Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MACROMOLECULAR SYSTEMS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources
PubMed2001

The voltage-gated Ca2+ channel is the Ca2+ sensor of fast neurotransmitter release.

Previously it demonstrated that in the absence of Ca2+ entry, evoked secretion occurs neither by membrane depolarization, induction of [Ca2+]i rise, nor by both combined (Ashery, U., Weiss, C., Sela, D., Spira, M. E., and Atlas, D. (1993). Receptors Channels 1:217-220.). These studies designate Ca2+ entry as opposed to [Ca2+]i rise, essential for exocytosis. It led us to propose that the channel acts as the Ca+ sensor and modulates secretion through a physical and functional contact with the synaptic proteins. This view was supported by protein-protein interactions reconstituted in the Xenopus oocytes expression system and release experiments in pancreatic cells (Barg, S., Ma, X., Elliasson, L., Galvanovskis, J., Gopel, S. O., Obermuller, S., Platzer, J., Renstrom, E., Trus, M., Atlas, D., Streissnig, G., and Rorsman, P. (2001). Biophys. J; Wiser, O., Bennett, M. K., and Atlas, D. (1996). EMBO J 15:4100-4110; Wiser, O., Trus, M.. Hernandez, A., Renström, E., Barg, S., Rorsman. P., and Atlas, D. (1999). Proc. Natl. Acad. Sci. U.S.A. 96:248-253). The kinetics of Ca(v)1.2 (Lc-type) and Ca(v)2.2 (N-type) Ca2+ channels were modified in oocytes injected with cRNA encoding syntaxin 1A and SNAP-25. Conserved cysteines (Cys271, Cys272) within the syntaxin 1A transmembrane domain are essential. Synaptotagmin 1, a vesicle-associated protein, accelerated the activation kinetics indicating Ca(v)2.2 coupling to the vesicle. The unique modifications of Ca(v)1.2 and Ca(v)2.2 kinetics by syntaxin 1A, SNAP-25, and synaptotagmin combined implied excitosome formation, a primed fusion complex of the channel with synaptic proteins. The Ca(v)1.2 cytosolic domain Lc(753-893), acted as a dominant negative modulator, competitively inhibiting insulin release of channel-associated vesicles (CAV), the readily releasable pool of vesicles (RRP) in islet cells. A molecular mechanism is offered to explain fast secretion of vesicles tethered to SNAREs-associated Ca2+ channel. The tight arrangement facilitates the propagation of conformational changes induced during depolarization and Ca2+-binding at the channel, to the SNAREs to trigger secretion. The results imply a rapid Ca2+-dependent CAV (RRP) release, initiated by the binding of Ca2+ to the channel, upstream to intracellular Ca2+ sensor thus establishing the Ca2+ channel as the Ca2+ sensor of neurotransmitter release.

Animals↗
PubMed1983

Two-dimensional crystallization technique for imaging macromolecules, with application to antigen--antibody--complement complexes.

Two-dimensional crystals are formed from macromolecules bound on the surface of a lipid monolayer. A ligand linked to the lipid orientates the binding, and lateral diffusion of the lipids facilitates crystallization. The crystals are suitable for structural analysis by image processing of electron micrographs. An example is the formation of ordered arrays of antibodies on a monolayer of a lipid hapten, and subsequent decoration of these arrays with the first component of complement. Image processing indicates the arrangement of antibodies and the site of complement binding. This approach should be widely applicable to molecular complexes, such as those in replication, protein synthesis, hormone-receptor interaction and metabolic processes.

Antigen-Antibody Complex↗
PubMed2003

Challenges for the oral delivery of macromolecules.

The rapid integration of new technologies by the pharmaceutical industry has resulted in numerous breakthroughs in the discovery, development and manufacturing of pharmaceutical products. In particular, the commercial-scale production of high-purity recombinant proteins has resulted in important additions to treatment options for many large therapeutic areas. In addition to proteins, other macromolecules, such as the animal-derived mucopolysaccharide heparins, have also seen dramatic growth as injectable pharmaceutical products. To date, macromolecules have been limited as therapeutics by the fact that they cannot be orally delivered. This article will address the current status and future possibilities of oral macromolecular drug delivery.

Administration, Oral↗
PubMed1979

Multiplicity of molecules carrying blood-group-I antigen on erythrocyte membranes.

A human serum containing a monoclonal anti-(blood-group I) antibody was used to investigate the distribution of blood-group-I antigen on erythrocyte membrane components. Sodium dodecyl sulphate/polyacrylamide-gel-electrophoresis profiles of immuneprecipitates by using 3H-labelled (by the galactose oxidase/NaB3H4 method) and 125I-labelled solubilized stroma were compared. Different radioactive profiles were revealed by the two radiolabelling methods. In the immunoprecipitates the predominant 125I radioactivity within the gel had the electrophoretic mobility of Band-3 protein (apparent mol.wt. 90 000--100 000), whereas the 3H radioactivity revealed a diffusely migrating component(s) (apparent mol.wt. range 40 000--70 000) in addition to radioactivity compatible with glycolipids at the dye front. The diffusely migrating 3H-labelled component was shown to have a similar electrophoretic mobility to a subpopulation of erythrocyte poly(glycosyl)ceramides with blood-group-I activity.

Blood Group Antigens↗
PubMed2003

Effects of osmolarity, ions and compatible osmolytes on cell-free protein synthesis.

To mimic what might happen in cells exposed to hypertonicity, the effects of increased osmolarity and ionic strength on cell-free protein synthesis have been examined. Translation of globin mRNA by rabbit reticulocyte lysate decreased by 30-60% when osmolality was increased from 0.35 to 0.53 osmol/kg of water by the addition of NaCl, KCl, CH(3)CO(2)Na or CH(3)CO(2)K. In contrast, equivalent additions of the compatible osmolytes betaine or myo -inositol caused a 40-50% increase in the rate of translation, whereas amino acids (50-135 mM) that are transported via system A had no significant effect. Addition of 75 mM KCl caused a dramatic fall in the amount of the 43 S pre-initiation complex, whereas it was totally preserved when osmolarity was similarly increased by the addition of 150 mM betaine. The formation of a non-enzymic initiation complex between rabbit [(3)H]Phe-tRNA, poly(U) and the 80 S ribosomes was unaffected by the addition of 75 mM NaCl or KCl, but translation of the complex decreased by 70%. Density-gradient centrifugation of reticulocyte extracts translating endogenous mRNA revealed that addition of 150 mM betaine had no effect, whereas addition of 75 mM KCl caused a marked decrease in the polysome peak, concomitant with an increase in the proportion of 80 S ribosomes and ribosomal subunits, even when elongation was inhibited with fragment A of diphtheria toxin. These results are consistent with the notion that both initiation and elongation are inhibited by unusually high concentrations of inorganic ions, but not by the compatible osmolytes betaine or myo -inositol.

Amino Acids↗
PubMed2005

Towards nanomedicine with a supramolecular approach: a review.

A review dedicated mainly to the results obtained by the authors on the use of cyclodextrin (CD) derivatives on protein (enzyme) stabilization through covalent and non-covalent interactions (host-guest supramolecular interactions) is presented here. This latter procedure served to introduce a new method for enzyme immobilization on metallic surfaces that can be used to prepare biosensors and therapeutic nanodevices. The surfaces of gold (and silver) electrodes and nanoparticles were modified with sulphur-containing cyclodextrin derivatives. The protein (enzyme) was then supramolecularly immobilized on the modified surface when one or more of its bulky hydrophobic moieties was included into the CD cavity. The protein can also be modified with a typical CD guest, such as adamantane, to achieve a more stable immobilization. Different examples are presented, such as a biosensor based on monolayers of adamantane-modified cytochrome c and a bienzymatic nanodevice comprising gold nanoparticles stabilized with CD associated to catalase and superoxide dismutase modified with complementary host-guest residues. The possibilities of this new approach for the development of biosensors and therapeutic nanodevices are analyzed.

Biosensing Techniques↗
PubMed1981

Crystalline arrays of membrane-bound acetylcholine receptor.

Electron micrographs of tubular structures with a crystalline arrangement of membrane-bound acetylcholine receptor oligomers have been analyzed by digital image reconstruction. The receptor molecules are oriented synaptic side out, and in projection they appear to be asymmetric and have a defined orientation. All four subunits are contained in the oligomers as demonstrated by immunoelectron microscopy; these structures therefore appear to be suitable for subunit localization in the oligomer.

Animals↗
PubMed1981

In vitro synthesis, glycosylation, and membrane insertion of the four subunits of Torpedo acetylcholine receptor.

We have characterized the early biosynthetic forms of the Torpedo electroplax acetylcholine receptor by using a cell-free protein synthesizing system. We obtained primary translation products of approximately 38, 50, 49, and 60 kilodaltons for the alpha, beta, gamma, and delta polypeptides, respectively, by using immunoprecipitation with subunit-specific antisera. These chains could each be labeled by the formylated initiator [35S]Met-tRNA. On cotranslational incubation with pancreatic rough microsomes, glycosylated forms of each subunit were obtained that had molecular weights close to those of their mature authentic counterparts. Extensive trypsinization reduced the glycosylated forms of the receptor subunits to glycosylated membrane-protected fragments of approximately 35 (alpha), 37 (beta), 45 (gamma), and 44 (delta) kilodaltons. In this system, then, each receptor chain spans the membrane at least once. This in vitro-synthesized material apparently exhibited neither oligomeric assembly nor alpha-bungarotoxin binding.

Animals↗
PubMed1982

Ultrastructure of the membrane attack complex of complement: detection of the tetramolecular C9-polymerizing complex C5b-8.

The ultrastructure of the membrane attack complex (MAC) of complement had been described as representing a hollow cylinder of defined dimensions that is composed of the proteins C5b, C6, C7, C8, and C9. After the characteristic cylindrical structure was identified as polymerized C9 [poly(C9)], the question arose as to the ultrastructural identity and topology of the C9-polymerizing complex C5b-8. An electron microscopic analysis of isolated MAC revealed an asymmetry of individual complexes with respect to their length. Whereas the length of one boundary (+/- SEM) was always 16 +/- 1 nm, the length of the other varied between 16 and 32 nm. In contrast, poly(C9), formed spontaneously from isolated C9, had a uniform tubule length (+/- SEM) of 16 +/- 1 nm. On examination of MAC-phospholipid vesicle complexes, an elongated structure was detected that was closely associated with the poly(C9) tubule and that extended 16-18 nm beyond the torus of the tubule and 28-30 nm above the membrane surface. The width of this structure varied depending on its two-dimensional projection in the electron microscope. By using biotinyl C5b-6 in the formation of the MAC and avidin-coated colloidal gold particles for the ultrastructural analysis, this heretofore unrecognized subunit of the MAC could be identified as the tetramolecular C5b-8 complex. Identification also was achieved by using anti-C5 Fab-coated colloidal gold particles. A similar elongated structure of 25 nm length (above the surface of the membrane) was observed on single C5b-8-vesicle complexes. It is concluded that the C5b-8 complex, which catalyzes poly(C9) formation, constitutes a structure of discrete morphology that remains as such identifiable in the fully assembled MAC, in which it is closely associated with the poly(C9) tubule.

Complement C9↗
PubMed1987

Purification to homogeneity and enzymological characterization of a functional covalent complex composed of cytochromes P-450 isozyme 2 and b5 from rabbit liver.

A covalent complex between rabbit hepatic microsomal cytochromes P-450 isozyme 2 (LM2) and b5 was created and purified to greater than 95% homogeneity. The purified complex was largely comprised of the two cytochromes covalently attached at the interface of the functional electron transfer-effector complex as shown by the following evidence. The spin state of the LM2 within the complex was greater than the spin state of free LM2, and the addition of free cytochrome b5 (cyt b5) did not further increase the spin state of the LM2 within the complex. The spectral binding parameters (Kd and delta Amax) for the association of benzphetamine with LM2 in the complex were identical to those observed with free LM2 in the presence of saturating concentrations of free cyt b5 and much different from those observed for LM2 in the absence of cyt b5. Reconstituted monooxygenase activity of the covalent LM2-cyt b5 complex (LM2-cyt b5) in the presence of NADPH-cytochrome P-450 reductase was much higher than the activity of free LM2 and approached the activity of free LM2 in the presence of optimal concentrations of free cyt b5. Furthermore, the Km for the flavoprotein in supporting either free LM2 or LM2-cyt b5-dependent p-nitroanisole demethylation were similar. (iv) Less than 20-25% of the cyt b5 within the complex could be reduced by free NADH-cytochrome b5 reductase (NADH-cyt b5 reductase) albeit at a slow rate. The implications of this data to the current understanding of the mechanism and stoichiometry of protein interactions in the hepatic mixed function oxidase system are discussed.

Animals↗
PubMed2005

Thermotolerance and virulence of Aspergillus fumigatus: role of the fungal nucleolus.

The ability to thrive at 37 degrees C is characteristic of all human pathogens and has long been suspected to play a role in the pathogenesis of aspergillosis. As a thermotolerant fungus, Aspergillus fumigatus is capable of growth at temperatures that approach the upper limit for all eukaryotes, suggesting that the organism has evolved unique mechanisms of stress resistance that may be relevant to its ability to adapt to the stress of growth in the host. High temperature is a strain on many biological systems, particularly those involved in complex macromolecular assemblies such as ribosomes. This review will discuss the relationship between thermotolerance and virulence in pathogenic fungi, emphasizing the link to ribosome biogenesis in A. fumigatus. Future work in this area will help determine how rapid growth is accomplished at elevated temperature and may offer new avenues for the development of novel antifungals that disrupt thermotolerant ribosome assembly.

Aspergillosis↗
PubMed1998

Assessment of high-affinity hybridization, RNase H cleavage, and covalent linkage in translation arrest by antisense oligonucleotides.

Antisense oligonucleotides (ONs) are designed to hybridize target mRNA in a sequence-specific manner and inhibit gene expression by preventing translation, either by activation of RNase H or steric blockage of the ribosome complex. Second-generation ONs, which possess greater binding affinity for target RNA relative to the isosequential phosphodiester (PO) ONs, have been developed and include, among others, peptide nucleic acids (PNA) and N3' P5' phosphoramidate oligonucleotides (npONs). In the present study, PNA and npON derivatives were targeted to the coding portion of the complementary mRNA of the N protein of the vesicular stomatitis virus (VSV) in order to evaluate their ability to arrest translation in an in vitro rabbit reticulocyte lysate system. High-affinity hybridization of ONs lacking RNase H activity was not sufficient to block translation in this test system. Only antisense ONs acting via an RNase H mechanism or by steric hindrance through covalent attachment (via transplatin modification) to the target mRNA were found to definitively arrest translation in this study.

Animals↗
PubMed1986

The terminal complement complex in sera deficient in the eighth component of complement (C8).

The terminal complement complex (TCC) was quantified in sera from patients with a genetic deficiency of C8 alpha-gamma or C8 beta. The individual sera contained only trace amounts of TCC compared with a normal serum pool. The content of TCC increased after mixing the two sera, which was consistent with reconstitution of C8 activity. Only a moderate increase in TCC was obtained after zymosan activation of the individual sera, whereas activation of the mixture resulted in high amounts of TCC. C8 was demonstrated in the TCC of both deficient sera. These results may indicate that functional C8 is present in trace amounts despite the genetic deficiency, and that the terminal pathway may function to some extent although not enough to be detectable in less sensitive assays.

Antibodies, Monoclonal↗
PubMed1980

Energy-linked reactions catalyzed by the purified ATPase complex (F0F1) from Rhodospirillum rubrum chromatophores.

1. The isolation of F0F1-ATPase complex from Rhodospirillum rubrum chromatophores by the use of taurodeoxycholate is described. 2. The enzyme preparation contains about 12 polypeptides; five are subunits of the F1 moiety. 3. The ATPase activity of the purified enzyme is dependent on the addition of phospholipids. 4. Km-vales for Mg2+-ATP and Ca2+-ATP are similar to the values obtained for the membrane-bound enzyme. 5. The F0F1-ATPase complex is more than 70% inhibited by oligomycin and N,N'-dicyclohexylcarbodiimide. 6. The F0F1-ATPase complex was integrated into liposomes. The reconstituted proteoliposomes catalyzed energy transduction as shown by ATP-dependent quenching of acridine dye fluorescence and ATP-32Pi exchange.

Adenosine Triphosphatases↗