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F Heitz

Publications and source records attributed to F Heitz.

138 records · Page 8Linked to original sources
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

The polymorphic cytochrome P-4502D6 is involved in the metabolism of both 5-hydroxytryptamine antagonists, tropisetron and ondansetron.

Tropisetron and ondansetron, which are potent and selective 5-hydroxytryptamine (5-HT3) receptor antagonists, were both metabolized by human liver microsomes to several metabolites. These metabolites include the major metabolites found in humans, which are the 5-, 6-, and 7-hydroxy tropisetron and the 7- and 8-hydroxy ondansetron. The cytochrome P-450 (CYP) 2D6 inhibitor quinidine (1 microM) reduced the hydroxylation of tropisetron (67%) and ondansetron (18%). Confirmation of CYP2D6 involvement in the hydroxylation of tropisetron and ondansetron was obtained by the formation of these metabolites in recombinant V79 cells expressing human CYP2D6. The CYP3A substrate/inhibitor, cyclosporine A (CsA) had little effect on tropisetron hydroxylation (< 10%), whereas CsA and triacetyloleandomycin reduced ondansetron 7- and 8-hydroxylation up to 27%. Substrates for CYP1A (phenacetin and acetanilide), CYP2C (mephenytoin), and CYP2E (chlorzoxazone) had negligible inhibitory effects on the hydroxylation of either tropisetron or ondansetron. For the CYP2D6-dependent O-demethylation of dextromethorphan, tropisetron and ondansetron were competitive inhibitors with Ki values of 14 and 29 microM, respectively. The CYP3A specific metabolism of CsA was also competitively inhibited by tropisetron (Ki = 2.1 mM) and ondansetron (Ki = 31 microM). Other metabolites, which are only minor in vivo were also inhibited by CsA, 47-60% for tropisetron metabolism and 43% for ondansetron metabolism. To summarize, this study has identified the involvement of CYP2D6 in the formation of the hydroxylated metabolites of tropisetron and ondansetron and in addition of CYP3A in ondansetron hydroxylation. Because these are the major pathways in vivo, coadministration of drugs competing for CYP2D6 and possibly CYP3A4 could influence the human kinetics of tropisetron and ondansetron.

Animals↗