Biomedical subjects

A Shanzer

Publications and source records attributed to A Shanzer.

28 records · Page 2Linked to original sources

PubMed1992

Vibrational CD studies of interchain hydrogen-bonded tripodal peptides.

The solution conformations of three trispeptides--L,L,L-1,3,5-C6H3[CH2NHCOCH(X)-NHBoc++ +]3, X = CH3 (Ala) or CH2CH(CH3)2 (Leu), and L,L,L-N(CH2CH2NHCOCH[CH2-CH(CH3)2]NHBoc)3--have been determined from their ir and vibrational CD (VCD) spectra in the NH stretching and carbonyl stretching regions in apolar solution. The compounds containing L-Leu are shown to occur primarily in a propeller conformation with C3 symmetry that is stabilized by interchain hydrogen bonds. Through application of the coupled oscillator model of VCD, a right-handed sense for the hydrogen-bonded chains in the propeller is deduced, in agreement with previous empirical force field calculations. The spectra also provide evidence for interchain association between two chains, resulting in a C10-ring. For chains not involved in interchain association, the spectra reveal the presence of C7-rings within a chain. The trispeptide containing L-Ala is found to occur primarily in a random form.

Amino Acid Sequence↗

PubMed1992

Monitoring of iron(III) removal from biological sources using a fluorescent siderophore.

We present here the physicochemical and biochemical properties of NBD-DFO, the 7-nitrobenz-2-oxa-1,3-diazole (NBD) derivative of the siderophore, desferrioxamine B (DFO) (Lytton et al., Mol. Pharmacol. 40, 584, 1991). Modification of DFO at its terminal amine renders it more lipophilic, imparts to it fluorescent properties, and is conservative of the high-affinity iron(III) binding capacity. NBD-DFO partitions readily from aqueous solution into n-octanol (Pcoeff = 5) and displays solvent-induced shifts in absorption and fluorescence spectra. The relative quantum yield of the probe's fluorescence increases over a 10-fold range with decreasing dielectric constant of the solvent. Fluorescence is quenched upon binding of iron(III) to the probe. We demonstrate here the application of NBD-DFO for the specific detection and monitoring of iron (III) in solutions and iron(III) mobilization from cells. Interactions between fluorescent siderophore and the ferriproteins ferritin and transferrin were monitored under physiological conditions. Iron removal from ferritin was evident by the demonstrable quenching of NBD-DFO fluorescence by scavenged iron(III). Quantitation of iron sequestered from cells by NBD-DFO or from other siderophore-iron(III) complexes was accomplished by dissociation of NBD-DFO-Fe complex by acidification and addition of excess ethylenediamin-etetraacetic acid. The sensitivity of the method and the iron specificity indicate its potential for monitoring chelatable iron under conditions of iron-mediated cell damage, iron overload, and diseases of iron imbalance such as malaria.

4-Chloro-7-nitrobenzofurazan↗

PubMed1992

Iron uptake by plants from microbial siderophores : a study with 7-nitrobenz-2 oxa-1,3-diazole-desferrioxamine as fluorescent ferrioxamine B analog.

The synthetically produced fluorescent siderophore NBD-desferrioxamine B (NBD-DFO), an analog of the natural siderophore ferrioxamine B, was used to study iron uptake by plants. Short-term (10-hour) (55)Fe uptake rates by cotton (Gossypium spp.) and maize (Zea mays L.) plants from the modified siderophore were similar to those of the natural one. In longer-term uptake experiments (3 weeks), both siderophore treatments resulted in similar leaf chlorophyll concentration and dry matter yield. These results suggest that the synthetic derivative acts similarly to the natural siderophore. The NBD-DFO is fluorescent only when unferrated and can thus be used as a probe to follow iron removal from the siderophore. Monitoring of the fluorescence increase in a nutrient solution containing Fe(3+)-NBD-DFO showed that iron uptake by plants occurs at the cell membrane. The rate of iron uptake was significantly lower in both plant species in the presence of antibiotic agent, thus providing evidence for iron uptake by rhizosphere microbes that otherwise could have been attributed to plant uptake. Confocal fluorescence microscopy revealed that iron was taken up from the complex by cotton plants, and to a much lesser extent by maize plants. The active cotton root sites were located at the main and lateral root tips. Significant variations in the location and the intensity of the uptake were noticed under nonaxenic conditions, which suggested that rhizosphere microorganisms play an important role in NBD-DFO-mediated iron uptake.

Journal Article↗

PubMed1992

Iron uptake and molecular recognition in Pseudomonas putida: receptor mapping with ferrichrome and its biomimetic analogs.

The presence of an Fe(3+)-ferrichrome uptake system in fluorescent Pseudomonas spp. was demonstrated, and its structural requirements were mapped in Pseudomonas putida with the help of biomimetic ferrichrome analogs. Growth tests, 55Fe3+ uptake, and competition experiments demonstrated that the synthetic L-alanine derivative B5 inhibits the action of ferrichrome but does not facilitate Fe3+ transport, while the enantiomeric D-Ala derivative B6 fails to compete with ferrichrome. Contraction of the molecule's envelope by replacing L-Ala by glycine provided a synthetic carrier, B9, which fully simulates ferrichrome as a growth promoter. Sodium azide inhibited 55Fe3+ uptake of the Gly derivative B9, suggesting an active transport process. These data demonstrate the chiral discrimination of the ferrichrome receptor and its sensitivity to subtle structural changes. They further confirm that receptor binding is a necessary but not sufficient condition for Fe3+ uptake to occur and suggest that binding to the receptor and transport proteins might rely on different recognition patterns.

Bacterial Outer Membrane Proteins↗

PubMed1991

Reversed siderophores act as antimalarial agents.

We describe here a family of biomimetic iron carriers that display high binding efficiency for ferric ions and favorable permeation properties across erythrocytic membranes. These carriers inhibit in vitro growth of Plasmodium falciparum by scavenging intracellular iron. The chemical features were realized by reproducing the iron-binding cavities of natural iron carriers (siderophores) and by systematic substitutions of their hydrophilic envelopes for more hydrophobic ones. In contrast to natural carriers, which participate in receptor-mediated iron uptake in cells and act as growth promoters, our synthetic carriers were designed to penetrate cellular membranes by diffusion, scavenge intracellular iron, and thereby act as growth inhibitors. Based on these properties we designate the compounds reversed siderophores and refer to the specific analogs of the natural ferrichrome as synthetic ferrichromes. The antimalarial activity of the synthetic ferrichromes correlated with their lipophilicity, and this antimalarial activity was averted when the chelators were applied as iron (III) complexes. The sites of synthetic ferrichrome action reside in the intraerythrocytic parasite and not in serum or on normal erythrocyte components. The agents were effective against all stages of parasite growth and against a variety of multidrug-resistant strains of P. falciparum. The most potent agent of this synthetic ferrichrome series, SF1-ileu, was not toxic to mammalian cells in culture and was 15-fold more potent and 20-fold faster acting than desferrioxamine. Taken in toto, these agents constitute a series of promising candidates for future use in malaria chemotherapy.

Animals↗

PubMed1991

Chiral linear hydroxamates as biomimetic analogues of ferrioxamine and coprogen and their use in probing siderophore-receptor specificity in bacteria and fungi.

Linear hydroxamate derivatives, possessing chiral alpha-amino acid moieties, were synthesized and their iron transport activities were studied in bacteria and fungi. No growth-promoting activity could be detected in the Gram-positive hydroxamate-auxotroph Aureobacterium flavescens JG9. However, Gram-negative enterobacteria, such as Escherichia coli, Pantoea agglomerans and Hafnia alvei were able to utilize iron from these analogues. Uptake of 55Fe-labeled analogues was inhibited by sodium azide, suggesting an active transport process. The receptors involved during uptake in enterobacteria were identified by using appropriate indicator organisms which are defective in the transport of either ferrioxamines (P. agglomerans FM13), coprogens (H. alvei), or both of these siderophore classes (E. coli fhuE). Our data suggest that the chiral hydroxamates are recognized by the ferrioxamine receptor (FoxA) and the coprogen receptor (FhuE) at a ratio which depends on the optical lambda/delta isomer fraction and the nature of side chains. Transport was also observed in the fungus Neurospora crassa, known to take up coprogen rather than ferrioxamines, suggesting that in this fungus the synthetic analogues behave like coprogen.

Bacteria↗

PubMed1991

Reversed siderophores as antimalarial agents. II. Selective scavenging of Fe(III) from parasitized erythrocytes by a fluorescent derivative of desferal.

We introduce here a fluorescent derivative of desferrioxamine B (DFO) that retains the high affinity of the parent compound and displays a powerful inhibition of intraerythrocytic Plasmodium falciparum growth. NBD-DFO was synthesized by coupling 7-Nitrobenz-2-oxa-1,3-diazole (NBD) to the terminal amino group of DFO. The NBD group at this position renders the DFO molecule more lipophilic and imparts to it fluorescent properties. The novel NBD-DFO probe displays a unique combination of chemical and biological properties, such as 1) improved and selective permeation properties across membranes of P. falciparum-infected erythrocytes, 2) improved efficacy as an inhibitor of intraerythrocytic P. falciparum growth (including multidrug-resistant strains), 3) demonstrable Fe3+ scavenging within parasitized red cells, and 4) usefulness as a sensitive and versatile analytical tool for quantitative assessment of Fe3+ and for following iron-scavenging processes, because the fluorescence of NBD-DFO is demonstrably quenched upon complexation with Fe3+.

4-Chloro-7-nitrobenzofurazan↗

PubMed1988

Synthetic ferrichrome analogues with growth promotion activity for Arthrobacter flavescens.

Two families of trihydroxamic acid analogues of ferrichrome were chemically synthesized and tested for biological activity with Arthrobacter flavescens. Compounds using a tertiary amine as anchor showed little activity. Several compounds using tetrahedral carbon as anchor showed activity approaching or equalling that of the natural siderophore, ferrichrome. The biological activity is discussed in relation to physical and chemical properties of the analogues.

Arthrobacter↗

PubMed1984

Enniatin B and valinomycin as ion carriers: an empirical force field analysis.

The alkali-ion binding properties of two natural depsipeptide ion carriers, enniatin B (EnB) and valinomycin (VM), are examined and compared by the empirical force field method. While VM has been shown to bind preferentially K+, Rb+, and Cs+ over Na+ in most solvents, EnB is considerably less specific. We find that EnB forms two kinds of complexes, internal and external. In internal complexes, the ion binds to all six carbonyl oxygens, while in external ones, only three oxygens, preferentially those of the D-hydroxy-isovaleryl residues, are bound. The size of the internal cavity is best suited for Na+, while K+ and Rb+ squeeze in asymmetrically by distorting the molecule, and Cs+ not at all. External binding is much less specific. Since internal complexes possess much higher strain energies than external ones, the latter may be at least as stable as the former, even in fairly non-polar solvents. VM is calculated to bind only internally, and with much less strain energy than EnB. The size of its internal cavity is well suited for binding the ions K+, Rb+, and Cs+, but is too big for Na+. The difference between the binding energies of Na+ and K+ is much smaller than that between the corresponding hydration enthalpies, thus explaining the binding preference for the latter ion.

Anti-Bacterial Agents↗

PubMed1981

A study of Li+-selective permeation through lipid bilayer membranes mediated by a new ionophore (AS701).

The neutral, noncyclic, imide and ether containing ionophore AS701, has been developed as Li+-selective molecule, to be used potentially as an aid in the Li+-therapy of manic-depressive illness. The present report is a characterization of this molecule in neutral lipid bilayer membranes. This ionophore was found to render the bilayers Li+-selective, acting as a selective carrier of monovalent cations. In addition, this molecule was found to be capable of acting as a selective carrier of monovalent anions. For both types of ions, the rate-limiting step in the process of permeation was found to be the diffusion of the carrier-ion complex through the membrane. The membrane-permeating species were found to be 2 : 1 carrier-ion complexes, carrying either a monovalent cation or a monovalent anion. The selectivity sequence among the ions studied being: Li+(1) greater than ClO4-(0.7) greater than Na+(0.07) greater than K+(0.016) greater than Rb+(0.0095) greater than Cs+(0.0083) greater than Cl-(0.001). Mg2+ and SO42- were found to be impermeant (under present experimental conditions). This sequence shows that the AS701 molecule has low selectivity for ions present in biological media, among those studied (i.e. Na+, K+, Mg2+, Cl- and SO42-). This indicates that these ions will not interfere in the Li+ permeability induced by this carrier in vivo, and that the carrier will not interfere in the normal transport processes of these ions.

Anions↗