Biomedical subjects

F Heitz

Publications and source records attributed to F Heitz.

At least 145 records · Page 8Linked to original sources

PubMedDate not supplied

Side-chain interactions and conformation in alpha-helical poly(gamma-phenacyl L-glutamate). Aggregation in dilute solutions.

The behavior of alpha-helical poly(gamma-phenacyl L-glutamate) (PPLG) has been studied by hydrodynamic, optical rotation, dielectric, and nmr measurements in different solvents. Special attention has been paid to side-chain interactions which depend on the ease of solvation of the phenacyl chromophore. Thus, in hexafluoro-2-propanol the circular dichroism spectrum is very similar to that usually observed for an alpha helix, and hydrogen bonding was shown to occur between the solvent and phenacyl CO group. In other heliocogenic solvents, side chain-side chain interactions occur. In dimethylformamide and pyridine they give rise at low temperature and low concentrations to an aggregation phenomenon whose molecular mechanism implies a molecular weight dependent folding of the molecules. Models for the side-chain conformation are proposed for the polymer in the solid state on the basis of infrared dichroism.

Binding Sites↗

PubMedDate not supplied

alpha and piDL helical states of alternating poly(gamma-benzyl D-L-glutamate) in solution.

As in solid state, strictly alternating poly(gamma-benzyl D-L-glutamate) in solution can adopt two different helical conformations. Besides the alpha helix, a second helical conformation is found at higher temperatures in dioxane and chloroform, the properties of which correspond to that of the piDL4 helix. As the molecules have a finite length a screw sense is favored for both helical forms thus giving rise to optical activity allowing the study of the transconformation by optical rotatory dispersion and circular dichroism besides infrared and dielectric measurements. Thus, as the temperature is raised the equilibria right-left handed alpha helices and alpha-piDL helical forms can be followed. The favored screw senses are determined by the number of interacting side chains for the alpha helix and by the number of hydrogen bonds which are formed in the piDL helical conformation. The side chain-side chain interactions in the alpha helix are experimentally shown to be attractive.

Glutamates↗

PubMedDate not supplied

High-resolution nuclear magnetic resonance studies at 270 MHZ of alternating and random poly(benzyl D,L-glutamates).

The solution conformations of several D,L copoly benzyl glutamates both random and alternating are studied by comparing their NMR spectra in chloroform and also in dioxane and dimethylformamide. The alpha CH chemical shifts characteristic of the alpha helix of strictly alternating DL copolymers in chloroform/0.5% TFA are established (3.65 and 3.82 ppm) and differ from that of the regular alpha helix (3.92 ppm). It is concluded that alternating copolymers prepared by an essentially racemization-free method are completely in the alpha-helical conformation which is characteristic of strictly alternating D-L copolymers, whereas random copolymers are largely regular alpha. The alpha leads to piDL helix/helix transition of an alternating copolymer in dioxane has been monitored and the alpha CH resonance characteristic of the piDL helix is found to be at the unusually low chemical shift of 4.45 ppm.

Glutamates↗

PubMedDate not supplied

Structural properties of double-stranded helical poly (gamma-benzyl-D-L-glutamate) in solution. Comparison with some solution properties of linear gramicidin.

The double-stranded helical conformations of alternating PBD-LG found in the solid state have been studied in infrared, circular dichroism, and NMR techniques in solution in methylene chloride, chloroform dioxane, and collidine. The infrared and CD properties of the solutions, transconformations between single- and double-stranded helices and transconformations within the family of double helices, support the hypothesis that the conformation in solution is the same as that found after evaporation of the solvent, namely the pi pi DL 7.2, pI pI DL 9.0, and pi pi DL 10.8 helices, depending on the solvent. An attempt to identify the conformation of linear gramicidin is made on the basis of the CD spectra and the infrared frequencies conformation relationship established for PBD-LG. However, owing to the great number of different conformations observed for the antibiotic, no firm conclusion can yet be drawn, except for the probable existence of the double antiparallel helical structure.

Benzyl Compounds↗

PubMedDate not supplied

High-resolution NMR studies at 270 MHz of alternating poly(gamma-benzyl D-L-glutamate) in double-stranded helical conformations.

NMR spectra (270MHz) are presented of strictly alternating poly(gamma-benzyl D-L-glutamate) in dioxane, chloroform, and methylene chloride solutions from which cast films have been demonstrated to have a molecular conformation in the pi pi DL 9.0 and pi pi DL 7.2 double-helical forms. Unusually low chemical shift values are observed for the alpha-CH (approximately 5.5 ppm) and NH (approximately 9.0 ppm) resonances, well separated from those of the alpha and pi DL single helices. The aromatic protons and benzyl-CH2 resonances are found slightly upfield of those of the single helices. It is proposed that these shift values are characteristic of the double helices and that the conformation of the PBD-LG sample in these solvents is the same as in the film obtained therefrom. This conclusion is supported by NMR spectra of a solvent-induced pi pi DL 7.2 leads to pi pi DL 9.0 double helical transconformation and a similar TFA-induced double helix leads to single helix conformational transition.

Benzyl Compounds↗

PubMedDate not supplied

Helical structures of poly(D-L-peptides). A conformational energy analysis.

Conformational energy calculations are reported for a number of possible helical structures of poly(D-L-peptides): the alpha helix, two single-stranded piDL, and five double-stranded pipiDL helices. For a poly(D-alanine-L-alanine) sequence, the energies of the various helices are found to differ by less than 1 kcal/(mol residue). For some helices (especially the piDL ones) two structural variants are predicted. These variants, called "goniomers", are characterized by reversed sequences of conformational angles but have the same screw sense and similar helical parameters. A biological implication of these goniomers is suggested, and their usefulness as a critical test for energy calculations is considered.

Alanine↗

PubMedDate not supplied

13C NMR spectroscopy of alternating poly(gamma-benzyl D-L-glutamate) in alpha- and double-helical conformations.

Carbon-13 NMR spectra of alpha single-helical and pipiDL double-helical conformations of alternating poly (gamma-benzyl D-L-glutamate) are presented. In both cases, the existence of doublet for the backbone carbon atoms is consistent with D and L residues being in different conformational states when engaged in the same helix. The resonances of the Calpha atoms in both helices, which are found at identical chemical shifts, and comparison with the 1H NMR observation, favor the hypotheses that solvent molecules are located inside the helical core of the double helices.

Glutamates↗

PubMedDate not supplied

Steroid-induced spinal epidural lipomatosis: CT survey.

A new case of spinal cord compression secondary to steroid-induced epidural lipomatosis is reported in a patient treated for dermatomyositis. Computed tomography was performed before the institution of steroid therapy, during spinal cord compression, and after effective surgical treatment. The development of epidural lipomatosis does not require a preexisting lipoma and may occur in a previously normal spine.

Epidural Space↗

PubMedDate not supplied

Correlations between biological activity and structural properties for two short homologous sequences in thymosin beta4 and gelsolin.

Gelsolin and thymosin beta4 appear to be two important actin-associated proteins involved in the regulation of actin polymerization. It has been widely demonstrated that thymosin is the major cellular actin-sequestering factor shifting the polymerization equilibrium of actin towards a monomeric state. At the same time gelsolin, a Ca2+ and inositol phosphate sensitive protein, regulates actin filament length. The interactions of these two proteins with actin are rather complex and require the participation of several complementary peptide sequences. We have identified a common motif, (I, V)EKFD, in the two proteins in the functional sequences so far examined. Gelsolin- and thymosin beta4-related peptides including the common motif were synthesized and their structural and functional properties studied. These two sequences exert a major inhibitory effect on salt-induced actin polymerization. We used circular dichroism and Fourier-transform infrared spectroscopy to show that the two synthetic peptides present some secondary structure in solution. As far as the peptide derived from the thymosin sequence was concerned, alpha-helical structure was induced by trifluoroethanol as observed with the full-length molecule. These experiments underscore the importance of the conformational state of peptide fragments in their biological activities. ELISA and fluorescence measurements have been used to identify the binding regions of these fragments to a C-terminal region (subdomain 1) of the actin sequence. Our results also emphasize the relationship between the propensity of small sequences to form secondary structures and their propensity for biological activity as related to actin interaction and inhibition of actin polymerization.

Actins↗

PubMedDate not supplied

Expression of human M2 muscarinic receptors in Sf9 cells: characterisation and reconstitution with G-proteins.

The gene for the human m2 muscarinic receptor was expressed in Sf9 cells using the baculovirus expression system. As assessed by [3H]NMS binding, Sf9 cells expressed receptor at levels of 3.3 pmoles/mg protein. The receptor was identified on western blots using an anti-muscarinic receptor antibody and was shown to have the pharmacological characteristics of an m2 muscarinic receptor. Membranes from Sf9 cells were examined to identify endogenous G-proteins by immuno-blotting and by ADP-ribosylation, indicating the presence of Gq, and a pertussis-toxin substrate which was not recognised by antibodies raised against the alpha-subunits of Gi1, Gi2, Gi3 or Go. Gsalpha was not detected, neither were there any cholera toxin substrates in Sf9 membranes. Sf9 membranes expressing m2 receptors did not show carbachol-stimulated GTPgammaS binding to endogenous G-proteins; however, when membranes were reconstituted with a mixture of purified Gi and Go, a maximum 8-fold stimulation of GTPgammaS binding was observed in response to carbachol that could be reduced by atropine. These data show that the human muscarinic m2 receptor expressed in Sf9 cells is functional.

Animals↗

PubMedDate not supplied

Expression of functional human muscarinic M2 receptors in different insect cell lines.

Human M2 receptors were expressed using the baculovirus expression system in three different insect cell lines: Sf9, Sf21 and High5. The level of expression was slightly increased in Sf21 cells versus Sf9 cells. In contrast, High5 cells were not able to produce more recombinant protein than Sf9. We also show that in both Spodoptera frugiperda cell lines a peak of expression was reached after 6 days of infection, whereas in High5 cells, the maximum of expression occurred after 3 days. Immunodetection of m2 muscarinic receptor clearly shows that the expressed protein undergoes significant proteolysis in both the Sf9 and High5 cells, whereas in the Sf21 cells this phenomenon was less detectable. Additionally, we show that in all three cell lines, the expressed recombinant receptor was functional in that it was able to stimulate GTP gamma S binding in the presence of exogenous G-proteins. Analysis of the population of G-proteins (G alpha i, G alpha o and G beta common) in Sf21 and High5 cells is provided.

Animals↗

PubMedDate not supplied

Endothelin 1: conformation and aggregation.

The features of the far UV CD spectrum of endothelin 1 (ET 1) in water-containing solutions rules out the presence of any alpha-helical contribution, thus questioning the conclusions made by several authors on the basis of NMR investigations. We propose here a structural model, based on a succession of beta turns, which is consistent with both the NMR and the CD data. Using electron microscopy, we show that ET 1 can form "micelles," and the micelles self-associate into percolation clusters which have a fractal dimension of 1.23 in a 2D space. These data, too, are in agreement with our proposed structural model.

Amino Acid Sequence↗

PubMedDate not supplied

Tissue distribution, disposition, and metabolism of cyclosporine in rats.

Tissue distribution, disposition, and metabolism of 3H-cyclosporine were studied in rats after single and repeated oral doses of 10 and 30 mg/kg and after an iv dose of 3 mg/kg. The oral doses of 10 and 30 mg/kg were dissolved in polyethylene glycol 200/ethanol or in olive oil/Labrafil/ethanol. Absorption from both formulations was slow and incomplete, with peak 3H blood levels at 3-4 hr. Approximately 30% of the radioactive dose was absorbed, which is consistent with oral bioavailability data for cyclosporine. More than 70% of the radioactivity was excreted in feces and up to 15% in urine. Elimination via the bile accounted for 10 and 60% of the oral and iv doses, respectively. Since unchanged cyclosporine predominated in both blood and tissues at early time points, the half-lives of the distribution phases (t 1/2 alpha) of parent drug and of total radioactivity were similar. In blood, kidney, liver, and lymph nodes, t 1/2 alpha of cyclosporine ranged from 6-10 hr. Elimination of radioactivity from the systemic circulation was multiphasic, with a terminal half-life of 20-30 hr. 3H-Cyclosporine was extensively distributed throughout the body, with highest concentrations in liver, kidney, endocrine glands, and adipose tissue. The concentrations of both total radioactivity and parent drug were greater in tissues than in blood, which is consistent with the high lipid solubility of cyclosporine and some of its metabolites. Skin and adipose tissue were the main storage sites for unchanged cyclosporine. Elimination half-lives were slower for most tissues than for blood and increased with multiple dosing. The amount of unchanged drug was negligible in urine and bile.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied