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Background: Medullary Thyroid Carcinoma (MTC) is closely associated with mutations in the RET proto-oncogene, placing the activated RET protein at the center of MTC pathogenesis. Existing therapeutic solutions, primarily tyrosine kinase inhibitors such as selpercatinib, vandetanib, and cabozantinib, have shown moderate efficacy but are accompanied by increased risks of side effects and resistance. This study unveils a promising avenue using nonactin, a compound historically recognized for its antibacterial properties, targeting the G-quadruplex interactions within the RET proto-oncogene. Method: In this research, high-throughput screening was conducted using a luciferase reporter-based cellular assay. The MTC TT cell line was treated with nonactin for 24 and 48 h. Immunoblotting and RT-PCR were employed to measure the protein and RNA levels of RET and its downstream stream proteins. Binding to the G-Quadruplex was assessed using melting curves and Circular Dichroism. The cell cycle was analyzed using FACS, and caspase activity was measured to indicate the activation of apoptosis. Results: Nonactin was identified to significantly reduce luciferase activity driven by the RET promoter. A deeper exploration revealed nonactin's remarkable selectivity against tumor cell lines harboring RET mutations, effectively inducing apoptosis. Nonactin was also found to bind to the G-quadruplex region on RET. Conclusion: The findings highlight the compound's therapeutic potential, emphasizing its mechanism of inducing apoptosis in active mutant RET cell lines by interacting with G-quadruplex structures. This novel insight opens avenues for a potentially effective treatment for MTC, potentially bypassing the challenges associated with current TKIs. [ABSTRACT FROM AUTHOR]

Nonactin is a non‐enantiomorphous (S4 symmetric), optically active natural product with a specific rotation of zero in solutions at all frequencies and temperatures. All optically active, non‐enantiomorphous natural products have specific rotations of zero as a consequence of the spatial average of bisignate chiroptical (magnetoelectric or gyration) tensors with equal and opposite eigenvalues. Zeros that arise in the spatial average are distinct in principle, though not necessarily in practice, from zeros that arise in optical inactivity—chiroptical tensors with zero values for all elements as in centric molecules. Nonactin would be measurably optically active when oriented. The anisotropy of the optical activity of nonactin and its cation complexes, likewise S4 symmetric, are studied here by computation to emphasize the infelicitous linkage between optical activity and chirality. Computations show that changes in the conformation of the nonactin macrocycle upon complexation principally are responsible for diminishing the computed optical activity; the metals are incidental. [ABSTRACT FROM AUTHOR]

Silk, traditionally acclaimed as the “queen of fiber,” has been widely used thanks to its brilliant performance such as gentleness, smoothness and comfortableness. Owing to its mechanical characteristics and biocompatibility silk has a definitive role in biomedical applications, both as fibroin and fabric. In this work, the simultaneous dyeing and functionalization of silk fabric with pigments from Streptomyces anulatus BV365 were investigated. This strain produced high amounts of orange extracellular pigments on mannitol-soy flour agar, identified as actinomycin D, C2 and C3. The application of purified actinomycins in the dyeing of multifiber fabric was assessed. Actinomycins exhibited a high affinity towards protein fibers (silk and wool), but washing durability was maintained only with silk. Acidic condition (pH5) and high temperature (65°C) facilitated the silk dyeing. The morphologies and chemical components of the treated silk fabrics were analyzed using scanning electron microscopy and Fourier transform infrared spectroscopy. The results showed the pigments bind to the silk through interaction with the carbonyl group in silk fibroin rendering the functionalized, yet surface that does not cause skin irritation. The treated silk exhibited a remarkable antibacterial effect, while the biocompatibility test performed with 3D-reconstructed human epidermis model indicated safe biological properties, paving the way for future application of this material in medicine.

Streptomycetes produce a huge variety of bioactive metabolites, including antibiotics, enzyme inhibitors, pesticides and herbicides, which offer promise for applications in agriculture as plant protection and plant growth-promoting products. The aim of this report was to characterize the biological activities of strain Streptomyces sp. P-56, previously isolated from soil as an insecticidal bacterium. The metabolic complex was obtained from liquid culture of Streptomyces sp. P-56 as dried ethanol extract (DEE) and possessed insecticidal activity against vetch aphid (Medoura viciae Buckt.), cotton aphid (Aphis gossypii Glov.), green peach aphid (Myzus persicae Sulz.), pea aphid (Acyrthosiphon pisum Harr.) and crescent-marked lily aphid (Neomyzus circumflexus Buckt.), as well as two-spotted spider mite (Tetranychus urticae). Insecticidal activity was associated with production of nonactin, which was purified and identified using HPLC-MS and crystallographic techniques. Strain Streptomyces sp. P-56 also showed antibacterial and antifungal activity against various phytopathogenic bacteria and fungi (mostly for Clavibacfer michiganense, Alternaria solani and Sclerotinia libertiana), and possessed a set of plant growth-promoting traits, such as auxin production, ACC deaminase and phosphate solubilization. The possibilities for using this strain as a biopesticide producer and/or biocontrol and a plant growth-promoting microorganism are discussed. [ABSTRACT FROM AUTHOR]

The biological activity of the macrocycle nonactin is intimately related to its ionophore properties and ability to act as a selective cation carrier. The competitive binding of small protonated amines constitutes a particularly key issue in the biochemistry of nonactin, which finds application in sensing and extraction technologies. In this study, isolated complexes of nonactin with ammonium and hydroxylammonium are investigated with infrared action spectroscopy and quantum chemical computations. The focus of the investigation is on the coordination achieved by the protonated guest with the oxygen atoms of either the oxolane groups or the carboxyl groups in the ester linkages of the macrocyle host and their relative contributions to the stability of the complexes. The experimental and computational data converge to a preferred coordination arrangement associated with a tight binding of the N—Hδ+ bonds with the oxolane groups. In the N H 4 + complex, this results in a compact complex of S4 symmetry. In contrast, symmetry is disrupted in the NH3OH+ complex, as it incorporates a bifurcated coordination of the —OH bond with a carbonyl group and an oxolane group of the host, involving also a more stretched arrangement of the nonactin backbone. These gas-phase conformations are in agreement with the structures postulated for these complexes in condensed phases, from previous Raman and crystallographic experiments. [ABSTRACT FROM AUTHOR]

• A novel real-time flow automatic system with NH 4 +-ISFET sensor was reported. • It offered excellent performance, a wide linear range, high sensitivity, and long lifetime. • It successfully determined NH 4 + in aquaculture water samples. • It can be monitored online anywhere and anytime using internet-connected devices. Aquaculture systems necessitate vigilant monitoring of water quality parameters to ensure optimal conditions for aquatic life. Ammonium ion (NH 4 +) concentration stands as one of the critical factors, influencing the health and productivity of aquatic organisms. This study focuses on the development and implementation of a real-time flow automatic system, utilizing ion-sensitive field-effect transistor (ISFET) technology for the precise detection of ammonium ions in aquaculture settings. The proposed system integrates ISFET sensors within a flow automatic system to enable continuous and automated monitoring of NH 4 + concentrations in aquaculture ponds or systems. The ion-selective membrane (ISM) on a printed circuit board was prepared by drop casting a mixture of nonactin as an ammonium ionophore and poly(vinyl chloride- co -vinyl acetate- co -vinyl alcohol) and dioctyl sebacate to create an NH 4 +-ISFET sensor. The limit of detection was found to be 0.06 mg L−1 with a linear range of 0.1 – 1000.0 mg L−1 and an R2 of 0.9986 at a sensitivity of 61.29 mV dec−1. The NH 4 +-ISFET sensor had a useful lifetime of more than 8 months. Leveraging the high sensitivity and rapid response capabilities of the ISFET sensors, the system facilitates instantaneous detection and real-time quantification of ammonium levels and allows monitoring of ammonium concentrations anywhere and anytime using internet-connected devices. This proposed system emphasizes the significance of the real-time ISFET monitoring system to enhance water quality in aquaculture while mitigating the risks associated with fluctuating ammonium levels in aquatic environments. [Display omitted] [ABSTRACT FROM AUTHOR]

Streptomycetes produce a huge variety of bioactive metabolites, including antibiotics, enzyme inhibitors, pesticides and herbicides, which offer promise for applications in agriculture as plant protection and plant growth-promoting products. The aim of this report was to characterize the biological activities of strain Streptomyces sp. P-56, previously isolated from soil as an insecticidal bacterium. The metabolic complex was obtained from liquid culture of Streptomyces sp. P-56 as dried ethanol extract (DEE) and possessed insecticidal activity against vetch aphid (Medoura viciae Buckt.), cotton aphid (Aphis gossypii Glov.), green peach aphid (Myzus persicae Sulz.), pea aphid (Acyrthosiphon pisum Harr.) and crescent-marked lily aphid (Neomyzus circumflexus Buckt.), as well as two-spotted spider mite (Tetranychus urticae). Insecticidal activity was associated with production of nonactin, which was purified and identified using HPLC-MS and crystallographic techniques. Strain Streptomyces sp. P-56 also showed antibacterial and antifungal activity against various phytopathogenic bacteria and fungi (mostly for Clavibacfer michiganense, Alternaria solani and Sclerotinia libertiana), and possessed a set of plant growth-promoting traits, such as auxin production, ACC deaminase and phosphate solubilization. The possibilities for using this strain as a biopesticide producer and/or biocontrol and a plant growth-promoting microorganism are discussed.

Streptomyces symbionts in insects have shown to be a valuable source of new antibiotics. Here, we report the genome sequence and the potential for antibiotic production of "Streptomyces sp. M54", an Actinobacteria associated with the eusocial wasp, Polybia plebeja. The Streptomyces sp. M54 genome is composed of a chromosome (7.96 Mb), and a plasmid (1.91 Kb) and harbors 30 biosynthetic gene clusters for secondary metabolites, of which only one third has been previously characterized. Growth inhibition bioassays show that this bacterium produces antimicrobial compounds that are active against Hirsutella citriformis, a natural fungal enemy of its host, and the human pathogens Staphylococcus aureus and Candida albicans. Analyses through TLC-bioautography, LC–MS/MS and NMR allowed the identification of five macrocyclic ionophore antibiotics, with previously reported antibacterial, antitumor and antiviral properties. Phylogenetic analyses placed Streptomyces sp. M54 in a clade of other host-associated strains taxonomically related to Streptomyces griseus. Pangenomic and ANI analyses confirm the identity of one of its closest relatives as Streptomyces sp. LaPpAH-199, a strain isolated from an ant-plant symbiosis in Africa. In summary, our results suggest an insect-microbe association in distant geographic areas and showcase the potential of Streptomyces sp. M54 and related strains for the discovery of novel antibiotics. [ABSTRACT FROM AUTHOR]

Annexins are proteins that bind lipids in the presence of calcium. Though multiple functions have been proposed for annexins, there is no general agreement on what annexins do or how they do it. We have used the well-studied conductance probes nonactin, alamethicin, and tetraphenylborate to investigate how annexins alter the functional properties of planar lipid bilayers. We found that annexin XII reduces the nonactin-induced conductance to approximately 30% of its original value. Both negative lipid and approximately 30 microM Ca(2+) are required for the conductance reduction. The mutant annexin XIIs, E105K and E105K/K68A, do not reduce the nonactin conductance even though both bind to the membrane just as wild-type does. Thus, subtle changes in the interaction of annexins with the membrane seem to be important. Annexin V also reduces nonactin conductance in nearly the same manner as annexin XII. Pronase in the absence of annexin had no effect on the nonactin conductance. But when added to the side of the bilayer opposite that to which annexin was added, pronase increased the nonactin-induced conductance toward its pre-annexin value. Annexins also dramatically alter the conductance induced by a radically different probe, alamethicin. When added to the same side of the bilayer as alamethicin, annexin has virtually no effect, but when added trans to the alamethicin, annexin dramatically reduces the asymmetry of the I-V curve and greatly slows the kinetics of one branch of the curve without altering those of the other. Annexin also reduces the rate at which the hydrophobic anion, tetraphenylborate, crosses the bilayer. These results suggest that annexin greatly reduces the ability of small molecules to cross the membrane without altering the surface potential and that at least some fraction of the active annexin is accessible to pronase digestion from the opposite side of the membrane.

Many factors regulate the expression of specialised secondary metabolite biosynthetic gene clusters, which have been recognised as important for the discovery of novel microbial natural products. A cosmid library based on genomic DNA of the marine-derived Streptomyces puniceus Act1085 was constructed and screened to identify a short gene cluster similar to the nonactin biosynthetic cluster. The ORFs of the gene cluster isolated had high amino acid sequence identity, from 82% to 96%, with corresponding ORFs of the nonactin biosynthetic gene cluster from S . griseus subsp. griseus ETH A7796. Despite the expectation that nonactin or its derivatives would be made from heterologous expression of the gene cluster found in S . albus J1074, nocardamine was isolated. The heterologous expression data indicate that the production of nocardamine in S . albus J1074 is due to an ortholog of nonG , a TetR family transcriptional regulator, from S . puniceus Act1085. [ABSTRACT FROM AUTHOR]

Background/aim: Primary effusion lymphoma (PEL) is classified as a rare non-Hodgkin's B-cell lymphoma that is caused by Kaposi's sarcoma-associated herpesvirus (KSHV); PEL cells are latently infected with KSHV. PEL is frequently resistant to conventional chemotherapies. Therefore, the development of novel therapeutic agents is urgently required. Nigericin, a H + and K + ionophore, possesses unique pharmacological effects. However, the effects of nigericin on PEL cells remain unknown., Materials and Methods: We examined the cytotoxic effects of the K + ionophores, nigericin, nonactin, and valinomycin, on various B-lymphoma cells including PEL. We also evaluated ionophore-induced changes in signaling pathways involved in KSHV-induced oncogenesis. Moreover, the effects of nigericin on mitochondrial membrane potential and viral reactivation in PEL were analyzed., Results: Although the three tested ionophores inhibited the proliferation of several B-lymphoma cell lines, nigericin inhibited the proliferation of PEL cells compared to KSHV-negative cells. In PEL cells, nigericin disrupted the mitochondrial membrane potential and caused the release of cytochrome c, which triggered caspase-9-mediated apoptosis. Nigericin also induced both an increase in phosphorylated p38 MAPK and proteasomal degradation of β-catenin. Combination treatment of nigericin with the p38 MAPK inhibitor SB203580 potentiated the cytotoxic effects towards PEL cells, compared to either compound alone. Meanwhile, nigericin did not influence viral replication in PEL cells., Conclusion: Nigericin induces apoptosis in PEL cells by mitochondrial dysfunction and down-regulation of Wnt/β-catenin signaling. Thus, nigericin is a novel drug candidate for treating PEL without the risk of de novo KSHV infection., (Copyright © 2023 International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Here we report the production of the cyclic macrotetrolide nonactin from the fermentation culture of Streptomyces griseus subsp. griseus. Nonactin is a member of a family of naturally occurring cyclic ionophores known as the macrotetrolide antibiotics. Our fermentation procedure of Streptomyces griseus was performed at 30 °C and 200 rev·min−1 for 5 days on a rotary shaker. Diaion HP-20 and Amberlite XAD-16 were added to the fermentation medium. Isolated yield of nonactin was up to 80 mg·L−1 using our methodology. Nonactin is commonly known as an ammonium ionophore and also exhibits antibacterial, antiviral, and antitumor activities. It is also widely used for the preparation of ion-selective electrodes and sensors. Chemical synthesis of nonactin has been achieved by some groups; however, overall yields are very low, making efficient biosynthesis an attractive means of production. [ABSTRACT FROM AUTHOR]

The ionophore antibiotic nonactin permeabilizes cell membranes to [ABSTRACT FROM AUTHOR]

In continuation of our ongoing search for bioactive compounds from microbial extracts, we performed antiproliferative and/or antimalarial assays on extracts of 806 microbial species isolated from Madagascan marine organisms, on 1317 species isolated from Madagascan soil samples and on a Streptomyces species ( S . 4 ) from a marine sponge collected from the Florida Keys. This work identified active extracts from four Streptomyces isolates ( S . 1 , S . 2 , S . 3 and S . 4 ). The extracts of Streptomyces S . 1 and S . 2 showed antiproliferative activity against the A2780 ovarian cancer cell line, while those of S . 3 and S . 4 displayed both antiproliferative and antimalarial activity. Bioassay-guided fractionation coupled with dereplication of the active extracts led to the identification and isolation of nonactin ( 1 ), monactin ( 2 ), dinactin ( 3 ), ±-nonactic acid ( 4 ), toyocamycin ( 5 ), piperafizine A ( 6 ) and a new dipeptide named xestostreptin ( 7 ). The structures of all isolated compounds 1 – 7 were elucidated by analyses of their NMR spectroscopic and mass spectrometric data, and were confirmed by comparison with the data reported in the literature. Compound 6 was crystallized and subjected to X-ray diffraction analysis to confirm its structure as piperafizine A ( 6 ). Compounds 1 – 3 displayed strong antiproliferative activity against A2780 ovarian cancer cells (IC 50 values of 0.1, 0.13 and 0.2 μM, respectively), A2058 melanoma cells (IC 50 values of 0.2, 0.02 and 0.02 μM, respectively), and H522-T1 non small-cell cancer lung cells (IC 50 values of 0.1, 0.01 and 0.01 μM, respectively), while compounds 4 and 7 exhibited weak antiplasmodial activity against the Dd2 strain of Plasmodium falciparum , with IC 50 values of 6.5 and 50 μM, respectively. [ABSTRACT FROM AUTHOR]

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibriumoccurring in the two-phase water–nitrobenzene system (1= nonactin, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logKex(Ag+,1 ⋅ Na+) = 0.6 ± 0.1. Furthermore, the stability constant of the1 ⋅ Ag+complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb(1 ⋅ Ag+) = 6.6 ± 0.2. Finally, employing quantum mechanical calculations, the most probable structure of the cationic complex species1 ⋅ Ag+was derived. In the resulting complex, having a tennis-ball-seam conformation with theC2symmetry, the ‘central’ cation Ag+is bound by eight relatively strong bonding interactions to eight oxygen atoms of the parent nonactin ligand. The interaction energy of the considered1 ⋅ Ag+complex was found to be –468.5 kJ/mol, confirming also the formation of this cationic species. [ABSTRACT FROM PUBLISHER]

Actinomycetes, especially those belonging to the genus Streptomyces, are economically important from a biotechnological standpoint: they produce antibiotics, anticancer compounds and a variety of bioactive substances that are potentially applicable in the agrochemical and pharmaceutical industries. This paper combined accurate-mass electrospray tandem mass spectrometry in the full scan and product ion scan modes with compounds library data to identify the major compounds in the crude extract produced by Streptomyces sp. AMC 23; it also investigated how sodiated nonactin ([M + Na]+) fragmented. Most product ions resulted from elimination of 184 mass units due to consecutive McLafferty-type rearrangements. The data allowed identification of four macrotetrolides homologous to nonactin (monactin, isodinactin, isotrinactin/trinactin and tetranactin) as well as three related linear dimer compounds (nonactyl nonactoate, nonactyl homononactoate and homononactyl homononactoate). The major product ions of the sodiated molecules of these compounds also originated from elimination of 184 and 198 mass units. UPLC-MS/MS in the neutral loss scan mode helped to identify these compounds on the basis of the elimination of 184 and 198 mass units. This method aided monitoring of the relative production of these compounds for 32 days and revealed that the biosynthetic process began with increased production of linear dimers as compared with macrotetrolides. These data could facilitate dereplication and identification of these compounds in other microbial crude extracts. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The development and analytical characterization of a novel ion-selective potentiometric cell in a temporary-transfer tattoo platform for monitoring ammonium levels in sweat is presented. The fabrication of this skin-worn sensor, which is based on a screen-printed design, incorporates all-solid-state potentiometric sensor technology for both the working and reference electrodes, in connection to ammonium-selective polymeric membrane based on the nonactin ionophore. The resulting tattooed potentiometric sensor exhibits a working range between 10−4 M to 0.1 M, well within the physiological levels of ammonium in sweat. Testing under stringent mechanical stress expected on the epidermis shows that the analytical performance is not affected by factors such as stretching or bending. Since the levels of ammonium are related to the breakdown of proteins, the new wearable potentiometric tattoo sensor offers considerable promise for monitoring sport performance or detecting metabolic disorders in healthcare. Such combination of the epidermal integration, screen-printed technology and potentiometric sensing represents an attractive path towards non-invasive monitoring of a variety of electrolytes in human perspiration. [ABSTRACT FROM AUTHOR]

Ammonia is a toxic nitrogenous waste product of amino acid metabolism that may accumulate to high levels in the medium ingested by larvae of the fruit fly Drosophila melanogaster. Here we report measurements of haemolymph NH4+ concentration and the secretion of NH4+ by the Malpighian (renal) tubules. Measurement of NH4+ concentrations in secreted droplets is complicated either by the requirement for large sample volumes for enzymatic assays or by the inadequate selectivity of NH4+-selective microelectrodes based on nonactin. We have developed a novel liquid membrane NH4+-selective microelectrode based on a 19- membered crown compound (TD19C6), which has been used previously in ammonium-selective macroelectrodes. In conjunction with an improved technique for correcting for interference of potassium, NH4+-selective microelectrodes based on TD19C6 permit accurate measurement of ammonium concentration in haemolymph samples and nanolitre droplets of fluid secreted by the Malpighian tubules of D. melanogaster. The results indicate that active secretion of ammonium into the Malpighian tubule lumen is sufficient to maintain concentrations of ~1mmol l-1 ammonium in the haemolymph of larvae reared on diets containing 100 mmol l-1 ammonium chloride. [ABSTRACT FROM AUTHOR]

Surveyed in this account are the syntheses of nocardiolactone, valilactone, nonactin, pamamycin 621A, and IKD-8344 performed by our group. The key step of these formations is intramolecular O-alkylation involving positions extremely liable to β- elimination under conventional alkylation conditions. 1 Introduction 2 Nocardiolactone 3 Valilactone 4 Nonactin 5 Pamamycin 621A 6 IKD-8344 7 Summary [ABSTRACT FROM AUTHOR]

Abstract: (R)-1-(1-Naphthyl)ethanol is an essential chiral substrate for the synthesis of nonactin and dihydro-[1H]-quinoline-2-one derivatives. Stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-1-(1-naphthyl)ethanol by whole cell biocatalysis, using Candida parapsilosis, is reported here. Candida parapsilosis possesses a requisite redox system for the stereoinversion of secondary alcohol. The reaction conditions (temperature, time, pH, organic solvent, etc.) significantly influenced the stereoinversion process. Optimum conditions were found to be the reaction temperature of 30°C, a cellmass concentration of 200mg/mL, pH 7 (phosphate buffer, 50mM), a shaking speed of 200rpm, and a 12h reaction time. Under these optimum conditions, (R)-1-(1-naphthyl)ethanol was obtained in 100% eeR and 88% yield. [Copyright &y& Elsevier]

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium $$ {\text{M}}^{ + } \left( {\text{aq}} \right) \, + {\mathbf{1}}\cdot{\text{Na}}^{ + } \left( {\text{nb}} \right) \Leftrightarrow {\mathbf{1}}\cdot{\text{M}}^{ + } \left( {\text{nb}} \right) \, + {\text{Na}}^{ + } \left( {\text{aq}} \right) $$ taking place in the two-phase water-nitrobenzene system $$ \begin{gathered} ({\text{M}}^{ + } = {\text{ Li}}^{ + } ,{\text{ K}}^{ + } ,{\text{ Rb}}^{ + } ,{\text{ Cs}}^{ + } ,{\text{ H}}_{ 3} {\text{O}}^{ + } ,{\text{NH}}_{4}^{ + }, {\text{ Ag}}^{ + } ,{\text{ Tl}}^{ + } ;{\mathbf{1}} \hfill \\ = {\text{ nonactin}};{\text{ aq }} = {\text{ aqueous phase}},{\text{ nb }} = {\text{nitrobenzene phase}}) \hfill \\ \end{gathered} $$ were determined. Moreover, the stability constants of the 1·M complexes in water-saturated nitrobenzene were calculated; they were found to increase in the series of $$ {\text{Cs}}^{ + } < {\text{ Rb}}^{ + } < {\text{ H}}_{ 3} {\text{O}}^{ + } ,{\text{ Ag}}^{ + } < {\text{ Tl}}^{ + } < {\text{ Li}}^{ + } < {\text{ K}}^{ + } < {\text{NH}}_{4}^{ + } $$. [ABSTRACT FROM AUTHOR]

Abstract: From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium taking place in the two-phase water-nitrobenzene system (A− =picrate, 1 =nonactin; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as log K ex(1·Sr2+, 2A−)=−2.0±0.1. Further, the stability constant of the 1·Sr2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25°C: log β nb (1·Sr2+)=7.1±0.1. Finally, by using DFT calculations, the most probable structure of the cationic complex species 1·Sr2+ was derived. In the resulting complex having S 4 symmetry, the “central” cation Sr2+ is bound by eight relatively strong bond interactions to eight oxygen atoms of the parent nonactin ligand 1. [Copyright &y& Elsevier]

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs(aq) + A(aq) + 1(nb) ⇔ 1·Cs(nb) + A(nb) taking place in the two-phase water-nitrobenzene system (A = picrate, 1 = nonactin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ( 1·Cs,A) = 2.8 ± 0.1. Further, the stability constant of the 1·Cs complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β ( 1·Cs) = 4.7 ± 0.1. Finally, by using quantum-mechanical DFT calculations, the most probable structure of the resulting cationic complex species 1·Cs was derived. [ABSTRACT FROM AUTHOR]

The urease enzyme of Helicobacter pylori was isolated from biopsy sample obtained from antrum big curvature cell extracts. A new urea biosensor was prepared by immobilizing urease enzyme isolated from Helicobacter pylori on poly(vinylchloride) (PVC) ammonium membrane electrode by using nonactine as an ammonium ionophore. The effect of pH, buffer concentration, and temperature for the biosensor prepared with urease from H. pylori were obtained as 6.0, 5 mM, and 25 °C, respectively. We also investigated urease concentration, stirring rate, and enzyme immobilization procedures in response to urea of the enzyme electrode. The linear working range of the biosensor extends from 1 × 10 to 1 × 10 M and they showed an apparent Nernstian response within this range. Urea enzyme electrodes prepared with urease enzymes obtained from H. pylori and Jack bean based on PVC membrane ammonium-selective electrode showed very good analytical parameters: high sensitivity, dynamic stability over 2 months with less decrease of sensitivity, response time 1-2 min. The analytical characteristics were investigated and were compared those of the urea biosensor prepared with urease enzyme isolated from Jack bean prepared at the same conditions. It was observed that rapid determinations of human serum urea amounts were also made possible with both biosensors. [ABSTRACT FROM AUTHOR]

A mimic of a plausible biosynthetic intermediate of bisho­mononactic acid, one of the monomers of macrotetrolide antibiotics (polynactin), was synthesized as a thiol ester. FAB-MS analysis showed that fermentation of polynactin producing Streptomyces griseus with the compound, afforded the unnatural polynactins containing bishomononactic acid(s). [ABSTRACT FROM AUTHOR]

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M(aq) + 1 · Sr(nb) ⇔ 1 · M(nb) + Sr(aq) taking place in the two-phase water-nitrobenzene system (M = Mg, Ca, Ba, Cu, Zn, Pb, Mn, Ni; 1 = nonactin; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1 · M complexes in nitrobenzene saturated with water were calculated; they were found to increase in the following order: Mg, Mn < Ba, Cu, Zn, Ni < Sr < Ca < Pb. [ABSTRACT FROM AUTHOR]

We have been interested in the application of readily available, fermentation-derived natural products as key building blocks for the preparation of natural product-like libraries rich in structural and stereochemical diversity. In this manuscript we describe the conversion of methyl nonactate, derived from nonactin, to a diversable scaffold characteristic of macrolide natural products. The synthesis features a key ring-closing metathesis reaction to form the macrocycle. [ABSTRACT FROM AUTHOR]

Nonactin is a polyketide antibiotic produced by Streptomyces griseus ETH A7796 and is an ionophore that is selective for K+ ions. It is a cyclic tetraester generated from two monomers of (+)-nonactic acid and two of (-)-nonactic acid, arranged (+)-(-)-(+)-(-) so that nonactin has S4 symmetry and is achiral. To understand why achiral nonactin is the naturally generated diastereoisomer, we generated two alternate diastereoisomers of nonactin, one prepared solely from (+)-nonactic acid and one prepared solely from (-)-nonactic acid, referred to here as 'all-(+)-nonactin' and 'all-(-)-nonactin', respectively. Both non-natural diastereoisomers were 500-fold less active against Gram positive organisms than nonactin confirming that the natural stereochemistry is necessary for biological activity. We used isothermal calorimetry to obtain the Ka, ΔG, ΔH, and ΔS of formation for the K+, Na+, and NH4+ complexes of nonactin and all-(-)-nonactin; the natural diastereoisomer bound K+ 880-fold better than all-(-)-nonactin. A picrate partitioning assay confirmed that all-(-)-nonactin, unlike nonactin, could not partition K+ ions into organic solvent. To complement the thermodynamic data we used a simple model system to show that K+ transport was facilitated by nonactin but not by all-(-)-nonactin. Modeling of the K+ complexes of nonactin and all-(-)-nonactin suggested that poor steric interactions in the latter complex precluded tight binding to K+. Overall, the data show that both enantiomers of nonactic acid are needed for the formation of a nonactin diastereoisomer that can act as an ionophore and has antibacterial activity [ABSTRACT FROM AUTHOR]

The article presents a comparative analysis of the large conformational change of the pseudomerohedrally twinned monoclinic structure of unfolded free nonactin upon the encapsulation of alkali metal ions. It observes the presence of symmetry-independent half-molecules of nonactin in the asymmetric unit residing on a crystallographic two-fold axis during crystallization. Also observed is the low-temperature high-precision ordered structure of free nonactin possessing an unfolded and more planar geometry but globular when encapsulating a cation.

This work presents a new sensor for ammonium determination based on interdigitated conductometric thin-film planar electrodes. It was fabricated by including nonactin in a plasticised poly(vinyl chloride) membrane deposited on the sensitive area of the transducer. The effects of pH, buffer concentration, the interferences of Na+, K+ and Ca2+ ions, the effect of ionic strength and of temperature were investigated. The linear working range and sensitivity of the biosensor were also determined. The sensitivity of the ammonium detection was around 6.2 µS µM-1 [image omitted] and the detection limit was 2 × 10-5 M. The biosensor exhibits the advantages of a simple fabrication procedure, good sensor-to-sensor reproducibility, wide dynamic range and good storage stability (12 weeks). [ABSTRACT FROM AUTHOR]

Abstract: We describe the phenomenon of mechanoelectrical transduction in macroscopic lipid bilayer membranes modified by two cation-selective ionophores, valinomycin and nonactin. We found that bulging these membranes, while maintaining the membrane tension constant, produced a marked supralinear increase in specific carrier-mediated conductance. Analyses of the mechanisms involved in mechanoelectrical transduction induced by the imposition of a hydrostatic pressure gradient or by an amphipathic compound chlorpromazine reveal similar changes in the charge carrier motility and carrier reaction rates at the interface(s). Furthermore, the relative change in membrane conductance was independent of membrane diameter, but was directly proportional to the square of membrane curvature, thus relating the observed phenomena to the bilayer bending energy. Extrapolated to biological membranes, these findings indicate that ion transport in cells can be influenced simply by changing shape of the membrane, without a change in membrane tension. [Copyright &y& Elsevier]

New ammonium-selective membrane electrode based on poly(vinyl chloride) (PVC) membrane containing palmitic acid (a long-chain fatty acid) and nonactin as an ammonium ionophore for the determination of ammonim ions in the 10 -7 - 10 -1 mol/L concentration range was prepared and compared to those of the electrode prepared by using carboxylated PVC. Sebacate was used as a plasticiser for both of the ammonium sensor membranes. The analytical characteristics of the ammonium electrodes was investigated. The effect of pH, buffer concentration, temperature and stirring rate on the response to ammonium electrode was investigated. The linear working range and sensitivity of the electrodes were also determined. Ammonium electrodes give Nernstian response (52–58 mV/p[NH 4 + ]) throughout the ammonium ion concentration range of 10 -1 to 10 -6 M with detection limits of 10 -6 M ammonium ions. The ammonium-selective electrodes prepared by using the PVC membranes containing palmitic acid showed more effective performance than those of the carboxylated PVC. The ammonium ion sensor has potential application in the analysis of ammonium ions for biosensor construction. [ABSTRACT FROM AUTHOR]

A new urea biosensor was prepared by immobilizing urease with four different procedures on poly(vinylchloride) (PVC) ammonium membrane electrode containing palmitic acid by using nonactine as an ammonium-ionophore. The analytical characteristics were investigated and were compared those of the biosensor prepared by using carboxylated PVC. The effect of pH, buffer concentration, temperature, urease concentration, stirring rate and enzyme immobilization procedures on the response to urea of the enzyme electrode were investigated. The linear working range and sensitivity of the biosensor were also determined. The urea biosensor prepared by using the PVC membranes containing palmitic acid showed more effective performance than those of the carboxylated PVC based biosensors. Additionally, urea assay in serum was successfully carried out by using the standard addition method. [ABSTRACT FROM AUTHOR]

Discusses the effect of thallium ions on the isolated mitochondria of rat liver in the presence of nonactin. Factors which lead to mitochondrial swelling and shrinkage; Cause of energy dissipation on the inner mitochondrial membrane; Impact of ionophore valinomycin on the permeability of the inner mitochondrial membrane.

Plasticised poly(vinyl chloride) optode membrane incorporated with nonactin as ionophore, ETH 5294 as H+-selective chromoionophore and potassium tetrakis(4-chlorophenyl)borate as anionic site, was used as a reversible sensing device for indirect determination of nicotine. Nicotine was extracted from cigarette samples and converted to its bromoethane derivative (ND+Br−) by reacting with a solution of bromoethane in ethanol. ND+Br−, in a solution of Tris (hydroxymethyl)aminomethane–HCl buffer, was extracted into the bulk of the optode membrane and subsequently caused changes in optical absorption of the sensing layer. The pH effect, response mechanisms, response behaviour, response time, dynamic working range, detection limit, sensitivity and selectivity were discussed in detail. [Copyright &y& Elsevier]

Nonrespiring rat-liver mitochondria swell in media containing high concentrations of thallous nitrate, indicating passive penetration of TI+ This swelling could be further stimulated by 10 nM or more nonactin while even 1μM valinomycin was without effect. Nonactin was also much more potent than valinomycin in stimulating swelling of respiring mitochondria in the presence of thallous acetate. It is evident that nonactin acts as a potent lonophore of TI + able to promote both the passive and energized uptake of TI + in mitochondria. The distribution of TI+, present in trace concentrations below 1 mM, was measured during energisation by respiration both in the presence and absence of ionophores. Respiration induced net uptake of TI+ only in the presence of lonophores, though TI + as a permeant cation was expected to sense respiration-induced changes in the membrane potential. The data may be interpreted as indicating that no transmembrane potential is formed upon energisatiom, but localized fields, which are able to interact with the lipophilic ionophore complexes of TI +, but not with the hydrophilic cation Tl+ This interpretation is valid only if thermodynamic equilibrium has been reached. [ABSTRACT FROM AUTHOR]

The effects of methylation on the rate constants of carrier-mediated ion transport have been studied on monooleindecane bilayers with K, Rb, NH, and TI ions, using the series of homologue carriers, nonactin, monactin, dinactin, trinactin, and tetranactin, each member of the series differing from the previous one by only one methyl group. Measurements of the amplitude and time constant of the current relaxation after a voltage jump over a large domain of voltage and permeant ion concentration, together with a computer curve-fitting procedure, have allowed us, without the help of steady-state current-voltage data, to deduce and compare the values of the various rate constants for ion transport: formation ( k) and dissociation ( k) of the ion-carrier complex at the interface, translocation across the membrane interior of the carrier ( k) and the complex ( k). With the additional information from steady-state low-voltage conductance measurements, we have obtained the value of the aqueous phase-membrane and torus-membrane partition coefficient of the carrier ({ie191-1} and {ie191-2}). From nonactin to tetranactin with the NH ion, k, and {ie191-3} are found to increase by factors of 5 and 3, respectively, k and {ie191-4} to decrease respectively by factors 8 and 2, while k and k are practically invariant. Nearly identical results are found for K, Rb, and Tl ions. k, k and k are quite invariant from one ion to the other except for Tl where k is about five times larger. On the other hand, k depends strongly on the ion, indicating that dissociation is the determining step of the ionic selectivity of a given carrier. The systematic variations in the values of the rate constants with increasing methylation are interpreted in terms of modifications of energy barriers induced by the carrier increasing size. Within this framework, we have been able to establish and verify a fundamental relationship between the variations of k and k with methylation. [ABSTRACT FROM AUTHOR]

The kinetics of Na+ and K+ transport across the membrane of large unilamellar vesicles (LUV) were determined at two pH's when transport was induced by (221)C10-cryptand (diaza-1,10-decyl-5-pentaoxa-4,7,13,16,21-bicyclo [8.8.5.] tricosane) at various temperatures, and by nonactin at 25 degrees C and (222)C10-cryptand at 20 and 25 degrees C. The rate of Na+ and K+ transport by (221)C10 saturated with the cation and carrier concentrations. Transport was noncooperative and exhibited selectivity for Na+ with respect to K+. The apparent affinity of (221)C10 for Na+ was higher and less pH-dependent than that for K+, and seven times higher than the affinity for Na+ of nonactin. Its enthalpy was higher than that of (222)C10 for K+ ions (20.5 vs. 1.7 kcal . mole-1). The efficiency of (221)C10 transport of Na+ was pH- and carrier concentration-dependent, and was similar to that of nonactin; its activation energy was similar to that for (222)C10 transport of K+ (35.5 and 29.7 kcal . mole-1, respectively). The reaction orders in cation n(S) and in carrier m(M), respectively, increased and decreased as the temperature rose, and were both independent of carrier or cation concentrations; in most cases, they varied slightly with the pH. n(S) varied with the cation at pH 8.7 and with the carrier for Na+ transport only, while m(M) always depended on the type of cation and carrier. Results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes. [ABSTRACT FROM AUTHOR]