Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Polymerization”

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 667 records · Page 37Linked to original sources
PubMed2005

Engineering polysaccharide-based polymeric micelles to enhance permeability of cyclosporin A across Caco-2 cells.

PURPOSE: To assess and compare the effectiveness of two types of polysaccharide-based micelles as delivery vehicles for poorly water soluble drugs by monitoring their permeability across Caco-2 cell monolayers. METHODS: Dextran (DEX) and hydroxypropylcellulose (HPC) were hydrophobically modified (HM) by grafting polyoxyethylene cetyl ether (POE-C16, 15 mol% and 5.4 mol%, respectively). The onset of micellization and mean diameter of polymeric micelles formed by HM-DEX and HM-HPC were determined by fluorescence spectroscopy and dynamic light scattering, respectively. Cyclosporin A (CsA)-loaded polymeric micelles were prepared by a dialysis procedure, and the amount of incorporated CsA was assayed by high performance liquid chromatography (HPLC). The stability of micelles in simulated gastric and intestinal fluids was studied as a function of contact time, and their cytotoxicity toward Caco-2 cells was evaluated using the MTT colorimetric assay. The bidirectional transport across Caco-2 cell monolayers of CsA entrapped in HM-DEX and HM-HPC micelles and of the polymers themselves was evaluated in the presence and absence of P-glycoprotein inhibitor. RESULTS: The amount of CsA incorporated in HM-HPC and HM-DEX micelles reached 5.5 and 8.5% w/w, respectively (entrapment efficiency of 22% or more). The polymeric micelles exhibited high stability in gastric and intestinal fluids and no significant cytotoxicity toward Caco-2 cells. The apical to basal permeability of CsA across Caco-2 cells increased significantly when loaded in polymeric micelles compared to free CsA. CONCLUSIONS: Polysaccharide-based polymeric micelles are promising carriers for the oral delivery of poorly water soluble drugs. In vitro tests indicate that, overall, HM-HPC micelles are more effective compared to HM-DEX micelles.

Biological Transport↗
PubMed2004

Stable expression of 1Dx5 and 1Dy10 high-molecular-weight glutenin subunit genes in transgenic rye drastically increases the polymeric glutelin fraction in rye flour.

We generated and characterized transgenic rye synthesizing substantial amounts of high-molecular-weight glutenin subunits (HMW-GS) from wheat. The unique bread-making characteristic of wheat flour is closely related to the elasticity and extensibility of the gluten proteins stored in the starchy endosperm, particularly the HMW-GS. Rye flour has poor bread-making quality, despite the extensive sequence and structure similarities of wheat and rye HMW-GS. The HMW-GS 1Dx5 and 1Dy10 genes from wheat, known to be associated with good bread-making quality were introduced into a homozygous rye inbred line by the biolistic gene transfer. The transgenic plants, regenerated from immature embryo derived callus cultures were normal, fertile, and transmitted the transgenes stably to the sexual progeny, as shown by Southern blot and SDS-PAGE analysis. Flour proteins were extracted by means of a modified Osborne fractionation from wildtype (L22) as well as transgenic rye expressing 1Dy10 (L26) or 1Dx5 and 1Dy10 (L8) and were quantified by RP-HPLC and GP-HPLC. The amount of transgenic HMW-GS in homozygous rye seeds represented 5.1% (L26) or 16.3% (L8) of the total extracted protein and 17% (L26) or 29% (L8) of the extracted glutelin fraction. The amount of polymerized glutelins was significantly increased in transgenic rye (L26) and more than tripled in transgenic rye (L8) compared to wildtype (L22). Gel permeation HPLC of the un-polymerized fractions revealed that the transgenic rye flours contained a significantly lower proportion of alcohol-soluble oligomeric proteins compared with the non-transgenic flour. The quantitative data indicate that the expression of wheat HMW-GS in rye leads to a high degree of polymerization of transgenic and native storage proteins, probably by formation of intermolecular disulfide bonds. Even gamma-40k secalins, which occur in non-transgenic rye as monomers, are incorporated into these polymeric structures. The combination 1Dx5 + 1Dy10 showed stronger effects than 1Dy10 alone. Our results are the first example of genetic engineering to significantly alter the polymerization and composition of storage proteins in rye. This may be an important step towards improving bread-making properties of rye whilst conserving its superior stress resistance.

Chromatography, High Pressure Liquid↗
PubMed1983

The effect of ATP concentration on the rate of actin polymerization.

It was found that the rate of polymerization of G-actin increased with the decrease of ATP concentration. When excess ATP was replaced by chloride through anion-exchange treatment, the extent of actin polymerization did not change provided that the ionic strength was raised immediately after the treatment. In the meantime, the rate of actin polymerization was greatly enhanced after the removal of excess ATP. The rate enhancement was much less when both excess Ca2+ and excess ATP were removed. G-actin with excess ATP replaced by chloride had larger light scattering and showed a "catalytic" effect on the polymerization of normal G-actin. The inhibition of actin polymerization by cytochalasin B in 100 mM KCl was much more obvious for G-actin with excess ATP removed than for normal G-actin. It is suggested that the reduction of excess ATP concentration in a G-actin solution increases the binding of weak-affinity Ca2+ and promotes the formation of oligomeric actin (actin nuclei).

Actins↗
PubMed1985

Entropy-driven polymerization of ribgrass virus protein.

Holmes ribgrass virus (HRV), because of serological results, is regarded as a distantly related strain of tobacco mosaic virus (TMV). HRV protein differs substantially in amino acid sequence from TMV protein, especially in that it contains one histidine residue and three methionine residues, compared to none of either for TMV protein. Ultracentrifugation and hydrogen ion titration data on HRV protein, similar to those obtained previously for the early stage polymerization of TMV and E66 proteins, demonstrated some similarities and more distinct differences from those of the other two proteins. The major similarities are that the early polymerization of HRV protein is entropy driven and the first major polymerized product is a 20 S component, presumably a double disk or two-turn helix, as in the case of the other proteins. The major differences are that the unpolymerized HRV protein sediments at 3 S rather than at the 4 S for the others; it is presumably a dimer of the polypeptide chain. The enthalpy of polymerization per mole of A protein, delta H*, is 18,400 cal for HRV protein, compared to about 30,000 for TMV protein. One mol of H+ ion/mol HRV A protein, compared to 1.5 for TMV and E66 proteins, is bound during polymerization to the 20 S state. Contrasted with the other proteins, very little if any electrical work contribution was detected for the HRV protein. A major difference was found in hydrogen ion titration. Unpolymerized HRV protein binds hydrogen ions significantly in the unpolymerized A protein state, unlike the A proteins from the other two viruses.

Hydrogen Bonding↗
PubMed1991

Highly variable effects of beryllium and beryllium fluoride on tubulin polymerization under different reaction conditions: comparison of assembly reactions dependent on microtubule-associated proteins, glycerol, dimethyl sulfoxide, and glutamate.

Carlier et al. (1988, Biochemistry 27, 3555-3559; 1989, Biochemistry 28, 1783-1791) described enhancement of tubulin polymerization and stabilization of glycerol-induced microtubules by BeF3- (by addition of both BeSO4 and NaF to reaction mixtures). We were able to confirm the stabilization of glycerol-induced polymer reported by these workers, provided Mg2+ was also present in the reaction. When we examined polymerization dependent on microtubule-associated proteins (MAPs), however, we obtained very different results. BeF3- had no significant effect on this reaction, or the polymer formed, under any condition examined. Lower concentrations of BeSO4 alone, in contrast to a negligible effect in glycerol, enhanced polymerization with MAPs provided the concentrations of both Mg2+ and GTP were low; and Be2+ stabilized the polymer, if the GTP concentration was low, at both low and high Mg2+ concentrations. Higher concentrations of BeSO4 precipitated tubulin, an effect which was not affected by Mg2+, partially prevented but not reversed by MAPs, and prevented or reversed by either NaF or nucleotides at adequate concentrations. These results suggest that Be2+ binds at site(s) distinct from Mg2+ site(s), and that partial occupancy of these site(s) at lower Be2+ concentrations enhances tubulin polymerization and polymer stability, while extensive occupancy at higher Be2+ concentrations results in tubulin precipitation. Effects of Be2+ and BeF3- on polymerization dependent on dimethyl sulfoxide or glutamate were also evaluated. The dimethyl sulfoxide system displayed properties similar to those of the glycerol system, while the glutamate system was similar to the MAPs system.

Animals↗
PubMed1988

Mutual recognition between polymerized liposomes: enzyme and enzyme inhibitor system.

In order to examine the usefulness of polymerized liposomes as a model for cell membranes, a mutual recognition phenomenon between different liposomes on which complementary ligands were attached was examined. We used trypsin- and soybean trypsin inhibitor (STI)-carrying polymerized liposomes to attain high sensitivities. The STI which was immobilized on the polymerized mono-dienoylphosphatidylcholine liposome showed a definite inhibitory effect on the catalytic activity of the trypsin which was immobilized on another polymerized liposome, whereas the inhibitory effect of the STI which was immobilized on the di-dienoylphosphatidylcholine liposome was much smaller than that of the mono-dienoylphosphatidylcholine system because of the larger rigity of the di-dienoylphosphatidylcholine liposome. These results suggest that the mutual recognition between complementary ligands can be realized by using polymerized liposomes with a physical stability and moderate deformability as their carriers.

Cell Communication↗
PubMed1971

The extraction of polymeric collagen from biopsies of human skin.

1. Medium sized biopsies (100 mm2) of human skin from 14 subjects yielded sufficient polymeric collagen for depolymerisation and ultrastructural investigations. 2. The yields obtained from one skin specimen by the alpha-amylase, EDTA and lyotropic relaxation (water) methods of extracting polymeric collagen are similar. 3. The responses to depolymerisation treatments of the three polymeric collagen samples extracted by each of the three methods from one skin specimen are cross-correlated. There are however electron microscopical differences between the three polymeric collagen samples. 4. The results show that it feasible to study the polymeric collagen of normal and diseased human skin from medium sized biopsies.

Adult↗
PubMed1975

A neutral protease in rheumatoid synovial fluid capable of attacking the telopeptide regions of polymeric collagen fibrils.

Fluorescent-labelled polymeric collagen fibrils have been prepared which contain three fluoresein residues in the telopeptide regions and four fluorescein residues in the helical region of each tropocollagen unit within the polymer. This material has been used as a substrate for the study of enzymes present in the synovial fluid of inflamed rheumatoid joints which are capable of degrading polymeric collagen fibrils. Two enzyme systems were observed, one inhibited by EDTA and having the properties of the known synovial collagenase, the other having the properties of a neutral protease. The neutral protease was found to be present in sonicates of the polymorphonuclear leucocytes in the synovial fluids of inflamed joints. This enzyme attacked the telopeptides of fluorescein-labelled polymeric collagen fibrils and was similar to trypsin in removing two residues of fluorescein-labelled peptides per tropocollagen molecule within the polymeric collagen fibrils but did not depolymerise the polymeric collagen fibrils.

Animals↗
PubMed1978

Photooxidation of fibrinogen in the presence of methylene blue and its effect on polymerization.

Human fibrinogen was illuminated in the presence of methylene blue. The resulting photooxidized fibrinogen was devoid of polymerization activity and thrombin-induced coagulability. The initial rate of the thrombin catalysed release of fibrinopeptides from photooxidized fibrinogen was normal. It was shown that illumination of photooxidized fibrinogen and photooxidized fragment N-DSK caused the modification of histidine residues. Tryptophan residues were also modified. When fibrinogen was photooxidized immediately after the addition of thrombin, the capacity to polymerize was lost. The inhibition of polymerization was less marked when oxidation was initiated at the time when polymerization began or thereafter. Photooxidized fibrinogen acts as an inhibitor of the polymerization of fibrin monomers. Photooxidized fibrinogen has affinity for thrombin-activated fibrinogen-Sepharose and thrombin-activated fragment N-DSK-Sepharose. When the former conjugate is illuminated in the presence of methylene blue its affinity for fibrinogen is decreased. It is concluded that the fragment N-DSK domain of fibrinogen is affected by photooxidation.

Amino Acids↗
PubMed1983

The tightly bound divalent cation regulates actin polymerization.

The polymerization characteristics of Ca++-actin and Mg++-actin were studied by measuring initial rates of polymerization upon addition of phalloidin-stabilized nuclei and neutral salt. Under conditions where the effects of divalent cation exchange were minimized, CaCl2 and MgCl2 were found to be equally effective in polymerizing actin. Mg++-actin was found to nucleate and polymerize more readily than Ca++-actin, having a forward rate constant about twice that of Ca++-actin under a variety of polymerizing conditions. The critical concentration for Ca++-actin is approximately 20 times that for Mg++-actin under equivalent conditions. These data imply that the polymer of Mg++-actin must be more stable than that of Ca++-actin, having a depolymerization rate constant about 10 fold lower. Since Mg++ is probably the tightly-bound cation in vivo, whereas Ca++-actin has been more widely studied in vitro, it would appear that actin in its physiological state is probably more polymerizable and more stable in the polymer form than previously considered.

Actins↗
PubMed1990

"Clamping" actin in polymerized form in electro-permeabilized neutrophils inhibits oxidase activation.

Electro-permeabilized neutrophils take-up small membrane-impermeant molecules into their cytoplasm, yet retain the ability to activate their oxidase and to transiently polymerize actin in response to f-met-leu-phe (fmlp). Using this system phalloidin was introduced into the cytosol in order to determine whether polymerization of actin affects oxidase activation. Cytosolic phalloidin prevented the depolymerization of actin following stimulation with fmlp, which was consequently "clamped" in the polymerized form during oxidase activation. Under these conditions oxidase activation was inhibited, the extent of inhibition being related to the level of polymerization at which the actin was "clamped". It was concluded that the actin polymerization which accompanies stimulation with fmlp interacts with other intracellular signals to limit oxidase activation.

Actin Cytoskeleton↗
PubMed1984

Polymeric complexes and fragments of albumin in normal human plasma.

Nitrocellulose blots of normal human plasma proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were examined for polymeric complexes and fragments of albumin using an immunoperoxidase-labelled mouse monoclonal anti-human albumin antibody. Under reducing conditions, no polymeric complexes were seen. Under non-reducing conditions, polymeric complexes were detected at the following molecular weights: 210 000, 168 000, 147 000, 132 000, and 110 000. These probably represent both homo- and heteropolymers of albumin. Fresh plasma samples were also analyzed by S-200 chromatography with the same results indicating that detection of polymeric complexes was not an artifact of the sodium dodecyl sulfate-polyacrylamide gel electrophoresis technique. In quantitative terms, polymeric complexes constituted 0.3-2.8% of the total albumin present. Fragments of albumin were also seen in normal human plasma with molecular weights of 45 000, 28 000 and 19 000. These fragments probably represent breakdown products of albumin in normal blood, and they constituted less than 2% of the total albumin present.

Antibodies, Monoclonal↗
PubMed1987

Does the degree of polymerization of haptoglobin influence the results of the radial immunodiffusion assay?

The degree of polymerization of haptoglobin (Hp) phenotypes 2-1 and 2-2 was studied. In individual samples the degree of polymerization tends to be positively correlated with the Hp concentration as determined by the radial immunodiffusion technique (RID), while an inverse relationship between the size of Hp polymers and the Hp concentration in RID was expected. After reductive cleavage of Hp, the apparent Hp concentration became higher in individual samples with different degrees of polymerization; the shift to higher values appeared to be independent of the degree of polymerization in samples of phenotypes Hp 2-1 and Hp 2-2. Consequently, the degree of polymerization as such does not have an impact on the outcome of RID at a technical level.

Electrophoresis, Polyacrylamide Gel↗
PubMed1994

Polymerization of actin from the thymosin beta 4 complex initiated by the addition of actin nuclei, nuclei stabilizing agents or myosin S1.

Thymosin beta 4 forms a 1:1 complex with actin and thereby prevents polymerization. Rapid formation of filaments from this complex was observed, however, when actin trimers were added. Polymerization can likewise be initiated by the addition of one equivalent of phalloidin or, less effectively, cytochalasin B. Since both toxins, which reportedly support nucleation, have similar effects as the covalently linked actin trimers, it appears that the formation of filaments from the actin-thymosin beta 4 complex depends on the availability of stable actin nuclei. Remarkably, rapid polymerization was also observed if small amounts of myosin S1 were added, suggesting that also myosin, a protein functionally connected with polymeric actin, can serve as a nucleation center. Considering the existence of thymosin beta 4 and related peptides in numerous mammalian tissues, our data suggest that spontaneous formation of microfilaments in non-muscle cells may be regulated at the level of nucleation. Uncontrolled polymerization induced by the formation of phalloidin-stabilized nuclei may explain the acute toxic effects of phalloidin in hepatocytes.

Actins↗
PubMed1996

Insulin and ATP stimulate actin polymerization in U937 cells by a wortmannin-sensitive mechanism.

ATP and insulin stimulate increases in phosphatidylinositol (3,4,5)-trisphosphate levels in myeloid-derived U937 cells. Quantification of FITC-phalloidin binding by fluorescence-activated cell sorting reveals that both ATP and insulin stimulate actin polymerization with distinctive kinetics in U937 cells. The response to ATP is rapid and dose-dependent with an EC50 of 200 nM, and is abolished by pre-incubation with the Ca2+ chelator BAPTA-AM. At 800 nM concentration, wortmannin, a potent inhibitor of phosphoinositide 3-kinase (PI3K), blocks the late, but not the early phase of actin polymerization stimulated by 100 nM ATP. Responses elicited by 10 micrograms/ml insulin are slower, smaller and more transient than responses to ATP, and are inhibited by preincubation with 100 nM wortmannin. Actin polymerization can also be stimulated by thapsigargin, but not by phorbol ester, providing further evidence for a role for Ca2+ in actin polymerization. These data implicate distinct Ca2+ and PI3K-mediated pathways in the regulation of actin polymerization.

Actins↗
PubMed1985

Kinetics of sickle hemoglobin polymerization. II. A double nucleation mechanism.

A double nucleation mechanism for the polymerization of sickle hemoglobin is described. The mechanism accounts for all of the major kinetic observations: the appearance of a delay, the high concentration dependence of the delay time, and the stochastic behavior of slowly polymerizing samples in small volumes. The mechanism postulates that there are two pathways for polymer formation: polymerization is initiated by homogeneous nucleation in the solution phase, followed by nucleation of additional polymers on the surface of existing ones. This second pathway is called heterogeneous nucleation. Since the surface of polymers is continuously increasing with time, heterogeneous nucleation provides a mechanism for the extreme autocatalysis that is manifested as an apparent delay in the kinetic progress curves. In this mechanism, each spherulitic domain of polymers is considered to be initiated by a single homogeneous nucleation event. The mechanism explains the irreproducibility of the delay time for single domain formation as arising from stochastic fluctuations in the time at which the homogeneous nucleus for the first polymer is formed. Integration of the linearized rate equations that describe this model results in a simple kinetic form: A[cosh(Bt)-1] (Bishop & Ferrone, 1984). In the accompanying paper (Ferrone et al., 1985) it was shown that the initial 10 to 15% of progress curves, with delay times varying from a few milliseconds to over 10(5) seconds, is well fit by this equation. In this paper, we present an approximate statistical thermodynamic treatment of the equilibrium nucleation processes that shows how the nucleus sizes and nucleation equilibrium constants depend on monomer concentration. The equilibrium model results in expressions for B and B2A as a function of monomer concentration in terms of five adjustable parameters: the bimolecular addition rate of a monomer to the growing aggregate, the fraction of polymerized monomers that serve as heterogeneous nucleation sites, the free energy of intermolecular bonding within the polymer, and two parameters that describe the free energy change as a function of size for the bonding of the heterogeneous nucleus to a polymer surface. This model provides an excellent fit to the data for B and B2A as a function of concentration using physically reasonable parameters. The model also correctly predicts the time regime in which stochastic behavior is observed for polymerization in small volumes.

Hemoglobin, Sickle↗
PubMed1991

Lithium increases actin polymerization rates by enhancing the nucleation step.

Lithium affects the polymerization mechanism of some cytoskeletal proteins in vitro, so its biological activity could also reflect lithium influence on assembly processes. Our data demonstrate that lithium nucleates actin polymerization and, in parallel, is less effective in the elongation step. Furthermore, falling-ball and fluorimetric tests suggested that lithium-induced actin polymers at steady-state are shorter than K(+)-polymerized actin filamentous structures. The lithium-induced actin assembly seems to follow the "reversible polymerization model" and the critical concentration of Li(+)-assembled actin at steady-state is markedly lower than that of sister actin samples polymerized by potassium chloride. Finally, the stabilization of actin nuclei induced by lithium ions could be related to their effect of lowering the dissociation rate constant.

Actin Cytoskeleton↗
PubMed1994

Acrylic resin-fiber composite--Part II: The effect of polymerization shrinkage of polymethyl methacrylate applied to fiber roving on transverse strength.

This study determined the effect of polymerization shrinkage of polymethyl methacrylate (PMMA) coating of fiber roving on the transverse strength of an acrylic resin-glass fiber composite. The test specimens were heat-cured acrylic resin reinforced with glass fibers. The glass fiber rovings were treated with four PMMA-MMA mixtures (30 specimens per group) of various ratios assumed to have different amounts of polymerization shrinkage. A transverse strength test was used to determine the fracture resistance of the test specimens and the polymerization shrinkage of the PMMA-MMA mixtures was measured. After the specimens were fractured, single glass fibers used to reinforce the test specimens were studied by SEM. The fracture resistance of the specimens was statistically different (p < 0.001) among treatments, and the polymerization shrinkage of the PMMA-MMA mixture also varied as the calculations predicted. The SEM micrographs showed differences in thickness of the acrylic resin layer on the surface of the fibers with PMMA-MMA mixtures of various ratios. According to the results, the ratio that caused only minor polymerization shrinkage of PMMA in the glass fiber roving improved the fracture resistance of the test specimens and seemed to increase the amount of PMMA inside the fiber roving.

Analysis of Variance↗