electronic implants--review of the literature.

The aim of the article was to provide an overview of published studies regarding the electromagnetic compatibility (EMC) of electronic implants. The available literature was sorted according to combinations of implant types and sources of interference. Several experiments concerning the susceptibility of pacemakers to mobile phones have been performed. The results of these experiments suggest measures that may be used to prevent the disturbance of pacemakers. For instance, instead of carrying the activated mobile phone in the breast pocket it is recommended that a distance of 30 cm be maintained between the pacemaker and the mobile phone, and that the mobile phone be used on the contralateral side of the pacemaker's location. Similar measures may be recommended for patients with implantable cardioverter defibrillators when using mobile phones. Patients with electronic implants should walk rapidly through anti theft-devices because some of these devices are liable to disturb implants. Patients with cardiac pacemakers should not be subjected to magnetic resonance imaging as far as possible. For a variety of combinations of implants and interference sources, e.g. cardiac pacemakers and base station antennas, no studies were found in the literature. It is strongly recommended that trials be carried out to evaluate the potential risk for patients in these settings.

Cochlear Implants↗
PubMed2001

A single amino acid serves as an affinity switch between the receptor and the binding protein of corticotropin-releasing factor: implications for the design of agonists and antagonists.

In view of the observation that corticotropin-releasing factor (CRF) affects several brain functions through at least two subtypes of G protein-dependent receptors and a binding protein (CRFBP), we have developed synthetic strategies to provide enhanced binding specificity. Human/rat CRF (h/rCRF) and the CRF-like peptide sauvagine (Svg), differing in their affinities to CRFBP by two orders of magnitude, were used to identify the residues determining binding to CRFBP. By amino acid exchanges, it was found that Ala(22) of h/rCRF was responsible for this peptide's high affinity to CRFBP, whereas Glu(21) located in the equivalent position of Svg prevented high affinity binding to CRFBP. Accordingly, [Glu(22)]h/rCRF was not bound with high affinity to CRFBP in contrast to [Ala(21)]Svg, which exhibited such high affinity. Furthermore, the affinity of both peptides to either CRF receptor (CRFR) subtype was not reduced by these replacements, and their subtype preference was not changed. Thus, exchange of Ala and Glu and vice versa in positions 22 and 21 of h/rCRF and Svg, respectively, serves as a switch discriminating between CRFBP and CRFR. On the basis of this switch function, development of new specific CRF agonists and antagonists is expected to be facilitated. One application was the modification of the CRF antagonist astressin (Ast), whose employment in animal experiments is limited by its low solubility in cerebrospinal fluid. Introduction of Glu residues into Ast generated with [Glu(11,16)]Ast an acidic astressin, which efficiently antagonized in vivo the CRFR1-dependent reduction of locomotion induced by ovine CRF without detectable binding to CRFBP.

Amino Acid Sequence↗
PubMed2001

Pharmacological characterization of recombinant rat corticotropin releasing factor binding protein using different sauvagine analogs.

Little is known on the structural ligand requirements for corticotropin-releasing factor binding protein (CRFBP) of the rat used as an important experimental animal. To obtain such information recombinant rat CRFBP was produced in stably transfected HEK 293 cells. The primary structure and posttranslational processing of purified rat CRFBP was established by peptide mapping using HPLC combined with mass spectrometric analysis. Rat CRFBP was pharmacologically characterized employing a competition binding assay with tritium-labeled rat urocortin. The rank order of declining affinity of various CRF analogs was urotensin-I, human/rat CRF (h/rCRF), rat urocortin, sauvagine (Svg), and ovine CRF in agreement with the rank order found for human CRFBP. In contrast to astressin, the CRF receptor 2-selective antagonist anti-sauvagine-30 did not show any detectable specific binding to rat CRFBP. The significance of residues 10 to 12 and 21 to 24 of Svg for its low affinity binding was established by changing these residues of Svg to those of h/rCRF. The corresponding residues 22 to 25 of h/rCRF represented the ARAE motif determined to be crucial for binding in agreement with reported data on human CRFBP. Residues 11 to 13 of CRF introduced into Svg also enhanced the affinity to rat CRFBP.

Amino Acid Sequence↗
PubMed2001

Functional and protein chemical characterization of the N-terminal domain of the rat corticotropin-releasing factor receptor 1.

Rat corticotropin-releasing factor receptor 1 (rCRFR1) was produced either in transfected HEK 293 cells as a complex glycosylated protein or in the presence of the mannosidase I inhibitor kifunensine as a high mannose glycosylated protein. The altered glycosylation did not influence the biological function of rCRFR1 as demonstrated by competitive binding of rat urocortin (rUcn) or human/rat corticotropin-releasing factor (h/rCRF) and agonist-induced cAMP accumulation. The low production rate of the N-terminal domain of rCRFR1 (rCRFR1-NT) by transfected HEK 293 cells, was increased by a factor of 100 in the presence of kifunensine. The product, rCRFR1-NT-Kif, bound rUcn specifically (K(D) = 27 nM) and astressin (K(I) = 60 nM). This affinity was 10-fold lower than the affinity of full length rCRFR1. However, it was sufficiently high for rCRFR1-NT-Kif to serve as a model for the N-terminal domain of rCRFR1. With protein fragmentation, Edman degradation, and mass spectrometric analysis, evidence was found for the signal peptide cleavage site C-terminally to Thr(23) and three disulfide bridges between precursor residues 30 and 54, 44 and 87, and 68 and 102. Of all putative N-glycosylation sites in positions 32, 38, 45, 78, 90, and 98, all Asn residues except for Asn(32) were glycosylated to a significant extent. No O-glycosylation was observed.

Amino Acid Sequence↗
PubMed2000

Electromagnetic fields: low dose exposure, current update.

OBJECTIVES: The controversial discussion of low-dose electromagnetic field (EMF) effects on human health derives from a lack of knowledge of the mechanism of action and proven results of cellular, animal and human experiments. The paper gives an overview of the current results of scientific research. METHODS: Review based on the legal measurements of the EU parliament, the ICNIRP guidelines, the current literature and personal contacts with scientist in the field. RESULTS: Epidemiologic research shows a low degree of association, inconsistency and missing dose-effect relations. A biologic mechanism of action is still debatable. When observing ICNIRP guideline values, no harm to human health has been shown; but the statement, "EMF are not harmful", cannot be made. Implanted electric devices, like pace-makers, are more sensitive to EMF and need special attention. CONCLUSION: There is no scientific basis as to the harmful effects of EMFs on human health, when ICNIRP guidelines are observed. Hypersensitivity to EMF has not been clinically proved.

Animals↗
PubMed2000

[Electromagnetic fields--effects on health].

This literature review shows the current knowledge of health effects on humans concerning static, low frequency electric and magnetic fields and high frequency electromagnetic fields up to 300 GHz. Basic physical knowledge and the current thresholds are demonstrated. Different frequency ranges of electromagnetic fields, their natural and technical origins and the different biological effects, especially possible hazards such as cancerogenity or risks for the brain, are discussed. Open questions and future research aspects are demonstrated. Finally electrosensibility and psychological aspects are shown.

Animals↗
PubMed1999

Actions of CRF and its analogs.

Corticotropin-releasing factor (CRF), urocortin, sauvagine and urotensin I form the CRF family. These peptides bind with different affinities to two subtypes of CRF receptor (CRFR), CRFR1 and CRFR2. The latter exists as two splice variants, the neuronal CRFR2a and the peripheral CRFR2b. CRFR is a G protein-dependent receptor which acts mainly through Gs enhancing cAMP production. However, CRFR1 expressed in neutrophils of the spleen in response to immunologic stimulation and psychological stress does not seem to function through Gs, as indicated by the inability of CRF to stimulate the cAMP production of CRFR1+ neutrophils. Besides the two receptors, a 37 kD CRF binding protein (CRF-BP) binds several CRF peptides with high affinity. CRFR and CRF-BP do not share a common amino acid sequence representing the ligand binding site. In view of the unusually slow offrate of CRF-BP, it is proposed that CRF-BP provides an efficient uptake of free extracellular CRF. Thus, the time of exposure of CRFR to CRF or urocortin can be limited. At this time, the fate of the ligand CRF-BP complex is unclear. CRFR1 is not only involved in the hypophyseal stimulation of corticotropin release, but hippocampal CRFR1 mediates enhancement of stress-induced learning. CRFR1 may also be involved in basic anxiety. In contrast, at least in the mouse, CRFR2 of the lateral intermediate septum mediates tonic impairment of learning. In response to stressful stimuli or after local injection of high CRF doses, CRFR2 mediates anxiety. Effects requiring CRFR2 can be blocked specifically by the recently developed peptidic antagonist antisauvagine-30.

Amino Acid Sequence↗
PubMed1996

[Passive smoking, a risk factor for lung carcinoma?].

The established elevated risk of lung cancer in smokers led to the hypothesis that environmental tobacco smoke (ETS) also causes malignancies. The solution of this question is complicated by low exposure levels and dose-response dependence, as well as threshold levels. The differences between the toxins in the main- and side-stream of tobacco smoke and also the lack of significantly elevated risk ratios in epidemiological studies do not permit scientific conclusions endorsing a connection between passive smoking and lung cancer, which has become an emotionalised issue.

Humans↗
PubMed1992

Sequence of the tufA gene encoding elongation factor EF-Tu from Thermus aquaticus and overproduction of the protein in Escherichia coli.

The sequence of the tufA gene from the extreme thermophilic eubacterium Thermus aquaticus EP 00276 was determined. The GC content in third positions of codons is 89.5%, with an unusual predominance of guanosine (60.7%). The derived protein sequence differs from tufA- and tufB-encoded sequences for elongation factor Tu (EF-Tu) of Thermus thermophilus HB8, another member of the genus Thermus, in 10 of the 405 amino acid residues. Three exchanges are located in the additional loop of ten amino acids (182-191). The loop, probably involved in nucleotide binding, is absent in EF-Tu of the mesophile Escherichia coli. Since EF-Tu from E. coli is quite unstable, the protein is well-suited for analyzing molecular changes that lead to thermostabilization. Comparison of the EF-Tu domain I from E. coli and Thermus strains revealed clustered amino acid exchanges in the C-terminal part of the first helix and in adjacent residues of the second loop inferred to interact with the ribosome. Most other exchanges in the guanine nucleotide binding domain are located in loops or nearest vicinity of loops suggesting their importance for thermostability. The T. aquaticus EF-Tu was overproduced in E. coli using the tac expression system. Identity of the recombinant T. aquaticus EF-Tu was verified by Western blot analysis, N-terminal sequencing and GDP binding assays.

Amino Acid Sequence↗
PubMed1991

Analysis of the spc ribosomal protein operon of Thermus aquaticus.

The gene region of Thermus aquaticus corresponding to the distal portion of the S10 operon and to the 5'-portion of the Escherichia coli spc operon was cloned, using the E. coli gene for the ribosomal protein L5 as hybridization probe. The gene arrangement was found to be identical to E. coli, i.e. S17, L14, L24, L5, S14, S8 and L6. Stop and start regions of contiguous cistrons overlap, except for the S14-S8 intergenic region, whose size (67 bases) even exceeds the corresponding spacer regions in E. coli and Bacillus subtilis. A G + C content of 94% in third positions of codons was found in the ribosomal protein genes of T. aquaticus analyzed here. The stop codon of gene S17 (the last gene of the S10 operon in E. coli) and the start codon of gene L14 (the first gene of the spc operon in E. coli) overlap in T. aquaticus, thus leaving no space to accommodate an intergenic promoter preceding spc-operon-encoded genes in T. aquaticus. A possible promoter, localized within the S17 coding region, yielded only weak resistance (20 micrograms/ml) to chloramphenicol in E. coli and therefore could be largely excluded as the main promoter for spc-operon-encoded genes. We failed to detect a structure resembling the protein S8 translational repressor site, located at the beginning of the L5 gene in E. coli, in the corresponding region or any other region in the cloned T. aquaticus spc DNA.

Base Sequence↗
PubMed1991

Comparative analysis of ribosomal protein L5 sequences from bacteria of the genus Thermus.

The genes for the ribosomal 5S rRNA binding protein L5 have been cloned from three extremely thermophilic eubacteria, Thermus flavus, Thermus thermophilus HB8 and Thermus aquaticus (Jahn et al, submitted). Genes for protein L5 from the three Thermus strains display 95% G/C in third positions of codons. Amino acid sequences deduced from the DNA sequence were shown to be identical for T flavus and T thermophilus, although the corresponding DNA sequences differed by two T to C transitions in the T thermophilus gene. Protein L5 sequences from T flavus and T thermophilus are 95% homologous to L5 from T aquaticus and 56.5% homologous to the corresponding E coli sequence. The lowest degrees of homology were found between the T flavus/T thermophilus L5 proteins and those of yeast L16 (27.5%), Halobacterium marismortui (34.0%) and Methanococcus vannielii (36.6%). From sequence comparison it becomes clear that thermostability of Thermus L5 proteins is achieved by an increase in hydrophobic interactions and/or by restriction of steric flexibility due to the introduction of amino acids with branched aliphatic side chains such as leucine. Alignment of the nine protein sequences equivalent to Thermus L5 proteins led to identification of a conserved internal segment, rich in acidic amino acids, which shows homology to subsequences of E coli L18 and L25. The occurrence of conserved sequence elements in 5S rRNA binding proteins and ribosomal proteins in general is discussed in terms of evolution and function.

Amino Acid Sequence↗
PubMed1989

Detection of an insensitive ornithine-carbamoyltransferase in strains of Pseudomonas syringae pv. phaseolicola with different phytotoxin-generating capacities.

Independently of their capacity to produce phytotoxins, strains of Pseudomonas syringae pv. phaseolicola contain two ornithine carbamoyltransferases (OCT, EC 2.1.3.3) which differ in resistance to phaseolotoxin and Orn-P(O) (NH2)-NH-SO3 H (PNSOrn). At 18 degrees C, the optimal temperature for product formation, the balance of the two types of OCT was shifted in favour of the insensitive type in phaseolotoxin producing strains, and in favour of the sensitive one in strains with little or no toxin production. The results suggest a causal relationship between the existence of an insensitive enzyme and the synthesis of toxins.

Drug Resistance↗
PubMed1989

Inhibition of ornithine carbamoyltransferase from Pseudomonas syringae pv. syringae W50 by phaseolotoxin.

In contrast to the producer of phaseolotoxin and Orn-P(O)(NH2)-NH-SO3H (PNSOrn), Pseudomonas syringae pv. phaseolicola, which possesses a sensitive and an insensitive type of ornithine carbamoyltransferase (OCT, E.C. 2.1.3.3.), in Pseudomonas syringae pv. syringae W50, an organism which produce neither phaseolotoxin nor PNSOrn, only one type of OCT could be detected. This enzyme is highly sensitive to phaseolotoxin. This result supports our hypothesis that the existence of an insensitive ornithine carbamoyltransferase is an important prerequisite for the synthesis of phaseolotoxin in P. syringae pv. phaseolicola and that this enzyme does not occur generally in P. syringae spec.

Drug Resistance↗