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Biomedical subjects

A Herrmann

Publications and source records attributed to A Herrmann.

At least 109 records · Page 6Linked to original sources
PubMed1996

Prevalence of adverse reactions to food in patients with gastrointestinal disease.

The role of allergic reactions in the pathogenesis of inflammatory bowel disease and irritable bowel syndrome has been disputed. This study aimed to determine the prevalence of adverse reactions to food in patients with gastrointestinal disease. A total of 375 adult patients of a gastroenterologic outpatient clinic were examined by history, skin tests, measurements of laboratory parameters, and intestinal provocation with food allergens by colonoscopy. Some 32% complained of adverse reactions to food as a cause of their abdominal symptoms. In 14.4%, the diagnosis of intestinal food allergy could be suspected according to several criteria such as elevated total IgE, specific IgE against food antigens, eosinophilia, responsiveness to cromoglycate, and clinical signs of atopic disease. In 3.2%, the diagnosis could be confirmed by endoscopic allergen provocation and/or elimination diet and rechallenge. In conclusion, the data suggest that allergic reactions to food antigens may be a causative factor in a subgroup of patients with inflammatory and functional gastrointestinal disease.

Adolescent↗
PubMed1996

The influence of external surface potential and transmembrane potential on the passive transbilayer movement of phospholipids in the red blood cell membrane.

The passive transbilayer movement of spin-labelled analogues of phosphatidyl-choline (PC), phosphatidyl-ethanolamine (PE), and phosphatidyl-serine (PS) in red blood cell membranes was investigated at physiological and low ionic strength of the extracellular solution. Passive transbilayer movement of aminophospholipids PS and PE was measured in ATP-depleted cells. To discriminate between a possible surface potential and a transmembrane potential effect, NaCl in physiological ionic strength solution was replaced either by sucrose or by Na-tartrate (constant osmolarity). Neither in sucrose (low ionic strength) nor in Na-tartrate media a significant change of the translocation rate of the phospholipids was observed. From these results in can be concluded that changes of the external surface potential as well as of the transmembrane potential do not affect the passive transbilayer movement of phospholipids in human red blood cells.

Adenosine Triphosphate↗
PubMed1995

Structure and topology of the influenza virus fusion peptide in lipid bilayers.

The secondary structure of a 20-amino acid length synthetic peptide corresponding to the N terminus of the second subunit of hemagglutinin (HA2) of influenza virus A/PR8/34 and its interaction with phospholipid bilayers are investigated using ESR, Fourier transform infrared (FTIR), and CD spectroscopy. N-terminal spin labeling of the peptide did not affect the secondary structure of the peptide either in solution or when bound to liposomes as revealed by FTIR and CD spectroscopy. ESR spectra show that the mobility of the labeled peptide is dramatically restricted in the presence of phosphatidylcholine liposomes, suggesting a strong binding to the lipid membranes. The N terminus of the peptide penetrates into the membrane and is located within the hydrophobic core. We find an oblique insertion of the peptide into the lipid bilayer with an angle of about 45 degrees between helix axis and membrane plane using FTIR spectroscopy. No gross changes of the peptide's orientation, motion, and secondary structure were observed between pH 7.4 and pH 5.0. A model of the insertion of the fusion sequence of HA2 into a lipid bilayer is presented taking into account recent investigations on the low pH conformation of HA2 (Bullough, P. A., Hughson, F. M., Skehel, J. J., and Wiley, D. C. (1994) Nature 371, 37-43).

Amino Acid Sequence↗
PubMed1995

An improved assay for measuring the transverse redistribution of fluorescent phospholipids in plasma membranes.

The internalization of fluorescent 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD)-phospholipids from the plasma membrane can be assessed by the irreversible quenching of analogues in the outer leaflet by dithionite. Here we have utilized this assay to follow the redistribution of short-chain C6-NBD-sphingomyelin and C6-NBD-phosphatidylserine from the cell membrane of human gingiva fibroblasts. The significant uptake of dithionite across the plasma membrane and the subsequent reduction of NBD-analogues exposed to the cytoplasmic lumen does not allow an accurate measurement of the amount of internalized lipid probes even at low temperature. We could show that a precise determination can be achieved by extraction of analogues remaining in the exoplasmic half by a short pretreatment with bovine serum albumin prior to addition of dithionite. The fluorescence of those analogues localized to the cytoplasmic lumen was slowly destroyed by permeating dithionite. The fluorescence of those NBD-probes which are localized in the inner layer of intracellular vesicles remained almost unaffected in the time course of the assay. Thus, this approach allows to distinguish between different routes of internalization of NBD-phospholipids from the plasma membrane.

4-Chloro-7-nitrobenzofurazan↗
PubMed1995

Sequencing and analysis of the gene encoding the alpha-toxin of Clostridium novyi proves its homology to toxins A and B of Clostridium difficile.

A library of total Clostridium novyi DNA was established and screened for the alpha-toxin gene (tcn alpha) by hybridization with oligonucleotides derived from a partial N-terminal sequence and by using specific antisera. Overlapping subgenic tcn alpha fragments were isolated and subsequently the total sequence of tcn alpha was determined. The 6534 nucleotide open reading frame encodes a polypeptide of M(r) 250,166 and pI 5.9. The N-terminal alpha-toxin (Tcn alpha) sequence MLITREQLMKIASIP determined by Edman degradation confirmed the identity of the reading frame and the assignment of the translation start point. The toxin is not modified posttranslationally at its N-terminus nor does it consist of different subunits. Overall the amino acid sequence shows 48% homology between the Tcn alpha and both toxins A (TcdA) and B (TcdB) of Clostridium difficile. The C-terminal 382 residues of Tcn alpha constitute a repetitive domain similar to those reported for TcdA and TcdB of C. difficile. The individual repeat motifs of these three toxins consist of oligopeptides some 19-52 amino acids in length, arranged in four to five different groups. Genetic, biochemical and pharmacological data thus confirm that the three toxins belong to one subgroup, designated large clostridial cytotoxins (LCT). Further definition of their structure and detailed molecular action should allow the LCTs to be used tools for the analysis of microfilament assembly and function.

Amino Acid Sequence↗
PubMed1995

Assessment of fusogenic properties of influenza virus hemagglutinin deacylated by site-directed mutagenesis and hydroxylamine treatment.

Influenza virus hemagglutinin (HA) subtype H7 expressed from a baculovirus vector in insect cells requires cysteine residues for palmitoylation. Mutant HA devoid of fatty acids shows hemagglutinating and hemolytic activities almost identical to those of the acylated wild-type HA (wt). Using a membrane mixing assay (R18), neither the kinetics nor the pH dependence of fusion induced by wt or mutant HA was significantly different from virus-induced fusion. HA-induced fusion of insect cells with human erythrocyte ghosts could also be demonstrated by a cytoplasmic content mixing assay. Both species of recombinant HA induced the flow of lucifer yellow from preloaded ghosts into the cytoplasm of HA-bearing cells. This indicates that membrane fusion mediated by wild-type and fatty-acid-free HA includes both leaflets of the lipid bilayers. Hydroxylamine treatment of wt HA (H7) and fatty-acid-free mutant HA present in lysates of insect cells led to the complete inhibition of hemolytic activity. Deacylation of spike proteins by NH2OH treatment of virus particles resulted in a block of hemolytic activity in influenza virus subtypes H7 and H10 as well as of that in the togaviruses Semliki Forest and Sindbis virus. However, the same treatment did not affect subtypes H2 and H3 or two vesicular stomatitis virus serotypes. With such a differential effect whether or not fatty acids are present in the spike proteins of the different virus particles, hydroxylamine must have other effects than just deacylation, and therefore seems unsuitable for the study of the biological functions of acylproteins.

Acylation↗
PubMed1995

Analysis of delay times of hemagglutinin-mediated fusion between influenza virus and cell membranes.

We have studied the kinetics of low pH-induced fusion between influenza virus A/PR 8/34 and human erythrocyte membranes in suspension by using an assay based on fluorescence dequenching (FDQ) of the lipophilic dye octadecylrhodamine B chloride (R 18). As shown previously (Clague et al. 1991) the onset of FDQ is preceded by a characteristic lag time (tlag) following pH reduction. Whereas tlag represents only a subpopulation of fusing viruses with the shortest delay time we suggest here that a representative mean lag time mu lag of virus-cell fusion can be deduced from the R 18-assay. Kinetics of FDQ reflects the cumulative distribution function of lag times tau lag of single fusion events with the mean value mu lag. We show that tau lag obtained from the onset of FDQ does not always reflect the fusion behaviour of the whole population of fusing viruses. While both lag times, taulag and mu lag, exhibit a similar temperature dependence we found a significantly different dependence of both delay times on virus inactivation by low pH-pretreatment. We conclude that the mean lag time mu lag appears to be a more appropriate parameter describing the kinetics of virus-cell fusion. The analysis of delay times offers a new approach to test the validity of different kinetic models of HA-mediated fusion and to gain valuable information about HA-mediated fusion. The analysis confirms that the inactivation process proceeds via steps of the formation of the fusion pore. Although the increase of lag times can be explained by a depletion of fusion competent HA's, our data suggest that intermediate structures of HA along the inactivation pathway can still transform into a fusion site.

Cells, Cultured↗
PubMed1995

Allosteric and temperature effects on the plasma protein binding by streptococcal M protein family members.

Most group A streptococcal strains bind immunoglobulins (Ig) and fibrinogen to their cell walls. It is shown in this paper that the Ig-binding of three different strains was much weaker at 37 degrees C than at room temperature (20 degrees C), whereas the fibrinogen binding was unaffected by temperature. The binding properties and molecular sizes of two purified group A streptococcal cell surface proteins from the M protein family were studied at various temperatures, M1 protein with affinity for IgG, fibrinogen and albumin, and protein Sir22 with affinity for IgA and IgG. Both proteins appeared as monomers which bound all their ligands, including fibrinogen, very weakly at 37 degrees C, and as strongly binding dimers at 10 and 20 degrees C. Furthermore, the results demonstrated that the plasma protein binding of the bacterial proteins was allosterically regulated, i.e. the binding of a ligand to one site modulated the binding of a ligand to a second site. For example, the binding of albumin or IgG to purified M1 protein at 10 and 20 degrees C strongly enhanced the binding of fibrinogen at 37 degrees C. This indicates that the high affinity dimer form of the bacterial proteins can be stabilized at 37 degrees C, a possible explanation for the strong fibrinogen binding of whole bacteria. Finally, the sizes and binding properties of three M1 protein fragments were studied and the results indicated that the centrally located C-repeats, which are conserved among the members of the M protein family, are important for the formation of the high-affinity dimers of the bacterial proteins.

Allosteric Regulation↗
PubMed1994

Protein-dependent translocation of aminophospholipids and asymmetric transbilayer distribution of phospholipids in the plasma membrane of ram sperm cells.

We have investigated the transbilayer movement of phospholipids in the plasma membrane of ram sperm cells using spin- and fluorescence-labeled lipid analogues. After incorporation into the outer leaflet, phosphatidylcholine (PC) and sphingomyelin (SM) moved slowly to the inner cytoplasmic leaflet, whereas phosphatidylserine (PS) and phosphatidylethanolamine (PE) rapidly disappeared from the exoplasmic monolayer. Variation of the initial velocity of the relocation kinetics vs the amount of analogue incorporated into the membrane suggests a saturability of the transbilayer movement of aminophospholipids. ATP depletion or pretreatment with N-ethylmaleimide of ram sperm cells reduced the fast inward motion of PS and PE, indicating a protein-mediated aminophospholipid translocation. The results suggest for the plasma membrane of ram sperm cells the presence of an aminophospholipid translocase and an asymmetric transversal lipid distribution with aminophospholipids preferentially located in the inner leaflet and choline-containing phospholipids in the outer leaflet. The relevance of the transversal segregation of phospholipids for membrane fusion processes occurring during fertilization is discussed.

Adenosine Triphosphate↗
PubMed1994

On the validity of lipid dequenching assays for estimating virus fusion kinetics.

Octadecylrhodamine (R18) has often been used to measure membrane fusion of enveloped viruses by fluorescence dequenching. In order to see whether non-specific R18 exchange between non-fused membranes occurs we have measured fusion of influenza virus with erythrocyte membranes by utilizing dequenching of the non-exchangeable lipid analogue N-(lissamine-rhodamine B-sulfonyl)diacylphosphatidylethanolamine (N-Rh-PE). Rather low concentration of N-Rh-PE (< 0.1 mol%) were required to assess fusion since self-quenching in the influenza virus membrane was more efficient in comparison to R18. For both markers we observed the same kinetics as well as the same extent of fluorescence dequenching upon triggering low pH-induced fusion. Non-specific marker transfer was not observed. Haemolysis was not affected by either type of fluorophore. Our results confirm that R18 is a valuable tool to investigate membrane fusion of enveloped viruses in a quantitative manner. Differences in the efficiency of self-quenching of both markers are discussed.

Cytopathogenic Effect, Viral↗
PubMed1994

Incorporation of phospholipid analogues into the plasma membrane affects ATP-induced vesiculation of human erythrocyte ghosts.

The influence of various spin-labelled phospholipid analogues on the ATP-dependent vesiculation of human erythrocyte ghosts at 37 degrees C was investigated by monitoring the acetylcholinesterase activity. After incorporation of analogues into the outer leaflet a decline of endocytic vesiculation was observed. However, suppression was arrested after about 20 min when ghosts have been labelled with a phosphatidylserine analogue known to redistribute rapidly to the inner leaflet. These data suggest that vesiculation of erythrocyte ghosts is affected by differential expansion of the inner and outer leaflet.

Acetylcholinesterase↗
PubMed1994

pH-dependent binding of the fluorophore bis-ANS to influenza virus reflects the conformational change of hemagglutinin.

Binding of the fluorophore 1,1'-bis(4-anilino)naphthalene-5,5'-disulfonic acid (bis-ANS) to influenza virus A/PR 8/34 is strongly enhanced at low pH. Binding is accompanied by a significant increase in fluorescence intensity. The binding and the fluorescence increase are associated with the low-pH induced conformational change of the viral spike protein, hemagglutinin, exposing hydrophobic binding sites. The data indicate that in addition to the hydrophobic N-terminus of HA2 other hydrophobic sequences of the HA ectodomain become accessible to bis-ANS at low pH. It is shown that the time course of the fluorescence increase of bis-ANS at low pH is determined by the conformational change of HA. The application of this assay for continuously monitoring the kinetics of the structural alteration in HA is discussed and its relevance for elucidating the temporal relationship between the conformational change of HA and virus-membrane fusion is outlined.

Anilino Naphthalenesulfonates↗
PubMed1994

Kinetics of the low pH-induced conformational changes and fusogenic activity of influenza hemagglutinin.

The decrease of the intrinsic tryptophan fluorescence intensity of purified influenza (X31 strain) hemagglutinin (HA) was used to monitor the low pH-induced conformational change of this protein. The kinetics of the fluorescence decrease depended strongly on the pH. At pH optimal for fusion, the change in tryptophan fluorescence was fast and could be fitted to a monoexponential function. We measured a rate constant of 5.78 s-1 (t1/2 = 120 ms) at pH 4.9 using rapid stopped-flow mixing. Under suboptimal conditions (higher pH), the rate constant was decreased by an order of magnitude. In addition, a slow component appeared and the fluorescence decrease followed a sum of two exponentials. The kinetics of conformational changes were compared with those of the fusion of influenza virus with red blood cell membranes as assessed by the R18-dequenching assay. At optimal pH the HA conformational change was not rate-limiting for the fusion process. However, at sub-optimal pH, the slow transition to the fusogenic conformational of HA resulted in slower kinetics and decreased extent of fusion.

Animals↗
PubMed1994

Fusion between enveloped viruses and erythrocyte membranes is induced by the isoprenoid alkane pristane (2,6,10,14-tetramethylpentadecane).

Pristane (2,6,10,14-tetramethylpentadecane) is an isoprenoid alkane that induces plasma cell tumors in mice. Infection with certain retroviruses accelerates tumorigenesis but the nature of the cooperation between pristane and viruses is unknown. The purpose of this study was to investigate the potential influence of pristane on the fusion between enveloped viruses and mammalian plasma membranes. Using a fluorescence dequenching assay, we found that micromolar amounts of pristane induced fusion between erythrocyte membranes and both vesicular stomatitis virus and influenza virus. Induction of fusion occurred with as little as 5 microM pristane and reached saturation at roughly 50 microM alkane. Control experiments revealed that induction of fluorescence dequenching was not due to extraneous phenomena such as lipid transfer or non-specific interactions with the carrier for pristane (beta-cyclodextrin). Fusion was also induced by standard protocols which involve lowering the pH of the incubation medium. In the presence of pristane, low pH-triggered fusion was enhanced. The extent to which pristane induced fusion was dependent upon the orientation of the lipids in the target membrane. That is, fusion was most effective with erythrocyte ghosts which had a symmetric lipid distribution and was less effective with ghosts in which the native lipid asymmetry was maintained. Intact erythrocytes, which have an asymmetric lipid distribution, were the least effective targets. This result exactly parallels the pattern observed with acid-induced fusion. Similar patterns were also observed in the temperature dependence of fusion induced by these two protocols. The novel fusogenic activity of pristane is discussed with regard to current models of virus/membrane fusion.

Biophysical Phenomena↗
PubMed1994

[Comparative study of long-term parenteral nutrition with medium-chain and long-chain triglycerides in post-aggression metabolism].

OBJECTIVE: To determine the effect of a pure glucose and of different glucose/fat regimens as nonprotein energy source on substrate metabolism, nitrogen balance, lipoprotein pattern and liver enzymes. Long-chain and mixed long-/medium-chain triglyceride emulsions as 10 and 20% solutions were infused. DESIGN: Prospective randomized study. SETTING: General ward of a university hospital. PATIENTS: 29 patients in five groups after colorectal surgery. INTERVENTIONS: According to Harris-Benedict an amount of 150% of the calculated daily calorie intake was infused. Besides nitrogen balance and routine laboratory tests the lipoprotein pattern was examined. RESULTS: No difference was observed in protein balance, while a pathological rise of liver enzymes was mainly seen with glucose 20% and long-chain fat emulsions in a concentration of 10%. Physiological lipoprotein balance could only be achieved with a 20% solution of long-chain and medium-chain emulsions. CONCLUSIONS: The results demonstrate a fast metabolism of the MCT/LCT 20% solution with physiological lipoprotein pattern and no change in liver enzymes. High-dose glucose infusions and long-chain fat emulsions may cause a fatty degeneration of the liver, and 10% MCT/LCT emulsions may cause a rise of phospholipids and a generation of lipoprotein X.

Adult↗