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F Heitz

Publications and source records attributed to F Heitz.

At least 73 records · Page 4Linked to original sources
PubMed1989

Ionic pores formed by cyclic peptides.

It is shown that 2 cyclic tetrapeptides, namely tentoxin and HC toxin, are able to induce the formation of transmembrane ionic channels, although a carrier mechanism could be expected on the basis of their chemical structure (presence of proline or N-methylated residues). Since other cyclic peptides but of larger size, i.e., tyrocidines, gramicidin S (decapeptides) and an octapeptide with a sequence similar to that of HC toxin, are also able to form pores, it appears that this property can be extended to a large number of cyclic peptides. A pore structure based on aggregates is proposed.

Circular Dichroism↗
PubMed1989

Gramicidin A analogs: influence of the substitution of the tryptophans by naphthylalanines.

The synthesis of 4 linear gramicidins bearing both polar and non-polar aromatic side chains is described. From the single channels data, it appears that the relative positions of these residues has little or no influence on the conductance and that this conductance is governed mainly by the number of tryptophan residues. It is also shown that the effect of the bulkiness of the apolar aromatic side chain can be neglected.

Alanine↗
PubMed1989

Single channels and surface potential of linear gramicidins.

The single channel data for 4 different linear gramicidins containing either 4 Trp, 4 Phe, 4 Tyr or TyrBzl have been analyzed on the basis of 3 barriers-2 sites model. They form 2 families which differ by their single channel behavior and thus different energy profiles of the channel. A relationship between the surface potential and the entry barrier is proposed.

Conductometry↗
PubMed1989

Conformations, cation binding, and transmembrane ion transfer properties of a cyclooctapeptide built by an alternation of D and L residues.

The conformations of a cyclic octapeptide built with an alternation of D and L residues are investigated on the basis of 1H n.m.r. and CD data. The cyclooctapeptide can form structures which are specific to the alternating D-L sequence. This peptide can form two types of complexes with cations (peptide 2-cation and peptide-cation complexes) and the binding with monovalent cation is weak. This peptide is able to induce transmembrane ion transfer through both a carrier mechanism and pore formation.

Acetonitriles↗
PubMed1989

Synthesis and ionic channels of a linear gramicidin containing naphthylalanine instead of tryptophan.

Naphthylalanine gramicidin A was prepared by the solid phase method using an aminopolyacrylic resin after optical resolution of (D, L) naphthylalanine by enzymatic methods. Removal of the peptide from the resin was achieved by transesterification of the succinic ester linkage. Infrared spectroscopy indicated that the presence of naphthylalanine strongly modifies the monomer-dimer equilibrium. Single-channel measurements suggested that the conductance of the gramicidin channel can be governed by the dipole moment of the aromatic side-chains.

1-Naphthylamine↗
PubMed1989

[Tolerability of a new non-ionic contrast medium, iopromide in x-ray computed tomography. Comparison with ioxaglate 320 mgI/ml].

Three randomized prospective and comparative trials were conducted in 165 patients undergoing brain (80) and whole body (85) CT scans. The two products compared where a new non-ionic contrast medium iopromide 300 (brain) and 370 (whole body) and the ionic low osmolar contrast medium, ioxaglate 320. Imaging quality was not different but the tolerance of the non-ionic medium was significantly better (p less than 0.05).

Contrast Media↗
PubMed1988

Peptides mimicking the flap of human renin: synthesis, conformation, and antibody recognition.

Four peptides related to human renin flap region have been synthesized. Two of them are ring closed through appropriately designed disulfide bridges. Structure analysis involving IR and NMR techniques and recognition by polyclonal human renin antibodies provides support for a beta-hairpin secondary structure of the cyclized peptides identical with that presented by the flap section in the speculative human renin model [Blundell, T., Sibanda, B. L., & Pearl, L. (1983) Nature (London) 304, 273-275; Sibanda, B. L., Blundell, T., Hobart, P. M., Fogliano, M., Bindra, J. S., Dominy, B. W., & Chirgwin, J. M. (1984) FEBS Lett. 174, 102-111].

Antibodies↗
PubMed1988

Hydrodynamic properties of colicin A. Existence of a high-affinity lipid-binding site and oligomerization at acid pH.

The hydrodynamic properties of colicin A have been studied. The molecular mass of colicin A was determined from sedimentation equilibrium centrifugation to be 63 +/- 1.2 kDa, in agreement with that determined from the primary amino acid sequence [Morlon et al. (1983) J. Mol. Biol. 110, 271-289]. The sedimentation coefficient has been analyzed over a wide range of ionic strength (NaCl 0.06-0.56 M) and pH (8-4) and was found to remain almost constant. However, below pH 5 an oligomerization of colicin A to tetramers occurred. The frictional coefficient value indicated that the shape of the colicin A monomer was very asymmetric. Analysis of the pH dependence of circular dichroism of colicin A and of its COOH-terminal domain indicated that a sharp transition occurred between pH 4 and 3. This transition was very much reduced for the COOH-terminal domain in the presence of a non-ionic detergent. The presence of a lipid-binding site in colicin A at neutral pH was demonstrated both by hydrodynamic studies with micelles of n-hexadecanoyl and n-octadecanoylphosphocholine and by differential sensitivity to a proteolytic enzyme in the presence or absence of detergent micelles. About 75 molecules of lipid were bound under these conditions suggesting that colicin A was bound to lipid micelles. In contrast, at acid pH, in the presence of an excess of lipid the tetramer was dissociated into monomers complexed to 20-30 lipid molecules, indicating the exposure of a high-affinity lipid-binding site.

Bacteria↗
PubMed1988

Mixed monolayers of linear gramicidins and phospholipid. Surface pressure and surface potential studies.

The behavior of two gramicidins incorporated into lipid monolayers is analyzed on the basis of the force and surface potential area curves. It is shown that the position of the gramicidins (helical axis parallel or perpendicular to the interface) depends on the monolayer pressure and that these molecules are not miscible with dioleoylphosphatidylcholine. Surface potential measurements suggest the existence of a relationship between the single channel characteristics and the surface potential and indicate that the tryptophans are essential for lowering the lipid surface potential in agreement with the single channel behaviour of both gramicidin A and gramicidin M.

Gramicidin↗
PubMed1988

Ionophore properties of a synthetic alpha-helical transmembrane fragment of the mitochondrial H+ ATP synthetase of Saccharomyces cerevisiae. Comparison with alamethicin.

A 22-amino acid polypeptide was synthesized to model the central transmembrane segment of subunit 8 of the H+ ATP synthetase of Saccharomyces cerevisiae and to test ionophore properties. Solid-phase synthesis was conducted on benzhydrilamino resin, and purification followed by high pressure liquid chromatography allowed the isolation of the pure product whose NH2 terminal was acetylated and whose molecular weight determined by Fast Atomic Bombardment was the expected 2,666. The infrared spectrum of this peptide in the solid state reveals a fully alpha-helical conformation, whereas in low dielectric constant solvents the alpha-helical content is 60%, as determined by circular dichroism studies. Macroscopic current-voltage curves displayed by different planar lipid bilayers (monomyristoleoyl-glycerol and phosphatidylethanolamine) doped with this peptide suggest a weakly voltage-dependent conductance. Only one conductance level is observed in any given single-channel conductance experiment. However, a series of experiments shows a distribution of conductance states, most often 440 or 3,000 pS, and occasionally 80, 1,200, or 6,500 pS. This behavior contrasts with the usual behavior of alamethicin, chosen as a model of "aggregating-helices" ionophore and whose conductance fluctuates continually between substates, through uptake and release of monomers. Nevertheless, alamethicin too can display, under certain conditions, long-lived and mono-level conductance states similar to those reported here for the newly synthesized peptide. These properties could possibly be explained by the formation of large domains of helical rods with a set of allowed and independent ionic pathways.

Alamethicin↗
PubMed1988

Left ventricular diastolic function during the first month of life.

UNLABELLED: In order to assess possible changes in myocardial relaxation occurring during the neonatal period, M-mode echocardiograms were recorded serially in 9 normal term infants and in another group of 10 one-month-old infants. The tracings were studied with an M-mode calculator. Although individual variations were greater in the data collected during the first 24 h, no significant difference was found in the indices of diastolic function of the left ventricle during the first 4 days of age. The following changes were observed between data recorded at 4 days and 1 month, respectively: normalized peak rate of left ventricle filling, 4.03 vs. 4.71 cm/s; diastolic peak velocity of early posterior motion of aortic root, 1.89 vs. 5.15 cm/s; peak velocity of left ventricle posterior wall motion in diastole, 3.31 vs. 3.50 cm/s; mitral valve EF slope, 59.05 vs. 84.92 mm/s; left ventricle isometric relaxation time, 43.88 vs. 28.50 ms. IN CONCLUSION: (1) greater individual variations are observed in indices of left ventricle diastolic function during the first day of life, and (2) significant increase in left ventricle compliance occurs during the first month of life. These changes should play a critical role in the clinical course of newborn with cardiopulmonary disease.

Diastole↗
PubMed1987

Linear gramicidins at the air-water interface.

The behavior of four linear gramicidins, which differ by the nature of their 9, 11, 13, and 15 aromatic residues, together with a covalent "head to tail" retro GA-DAla-GA dimer, has been examined at the air-water interface. It is shown that all four "monomers" have almost the same molecular area, which is compatible with either a single-stranded or a double-stranded helical model, whereas it is suggested that retro GA-DAla-GA could adopt another conformation. The surface potential measurements agree with those of different groups of molecules characterized by their single-channel behaviors.

Gramicidin↗
PubMed1987

Synthesis and characterization of Tyr(Bzl)9,11,13,15 and Tyr9,11,13,15 gramicidin A.

Tyr(Bzl) and Tyr gramicidin A were prepared by the solid phase method using a 4-(oxymethyl)-Pam resin and Bpoc as alpha-amino-protecting group. The benzylated analog [Gr.T(Bzl)] was purified by chromatography on silica gel and then on LH60 Sephadex. Removal of benzyl groups was carried out by hydrogenolysis and the debenzylated derivative (Gr.T) was purified in the same way. Both gramicidins were checked and characterized by t.l.c., HPLC, circular dichroism, 1H n.m.r. and single channel measurements. CD spectra were found to be different for Gr.T(Bzl) and Gr.T and strongly dependent upon the solvent and the concentration. Single channel conductance of Gr. T is slightly lower than that of Gr.A (A Gr.T approximately equal to 0.7 A Gr.T).

Circular Dichroism↗
PubMed1987

Cyclic tetrapeptides with sequences related to HC toxin. Conformations and cation binding.

Peptides with sequences related to HC toxin (cyclo(LAla-DAla-L-Aoe-DPro] can adopt a conformation locked by three gamma turns. A "structure--spectroscopy characteristics" relationship is proposed. These peptides can complex Mg++ cations and the binding is accompanied by a transconformation of the peptide backbone. The relevance with the biological activity of the toxin is discussed.

Amino Acid Sequence↗
PubMed1987

[Pelvimetry using x-ray computed tomography].

The accuracy and the low radiation dosage administered when tomodensitometry is carried out for pelvimetry has led us to specify the use of this technique in every day practice. We propose to make is still more reliable and to simplify it. We have correlated the measurements obtained on the ultrasound screen with those that have been obtained by measuring the dried pelvis and have sought ways of measuring directly the three fundamental diameters of the pelvis. We have achieved exact measurements within one millimeter. This very precise correlation has been reproduced when we examined skeletons using the tomodensitometer. Then, when we checked again the accuracy of these measurements, we used the method on pregnant women. We have taken two views and two slices: an AP view to study the contents of the uterus and the morphology of the upper strait; a profile view to measure the diameter between the promontory of the sacrum and posterior surface of the symphysis, and we have programmed the two following slices: a perpendicular slice at the level of the upper strait measuring directly the transverse median diameter; another slice at the level of the sciatic spines to measure directly the diameter between these spines. We present this method because it is very simple and absolutely precise and gives all the information that is necessary. The patient does not have to stay still for long and only has a small dose of irradiation. This procedure does not need the use of conversion tables, nor parallel rulers nor standardisation.

Female↗