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F Heitz

Publications and source records attributed to F Heitz.

At least 91 records · Page 5Linked to original sources
PubMed1986

Analysis of the ion transfer through the channel of 9,11,13,15-phenylalanylgramicidin A.

The behavior of an analogue of gramicidin A in which all four tryptophanyl residues are substituted by phenylalanyl and which shows a strong voltage effect on the single channel conductance is analyzed on the basis of a 'three-barrier--two-site' model. It is shown that in the gramicidin family the side chains of some amino acids, in spite of their location, which point outside the channel can play a major role in the binding of ions in the channel and thus can significantly modify the energy profile of the channel.

Biological Transport↗
PubMed1986

Conformations of gramicidin A and its 9,11,13,15-phenylalanyl analog in dimethyl sulfoxide and chloroform.

In order to understand the difference in single channel behavior of gramicidin A as compared to that of gramicidin M- which is the mirror image of gramicidin M (all four tryptophanyl residues substituted by phenylalanine), conformational investigations were made under several experimental conditions. It is shown that, when examined under identical conditions, both molecules adopt the same conformations which could be identified in dimethyl sulfoxide (DMSO) and chloroform. In DMSO the conformation is based on a succession of beta-turns while in chloroform gramicidin A and M- can adopt a dimeric hybrid structure: a double helix terminated by two single-stranded helices involving the N- and C-terminal parts, respectively. It is therefore concluded that the difference in the energy profile between both gramicidins which was deduced from the ion transfer data has its origin in the nature of the aromatic side chains.

Chloroform↗
PubMed1986

Aggregation and ion transfer induced by tentoxin.

It is shown that tentoxin, a cyclic tetrapeptide with two N-methylated residues, is able, when added to lipid bilayers, to increase the transmembrane current through discrete events. Conformational investigations involving 1H-NMR, infrared and circular dichroism studies show that, at concentrations above 7 X 10(-5) M, the cyclic tetrapeptide aggregates in chloroform. We suggest that the aggregates could form a pore through a stacking of cycles.

Circular Dichroism↗
PubMed1985

Secondary structure of the pore-forming colicin A and its C-terminal fragment. Experimental fact and structure prediction.

Conformational investigations, using circular dichroism, on the pore-forming protein, colicin A (Mr 60 000), and a C-terminal bromelain fragment (Mr 20 000) were undertaken to estimate their secondary structure and to search for pH-dependent conformational changes. Colicin A and the bromelain peptide are mainly alpha-helical with an enrichment of the alpha-helical content in the C-terminal domain carrying the ionophoric activity. The non-negligible beta-sheet structure in the C-terminal domain is unstable and is easily transformed into alpha-helix upon decreasing the polarity of the solvent. No evidence of pH-dependent conformational modification, correlated with modification of colicin A activity, could be obtained. The secondary structure estimated on the basis of experimental data favoured a model in which the pore is built of a minimal number of six transmembrane alpha-helical segments. Search for such segments in the amino acid sequence of the C-terminal domain of colicin A was carried out by combining secondary structure prediction methods with hydrophobicity and hydrophobic movement calculations. Similar calculations on the C-terminal domains of colicin E1 and IB indicate a common structure of the pores formed by colicin A, E1 and IB. Only two or three putative transmembrane segments could be selected in the sequences of colicin A, IB or E1. As a result, it is concluded that the channel is probably not built by a single colicin molecule but more likely by an oligomer.

Chemical Phenomena↗
PubMed1985

Bacterial lipopeptides induce ion-conducting pores in planar bilayers.

Bacterial lipopeptides, known for their antibiotic activities, have been tested for their ability to interact with lipid membranes. These lipopeptides, Iturin A, Bacillomycin L and D and Peptidolipin NA present analogous structural characteristics: a heptapeptidic cycle is linked to a hydrocarbon chain. We present evidence that these lipopeptides modify the conductance of planar bilayers by forming ion-conducting pores.

Anti-Bacterial Agents↗
PubMed1985

Echocardiographic assessment of left ventricular function in patients with hypokalemia.

Based on clinical and experimental data, a cardiomyopathic syndrome has been attributed to chronic hypokalemia. Analysis of the published data indicates the presence of numerous other complicating factors which might have compromised cardiac function. Echocardiographic studies on 5 children with lifelong (Bartter's syndrome, 3 cases; congenital renal alkalosis, 1 case) or prolonged (primary hyperaldosteronism, 1 case) hypokalemia did not reveal any abnormalities of myocardial performance, thus questioning the premise that hypokalemia causes cardiomyopathy.

Bartter Syndrome↗
PubMed1985

[Plain films in supero-inferior ventricles].

Chest radiographs of 11 patients with supero-inferior ventricles proven by echocardiography and angiocardiography are presented. The main feature is the modified configuration of the left heart contour. Even if not specific, this sign is encountered frequently (72%) and may suggest the diagnosis.

Abnormalities, Multiple↗
PubMed1984

Value of systolic time intervals in the diagnosis of large patent ductus arteriosus in fluid-restricted and mechanically ventilated preterm infants.

M-mode echocardiographic features suggesting a patent ductus arteriosus are based on two groups of indirect criteria: dilation of the left cardiac cavities and changes of systolic time intervals. The reliability of the first group of criteria has been questioned in fluid-limited, mechanically ventilated preterm infants. The sensitivity of the systolic time intervals in the same circumstances is investigated. Twenty-three patients with a large patent ductus arteriosus were selected. Review of their echocardiograms shows that the sensitivity of the various criteria (expressed as percentage of positivity) was as follows: inversion of the ratio of left ventricular preejection period to right ventricular preejection period, 91.3%; left ventricular preejection period to left ventricular ejection time over right ventricular preejection period to right ventricular ejection time less than 1,83%; left atrium dilation, 74%; shortening of left ventricular preejection period, 70%; dilation of left ventricular internal dimensions in diastole, 65%; increase in left atrium/aorta, 52%; and decrease of left ventricular preejection period to left ventricular ejection time, 48%. Three criteria involving time intervals (left ventricular preejection period to right ventricular preejection period, left ventricular preejection period, and left ventricular preejection period to left ventricular ejection time) had 100% specificity. The lowest specificity was found with criteria involving the left atrium (left atrial to aortic root ratio 75% and left atrium 63%). It is concluded that study of systolic time intervals is a reliable means of detecting preterm infants with hemodynamically significant left-to-right shunt through a patent ductus arteriosus even if the infants are mechanically ventilated and fluid restricted.

Ductus Arteriosus, Patent↗
PubMed1983

Brain proteolipids. Isolation, purification and effect on ionic permeability of membranes.

Proteolipid apoproteins have been isolated from a whole bovine brain homogenate by chloroform/methanol extraction, and fractionated by chromatography on modified (lipophilic) Sephadex, followed by ion-exchange chromatography on CM-Trisacryl. The various final, highly hydrophobic, fractions are homogeneous (sodium dodecyl sulfate/polyacrylamide gel electrophoresis). Transmembrane ion transfers were studied by 22Na + flux and electrical conductance measurements. Single channel events were observed at low protein concentrations, in particular with one of the final homogeneous apoproteolipids of molecular mass 24 kDa.

Amino Acids↗
PubMed1983

Ca2+-gramicidin A interactions and blocking effects on the ionic channel.

From spectroscopic data (infrared, CD and 13C-NMR) it is shown that Ca2+ interacts with gramicidin A and that a head-to-head gramicidin A dimer can have two Ca2+-binding sites located near the COOH termini. On the basis of this result, we can propose an explanation for the blocking effect of Ca2+ on the transport of alkali metal ions (Cs+ and K+) through gramicidin channels. The binding of Ca2+ is competitive with the alkali metal ion binding; Ca2+ cannot cross the gramicidin channel and its binding in the channel is voltage dependent. From the proposed model, it is possible to account for the influence of the addition of Ca2+ on the single-channel limiting conductance and on the variation of the single-channel current as a function of the voltage in the presence of Cs+ or K+.

Calcium↗
PubMed1982

Single channels of 9, 11, 13, 15-destryptophyl-phenylalanyl-gramicidin A.

Analysis of the single-channel behavior of an analogue of gramicidin A in which all four tryptophyl residues are substituted by phenylalanyl suggests that the nature of the side chains may play an important role in the ion translocation process. Indeed, while infrared spectroscopy indicates that both peptides have very similar backbone conformations, they have different single-channel characteristics. The unit conductance of the analogue is much smaller than that of the natural product. Moreover, contrary to gramicidin A, it is voltage dependent.

Gramicidin↗