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Biomedical subjects

N Zimmermann

Publications and source records attributed to N Zimmermann.

At least 55 records · Page 3Linked to original sources
PubMed1996

Positive inotropic effects of the calcium sensitizer CGP 48506 in guinea pig myocardium.

In isolated papillary muscles from reserpinized guinea pigs, CGP 48506 increased force of contraction in a concentration-dependent and reversible manner, starting at 10 mumol/l and reaching 364.14 +/- 46.10% of predrug values at 100 mumol/l. The positive inotropic effect of CGP 48506 was not sensitive to 10 mumol/l carbachol. The positive inotropic effect of CGP 48506 was accompanied by increases in time to peak tension and in time of relaxation amounting to 223.37 +/- 6.87% and 247.10 +/- 9.34% of control, respectively, at 100 mumol/l (n = 10). CGP 48506 sensitized trabeculae from guinea pig hearts to calcium with an EC50 value of 22 mumol/l. However, CGP 48506 (up to 300 mumol/l) did not affect the activity of cardiac PDE isoenzymes I to IV. Likewise, CGP 48506 (up to 100 mumol/l) did not increase phosphorylation of select cardiac regulatory proteins or cyclic AMP content in guinea pig ventricular cardiomyocytes and did not affect cardiac phosphorylase phosphatase activity. CGP 48506 is the first pharmacological agent with noteworthy calcium-sensitizing properties that has been found to be devoid of inhibitory activity on cardiac PDE.

1-Methyl-3-isobutylxanthine↗
PubMed1996

Positive inotropic effects of the calcium sensitizer CGP 48506 in failing human myocardium.

In trabeculae carneae from failing human myocardium, CGP 48506 increased the force of contraction, which reached 310 +/- 41% of predrug values at 100 mumol/l. Its stereoisomer CGP 48508 did not affect the force of contraction (100 mumol/l). The positive inotropic effect of CGP 48506 was not sensitive to 10 mumol/l carbachol. The positive inotropic effect of CGP 48506 was accompanied by increases in time to peak tension and time of relaxation amounting to 175 +/- 4% and 205 +/- 15% of control, respectively, at 100 mumol/l. CGP 48506 but not CGP 48508 sensitized skinned trabeculae from failing human myocardium to calcium with an EC50 value of 10 mumol/l. However, CGP 48506 and CGP 48508 (up to 300 mumol/l) did not affect the activity of PDE isoenzymes I to IV from failing human myocardium. CGP 48506 is the first inotropic agent with calcium-sensitizing properties in the human heart that has been found to be devoid of inhibitory activity on human cardiac PDE isoenzymes.

1-Methyl-3-isobutylxanthine↗
PubMed1995

CTLs from lymphoid organs recognize an optimal HLA-A2-restricted and HLA-B52-restricted nonapeptide and several epitopes in the C-terminal region of HIV-1 Nef.

In a previous analysis of HIV-1-specific CTLs in lymphoid organs from HIV-seropositive patients, we reported high frequencies of in vivo differentiated CTLs directed against two immunodominant regions in the central and in the C-terminal part of the HIV-1 Nef protein. The present study analyzes the epitopes recognized by CTLs in the carboxyl terminus of Nef (amino acids 182-205). In addition to several epitopes that are recognized in association with different HLA molecules (A1, A2, A25(10), B35, B52), we defined an optimal nonapeptide (190-198). This nonapeptide was recognized by CTLs down to nanomolar concentrations in the context of at least two HLA molecules, HLA-B52 and HLA-A2, including three HLA-A2 subtypes: HLA-A2.1, -A2.2, and -A2.4. We also determined the relative frequencies of effector CTLs directed against peptide 190-198 to be as high as 10(-4), as opposed to lower frequencies ranging between 5 x 10(-5) and 5 x 10(-6) observed for the other peptides recognized in the same region, thus confirming the optimal presentation of this nonapeptide in vivo. Molecular modeling of the interactions between HLA-A2.1 and Nef peptide 190-198 suggests the formation of a stable complex and allowed us to study sequence motifs that are important for the binding of the HIV-1 peptide in the pockets of the HLA-A2.1 molecule.

Base Sequence↗
PubMed1995

The tetracyclic lantibiotic actagardine. 1H-NMR and 13C-NMR assignments and revised primary structure.

The primary structure of the peptide lantibiotic actagardine was determined in (2H3)acetonitrile/H2O by homonuclear two- and three-dimensional NMR spectroscopy as well as 2D 1H(13C) correlation spectra at natural abundance. Actagardine was found to be a tetracyclic 19-residue peptide containing one lanthionine and three overlapping beta-methyllanthionine bridges. Sequential resonance assignment and location of the four thioether rings was accomplished by 2D NOESY, 3D NOESY-TOCSY and gradient-enhanced 1H(13C)-HMBC spectra. The C-terminal thioether bridge was shown to be oxidized to a sulfoxide. The NMR data were additionally confirmed by mass spectrometry and Edman degradation after chemical modification, which allowed sequencing of lanthionine and beta-methyllanthionine residues. Our studies clearly show, that the structure of actagardine as previously published by Kettenring et al. (1990) J. Antibiot. 43, 1082-1088 is not correct.

Alanine↗
PubMed1995

Mechanisms of the contractile effects of flosequinoxan.

In guinea-pig papillary muscles the positive inotropic effect of flosequinoxan (BTS) starting at 100 mumol/l amounted to 287.6 +/- 34.2% at 300 mumol/l without any effects on time to peak tension (103.9 +/- 2%) and relaxation time (107.1 +/- 6.7% of predrug value, respectively). 10 mumol/l carbachol attenuated the positive inotropic effect of 300 mumol/l to 166.5 +/- 11.6% (n = 10). The phosphorylation state of the inhibitory subunit of troponin (TnI) and phospholamban (PLB) in [32P]-labeled guinea-pig ventricular myocytes was increased starting at 100 mumol/l amounting to 142.5 +/- 12.6% and 130.9 +/- 2.2% at 300 mumol/l, respectively (n = 5). Furthermore, BTS (300 mumol/l) decreased phosphorylase phosphatase activity by 23.1%. It is concluded that the contractile effects of BTS are accompanied by enhanced phosphorylation of regulatory proteins which could in part be due to inhibition of phosphorylase phosphatase activity.

Adenosine Triphosphatases↗
PubMed1995

Comparison of the stereoselective effects of a thiadiazinone derivative on contractile parameters and protein phosphorylation in the mammalian ventricle.

In papillary muscles from reserpinized guinea pigs, EMD 57033, the most potent Ca(2+)-sensitizer known, effectively increased force of contraction (FOC) and concomitantly increased duration of contraction. In isolated 32P-labeled guinea pig ventricular cardiomyocytes, EMD 57033 increased the phosphorylation state of phospholamban as well as the inhibitory subunit of troponin, which are usually linked to reductions in contraction time. Therefore, EMD 57033 dissociates phospholamban-phosphorylation and effects on contractile parameters, probably owing to its strong Ca(2+)-sensitizing properties.

Adenosine Triphosphatases↗
PubMed1995

On the cardiac contractile, biochemical and electrophysiological effects of cantharidin, a phosphatase inhibitor.

Cantharidin concentration dependently increased the force of contraction in isolated guinea pig papillary muscles (1-100 microM). The positive inotropic effect is accompanied by a reduction in time to peak tension and relaxation time. Cantharidin did not exert a positive chronotropic effect in spontaneously beating right atria. L-type calcium channel currents of guinea pig cardiomyocytes were moderately increased by cantharidin (by about 20%), both at the whole-cell level (2 mM Ca2+) and at the single channel level (70 mM Ba2+). There was a correspondingly small increment of single channel availability. Additionally, a larger proportion of single-channel sweeps displayed high open probability-gating (so-called mode 2-gating). Cantharidin inhibited both type 1 and type 2A phosphatase activity in phosphatases purified from guinea pig ventricles [IC50 2.70 (2.06-3.53) and 0.13 (0.05-0.34) microM, n = 5-6, with 95% confidence intervals, respectively]. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, cantharidin (10 microM) increased the phosphorylation state of phospholamban (to 210% of control), the inhibitory subunit of troponin (to 155% of control), C-protein (to 156% control) and various additional proteins. It is concluded that the effects of cantharidin are likely mediated by increasing the phosphorylation state of several regulatory proteins. Furthermore, cantharidin might be an economical tool to investigate the function of phosphatases in model organ systems.

Animals↗
PubMed1994

Biochemical and electrophysiological mechanisms of the positive inotropic effect of calyculin A, a protein phosphatase inhibitor.

Calyculin A (CyA; 1 microM) increased the force of contraction in isolated guinea pig papillary muscles to 144% of control without affecting contraction parameters. The effect of CyA on L-type calcium channels was assessed in cell-attached patches of guinea pig ventricular cardiomyocytes. Unitary Ba++ current recordings revealed that CyA at micromolar concentrations enhanced channel availability almost 2-fold, whereas the duration of individual openings and closures remained unchanged. In whole-cell recordings with Ca++ as the charge carrier, intracellular dialysis of 1 microM CyA enhanced peak current to a similar extent. In homogenates from guinea pig ventricles, 1 microM CyA completely inhibited phosphorylase phosphatase activity. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, 1 microM CyA increased the phosphorylation state of phospholamban (to 267% of control), that of the inhibitory subunit of troponin (to 182% of control) and those of various additional proteins. We conclude that the effects of CyA are likely to be mediated by increasing the phosphorylation state of several regulatory proteins.

Animals↗
PubMed1993

Solution structures of the lantibiotics duramycin B and C.

The solution structures of the lantibiotics duramycin B in H2O/2H2O (9:1) and duramycin C in (2H3)acetonitrile/H2O (1:1) have been determined by NMR followed by distance-geometry and restrained-molecular-mechanics calculations. The constitution and location of three thioether bridges and a lysinoalanine ring system could be established by unambiguously assigned NOE contacts between the bridging side chains. Model building based on NMR constraints resulted in a U-shaped topology of the tetracyclic 19-peptides with a turn around Pro9 and a kink along a virtual line from residues 5 to 13. This clamp-like conformation is stabilized by the thioether bridges and is additionally supported by an antiparallel beta-strand-like structure of the N-termini and C-termini and the inherent amphiphilicity of duramycin-type lantibiotics. The duramycins B and C differ mainly in the relative mobilities of their rings A, C and D. Duramycin B is closely related to cinnamycin with an exchange of Phe10 to leucine, whereas duramycin C differs from duramycin B by three conserved and two non-conserved amino-acid exchanges.

Amino Acid Sequence↗
PubMed1992

Molecular dynamics study of a complex between the human histocompatibility antigen HLA-A2 and the IMP58-66 nonapeptide from influenza virus matrix protein.

The structure of the influenza-virus-matrix-protein (IMP) 58-66 nonapeptide, bound to the major-histocompatibility-complex-encoded human leukocyte antigen (HLA) A2 protein was studied by molecular dynamics simulation. Starting from the extra electron density map of peptides co-crystallized with HLA-A2, the nonapeptide IMP58-66 was docked residue by residue in the protein binding cleft. The complex was simulated for 100 ps in a shell of 1372 water molecules. The averaged simulated HLA-A2 conformation was found to be similar to the crystal structure (0.182 nm RMS deviation, for the backbone atoms of the alpha 1-alpha 2 domain). Nine out of the 14 hydrogen bonds observed in the antigen-binding site were reproduced in the simulation. The IMP58-66 peptide exhibits an extended conformation with kinks at positions 3 and 5. The side chains of residues 2, 3 and 9 develop van der Waals' interactions with hydrophobic pockets of HLA-A2, corresponding to polymorphic residues of the major-histocompatibility-complex-encoded proteins. Both the N-terminus and C-terminus of the nonapeptide were anchored in the antigen-binding groove by hydrogen bonds with conserved amino acids. The N-terminus was more flexible and contacts four HLA-A2 conserved tyrosines (Tyr7, Tyr59, Tyr159 and Tyr171) and Glu63 by direct or water-relayed hydrogen bonds. Water intercalation occurred only around the N-terminus of the peptide, the C-terminal carboxylate forming strong hydrogen bonds with polar residues (Tyr84 and Thr143) and a salt bridge with Lys146 all over the molecular dynamics simulation. This model is fully compatible with the recently published crystal structure of the HLA-B27 protein, complexed by a mixture of self nonapeptides.

Amino Acid Sequence↗
PubMed1991

Conformational and epitope mapping of herpes-simplex-virus type-1 thymidine kinase using synthetic peptide segments.

Adjacent peptide segments covering the complete sequence of herpes-simplex-virus type-1 thymidine kinase (HSV1-TK) of 376 amino acids were synthesized in order to experimentally verify the three-dimensional structure of the HSV1-TK active site, which was previously determined by molecular modeling. 26 peptides have been prepared by multiple solid-phase synthesis using the 9-fluorenylmethoxycarbonyl strategy. The purified peptides were linked covalently to bovine serum albumin. The peptide/ELISA of the synthesized bovine-serum-albumin conjugates using polyclonal rabbit anti(HSV1-TK)serum resulted in ten epitopes, which correlate excellently with the computer-proposed active site of HSV1-TK. CD spectra of the HSV1-TK peptides were recorded in trifluoroethanol/water (9:1 by vol.) An eigenvalue method based on CD spectra of 15 well known protein structures was used to calculate the relative percentage of secondary structures from the CD data. The computer model of the HSV1-TK showed full conformity with the folding pattern determined by CD of the synthetic peptide segments. Therefore, conformational peptide mapping with CD-based secondary structures combined with epitope mapping from the peptide/ELISA is an efficient and reliable method to support computer-aided protein design.

Amino Acid Sequence↗
PubMed1991

Improved light microscopic demonstration of D-amino acid oxidase activity in cryotome sections using cerium ions as capturing and amplifying agent--the Ce/Ce-H2O2-DAB procedure.

The light microscopical demonstration of D-amino acid oxidase (AAOX) activity with cerium (Ce III) as the capturing agent was improved. The incubation medium was stabilized by the employment of triethanolamine and detrane complexed cerium. A considerable increase in intensity of the reaction was accomplished by treatment of the AAOX-incubated sections with Ce III which reacted with the primary reaction product Ce IV-perhydroxide to form Ce IV-hydroxide. In this way the primary reaction product was reduced and enlarged concomitantly. The Ce IV-hydroxide was converted into Ce IV-perhydroxide by H2O2, which was visualized by blue-black stained Ni-DAB complexes. Thus, Ce III is used as capturing agent as well as amplifier (Ce/Ce-H2O2-DAB method). The primary reaction product Ce III-phosphate formed by coreacting phosphatases was selectively extracted by citrate containing glycine-NaOH buffer while Ce IV-perhydroxide remained in the sections. In model experiments it was proven that the perhydroxide groups in the Ce IV-perhydroxide compound initiate predominantly the DAB polymerization while the contribution of Ce III and Ce IV is small.

3,3'-Diaminobenzidine↗
PubMed1990

[Does induced Heinz body formation lead to the liberation of IgG receptors on the erythrocyte membrane?].

Immunofluorescence microscopical and biochemical studies led other authors to the conclusion that the formation of membrane-bound Heinz bodies at these parts of the plasmalemma of erythrocytes leads to clustering of band 3-protein and increased binding of IgG. We failed to detect immunocytochemically an increased IgG binding over phenylhydrazine induced membrane-bound Heinz bodies in otherwise intact erythrocytes using transmission electronmicroscopy and we also did not notice any clustering of intramembraneous particles over the numerous Heinz bodies by means of freeze etching. Especially at higher phenylhydrazine concentrations the erythrocytes show formation of vesicles and hemolysis accompanied by increased IgG binding and clustering of the intramembraneous particles. Photographs of such cells obtained by immunofluorescence microscopy are very similar to the pictures known from the literature.

Anion Exchange Protein 1, Erythrocyte↗