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PubMed1987

Polymerization shrinkage of methacrylate esters.

The polymerization shrinkage of a range of poly(n-alkyl methacrylates) in the range C1 to C16, some of their isomers and the polymers of cyclic and heterocyclic methacrylates have been measured using densitometry. The percentage volume shrinkage decreases with the size of the substituent side group. This proved to reflect the fact that the change in molar volume on polymerizing a methacrylate ester is reasonably constant at 22 cc/mol irrespective of the geometry of the substituent group. However, the glass transition temperature of the polymer depends very critically on the geometry of the side group. Hence one method for the development of low shrinkage glassy polymers is to investigate methacrylate esters of large molar volume, but with side group geometry that results in a high glass transition temperature. Polymerization shrinkage can be used to determine the degree of conversion of a polymer, using the value of 22 cc/mol as the change in molar volume.

Acrylates↗
PubMed1991

Low-frictional catheter materials by photo-induced graft polymerization.

To develop low-frictional catheters, photo-induced graft polymerization of N,N-dimethylacrylamide (DMAA) was performed on to films and tubes of ethylene-vinyl acetate copolymer (EVA) and poly(vinyl chloride) (PVC). Their surfaces became very slippery, when the materials were preirradiated with UV from a low-pressure mercury lamp, followed by graft polymerization with DMAA in the presence of small amount of riboflavin without degassing. Although no significant difference was observed in surface lubrication between the EVA film and the tube, the latter required an additional procedure for the graft polymerization, that is, removal of air trapped inside the tube. The surfaces of EVA and PVC tubes grafted with DMAA were found to exhibit frictional forces around 0.5 N against a PVC and a silicone surface under wet conditions, whereas the frictional force of the ungrafted tubes against the same substrates was 10 and 20 N for PVC and EVA, respectively.

Catheterization↗
PubMed1993

Synergistic inhibition of the calcification of glutaraldehyde pretreated bovine pericardium in a rat subdermal model by FeCl3 and ethanehydroxydiphosphonate: preincubation and polymeric controlled release studies.

Calcification is a frequent cause of the clinical failure of bioprosthetic heart valves fabricated from glutaraldehyde-pretreated porcine aortic valves or glutaraldehyde-pretreated bovine pericardium (GPBP). We investigated the hypothesis that ferric chloride (FeCl3) and sodium-ethanehydroxydiphosphonate (EHDP) may act synergistically to prevent bioprosthetic tissue calcification. Pre-incubations and controlled release systems were studied individually. FeCl3-EHDP polymeric controlled release matrices were formulated using silicone rubber and evaluated for in vitro release kinetics at pH 7.4 and 37 degrees C. The effects of Fe-EHDP synergism on GPBP calcification were investigated with 21 d subdermal implants in 3 wk-old male rats. Results demonstrated that levels of Fe3+ and EHDP uptake, measured in GPBP tissues pre-incubated first in an FeCl3 solution (10(-5) M) followed by an EHDP solution (0.1 M), were higher than in the reverse order of incubation. In the first series of rat implants, GPBP was pre-incubated in either FeCl3 or Na2EHDP solutions, or sequential pre-incubations of first FeCl3 and then Na2EHDP solutions, or the reverse. The inhibition of calcification was greatest when FeCl3 (first pre-incubation, 10(-5) M) was combined with Na2EHDP (second pre-incubation, 0.1 M) (1.78 +/- 0.2 micrograms of Ca2+/mg of dried tissue) compared with the other pre-incubation groups: EHDP (first pre-incubation) combined with FeCl3 (second pre-incubation) (21.7 +/- 6.4), FeCl3 solution alone at 10(-5) M (27.9 +/- 10.7), Na2EHDP solution alone at 0.1 M (52.3 +/- 11.9) and the control group (72.3 +/- 10.2). In a second series of implants, GPBP specimens were co-implanted with individual controlled release systems containing one of the following formulations (weight percentage in silicone rubber): 1% FeCl3, 20% CaEHDP, 20% protamine sulphate, 1% FeCl3-20% CaEHDP, and 1% FeCl3-20% protamine sulphate. The 1% FeCl3-20% CaEHDP silicone-rubber matrices were the most effective for inhibiting GPBP mineralization (13.7 +/- 3.0 micrograms Ca2+/mg of dried tissue) compared with non-drug silicone co-implant controls (74.7 +/- 5.58 micrograms Ca2+/mg of dried tissue) and other polymeric treatment groups (32.3 +/- 2.3-80.0 +/- 19.7). No adverse effects on bone or overall growth of any treatment protocols were noted. Thus, combinations of FeCl3 and EHDP, using either pre-incubations or polymeric controlled release, were synergistic for inhibiting GPBP calcification.

Animals↗
PubMed1994

Studies on a new radiopaque polymeric biomaterial.

A new radiopaque polymeric biomaterial has been synthesized. The material, which actually represents an entire family of analogous radiopaque materials, is composed of 2-(p-iodobenzoyl)-ethyl methacrylate (compound 1, 21 mol%), methyl methacrylate (MMA, 60 mol%), and 2-hydroxyethyl methacrylate (HEMA, 19 mol%). The terpolymer was synthesized in a radical polymerization reaction at elevated temperature in N,N-dimethylformamide (DMF). The product was subjected to a set of physicochemical characterization techniques (gel permeation chromatography, 500 MHz 1H NMR in deuterated dimethylsulphoxide (d6-DMSO) solution, differential scanning calorimetry, dynamic water contact angle measurements), as well as to an in vitro thrombogenicity assay. Furthermore, scanning electron microscopy was used to study interactions of the material with blood platelets. The most important findings are: (a) the material is a genuine polymer with excellent X-ray visibility, even in the form of thin (0.4 mm) drawn fibres. This was established under realistic conditions. (b) The material exhibits low in vitro thrombogenicity, i.e. comparable to polyvinyl chloride, which is known as a passive material. These observations lead us to the suggestion that this type of radiopaque polymer holds promise with respect to application as a construction material for a new type of endovascular stent. This could be relevant in particular to stents to be used in conjunction with percutaneous transluminal coronary angioplasty (PTCA), also known as Dottering. Currently there is a clear trend away from metallic stents towards all-polymeric stents, since the latter have superior biocompatibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatible Materials↗
PubMed1991

Quantitative fluorescence techniques for the determination of local microtubule polymerization equilibria in cultured neurons.

The local control of intracellular microtubule polymerization equilibria has been hypothesized to be an important factor in the determination of neurite extension and other examples of cellular asymmetry. Provided that the quantum yield of the fluorophore remains constant, the combination of fluorescent analogue cytochemistry, differential extraction protocols, and quantitative video microscopy makes it possible to measure local fractions of cytoskeletal protein in polymer, even when it is impossible to resolve individual fibrils of the polymer. We have developed appropriate quantitative video microscopic techniques for measuring the fluorescence of a fluorescent analogue-injected neurite before and after extraction under microtubule-stabilizing conditions. We have used these methods to demonstrate that tetramethylrhodamine-n-hydroxysuccinimide tubulin is an appropriate fluorescent analogue, allowing us to measure fractions of tubulin in polymer locally within PC12 neurites. As would be expected, the fraction of tubulin fluorescent analogue in polymer approaches 1.0 in neurites exposed to the microtubule-stabilizing drug taxol and is close to 0 in neurites injected and extracted in the cold, or extracted under microtubule-destabilizing conditions. We have, therefore, developed a tool that allows us to measure microtubule polymerization equilibria out the neurites of cells in culture, which will allow us to test hypotheses that factors which affect neurite outgrowth do so by means of effects on microtubule polymerization equilibria.

Adrenal Gland Neoplasms↗
PubMed1994

Synthetic polymeric inhibitors of influenza virus receptor-binding activity suppress virus replication.

A new approach to anti-influenza chemotherapy is based on the development of synthetic inhibitors of virus attachment to host cells. These inhibitors are prepared by anchoring the minimum receptor determinant of influenza virus, sialic acid, to polymeric or liposomal carriers. In this study, a series of poly(acrylic acid-co-acrylamides) and dextrans bearing pendant glycylamidobenzylsialoside groups were synthesized and evaluated for their binding to a panel of influenza A and B virus strains and for their ability to inhibit virus infectivity in cell culture. Significant type-, subtype-, and strain-specific variation in virus susceptibility to the synthetic inhibitors was observed. Among the viruses tested, H3 subtype strains evolved in humans since 1975 were the most sensitive, while the earlier H3 viruses and the type B strains were resistant. The virus-inhibitory potency of the polymeric sialosides correlated with their bindings to the virus, and was dependent on the virus affinity for the ligand, the density of the ligand, and the nature and molecular mass of the polymeric carrier. In embryonated eggs, the antiviral effect of poly(acryloyl-glycylamidobenzylsialoside-co-acrylic acid) was comparable to that of equine alpha 2-macroglobulin.

Antiviral Agents↗
PubMed1988

Inhibition of DNA polymerization and DNA transcription to RNA by seminal plasma peptides.

An oligopeptide fraction purified from the extracellular compartment of bull semen and strongly interacting with DNA was shown to hinder mononucleotide polymerizations to DNA and RNA in vitro. The fraction, collectively called seminal plasma inhibitor, was active in the endogenous DNA and RNA polymerase reactions of the nuclei from rat hepatocytes and in the analogous nucleotide polymerizations catalyzed by purified enzymes of bacterial origin. The type of the induced inhibition was studied using the RNA polymerase from Escherichia coli as a representative nucleotidyl transferase. In the enzymatic polycondensation of mononucleotides, the seminal plasma inhibitor appeared to exert its effect mainly by a competitive inhibition for the utilization of DNA templates without specificity with respect to the source and the base sequence of DNA. Concavities of the plots of V0/Vi versus the amounts of inhibitor in the nucleotide polymerizing reactions and of the Dixon plots in the assays of RNA polymerase from E. coli suggested that the isolated oligopeptide fraction contained more than one active molecular species with differential effects at low and high doses. Preliminary results on the microheterogeneity of the seminal plasma inhibitor supported this contention.

Amino Acids↗
PubMed1982

Nucleation of actin polymerization from profilactin. Opposite effects of different nuclei.

The lag in polymerization of calf spleen profilactin in response to addition of MgCl2 can be overcome by small amounts of spectrin-actin-band 4.1 complex, covalently crosslinked actin oligomers or sonicated F-actin. All of these factors also nucleate polymerization of pure actin. Another nucleator of actin polymerization, villin, delays filaments formation from profilactin. A simple model of the interaction of profilin with actin can explain these apparently conflicting results in terms of the polarity with which actin filaments elongate from the different nuclei.

Actins↗
PubMed1987

Tropomyosin from human erythrocyte membrane polymerizes poorly but binds F-actin effectively in the presence and absence of spectrin.

Actin in the human erythrocyte forms short protofilaments which are only long enough to accommodate tropomyosin monomers (Shen, B.W., Josephs, R. and Steck, T.L. (1986) J. Cell Biol. 102, 997-1006). This interaction between actin and tropomyosin monomers is predicted to be weak, since tropomyosin polymerization parallels its affinity for F-actin. We examine the binding of human erythrocyte tropomyosin to actin in the presence and absence of spectrin and its ability to polymerize. The binding of human erythrocyte tropomyosin to F-actin is not affected appreciably by the present of spectrin. Saturating F-actin with erythrocyte tropomyosin, however, weakens the binding of spectrin dimers to actin. Although tropomyosin from human erythrocyte and rabbit cardiac muscle have similar affinity for F-actin, the polymerizability of erythrocyte tropomyosin as determined by viscosity measurements is much reduced relative to muscle tropomyosin. This unusual property of erythrocyte tropomyosin is likely due to differences in its primary structure from other known tropomyosin at the amino and carboxyl terminal regions which are responsible for its head-to-tail polymerization and cooperative binding to F-actin. Analysis of the distribution of tyrosine by 2-dimensional tryptic mapping of 125I-labelled erythrocyte tropomyosin shows that tyrosine at positions 162, 214, 221, 261 and 267 in rabbit cardiac tropomyosin are conserved in human erythrocyte tropomyosin but Tyr-60 is absent. This observation suggests that erythrocyte tropomyosin has a carboxyl terminal region similar to its muscle counterparts but its amino terminal region resembles that of platelet tropomyosin which also lacks Tyr-60.

Actins↗
PubMed1987

Fibrinogen and the early stages of polymerization to fibrin as studied by dynamic laser light scattering.

Human fibrinogen and the polymerization of fibrin after activation by the enzymes, thrombin and Batroxobin, were studied by means of dynamic laser light scattering (DLS). The apparent diffusion constant, D, for fibrinogen was measured and has a value of (1.80 +/- 0.42) X 10(-7) cm2 X s-1. D was found to contain contributions from the translational diffusion constant (Dt) as well as from the rotational diffusion constant (Dr). A comparison between experimental and calculated values of Dr and Dt suggests that fibrinogen in the absence of added Ca2+ expresses a certain degree of flexibility, while it is straightened in the presence of added Ca2+. The time dependence of D showed periodic oscillations, while the average D values decreased with time. Thrombin and Batroxobin caused similar behaviour of D. The period length was related to the enzyme concentration, clotting time (Ct) and the rate of release of fibrinopeptide A (FPA). No periodic oscillations were observed in experiments where the enzyme was replaced by saline, or in experiments using a dysfunctional fibrinogen (fibrinogen Aarhus) which displayed slow rates of FPA-release and polymerization. We propose that the periodic oscillations in a system far from equilibrium may be explained by conformational changes occurring in the fibrinogen molecule during enzyme activation and polymerization.

Batroxobin↗
PubMed1987

Influence of phalloidin on both the nucleation and the elongation phase of actin polymerization.

Phalloidin, a heptapeptide from the mushroom Amanita phalloides, increased the velocity of actin polymerization, but slightly decreased the velocity of elongation (polymerization onto sonicated F-actin). A plot of log polymerization velocity vs. log actin concentration was less steep in the presence of phalloidin than in its absence, suggesting that the filament nucleus is smaller in the presence of phalloidin than in its absence.

Actins↗
PubMed1987

Influence of phalloidin on ATP hydrolysis during actin polymerization.

The influence of phalloidin on the ATP hydrolysis associated with actin polymerization was investigated. Whereas in the absence of phalloidin actin-bound ATP was totally hydrolyzed during polymerization, ATP hydrolysis was not complete after actin polymerization in the presence of phalloidin: 5-10% of ATP remained unhydrolyzed and disappeared only after 2 days.

Actins↗
PubMed1994

Polymerization of actin induced by actin-binding fragments of caldesmon.

Our earlier studies revealed that caldesmon causes assembly of G-actin into polymers morphologically indistinguishable from those formed in the presence of salt (Gałazkiewicz, B., Belagyi, J. and Dabrowska, R. (1989) Eur. J. Biochem. 181, 607-614). In this work we have investigated the effect of actin-binding fragments of caldesmon on actin polymerization process followed by measurements of the changes in fluorescence of pyrenyl conjugated with G-actin and ATP hydrolysis. The results indicate that C-terminal 34 kDa fragment of caldesmon containing two actin-binding sites and 19 kDa containing high-affinity binding site have similar capability to polymerize actin to that of intact molecule. Binding of each of these fragments to G-actin causes bypassing of nucleation phase. The 11.5 kDa fragment comprising low affinity actin-binding site has much lower potency to polymerize actin. Conformation of actin monomers in filaments formed upon 19 kDa fragment and that formed upon 11.5 kDa fragment differs. The former fragment seems to resemble more conformation of monomers in filaments formed upon intact caldesmon than the latter one.

Actins↗
PubMed1994

Mechanism of ATP hydrolysis by polymeric actin.

The lag between polymerization of actin and ATP hydrolysis in actin filaments was analyzed in terms of the mechanism of the hydrolysis reaction. Under the experimental conditions (100 mM KCl and 1 mM MgCl2, or without KCl, 1 mM MgCl2 and 0.4 mM EGTA, 25 degrees C) ATP hydrolysis lagged behind polymerization by about 100 s independently of the concentration of polymerizing filament ends and of the actin monomer concentration. Three models of ATP hydrolysis were compared to experimental data: (i) Random ATP hydrolysis, ATP is assumed to be hydrolyzed at a rate that is independent of the type of the nucleotide bound to adjacent filament subunits. (ii) Cooperative hydrolysis, the rate of ATP hydrolysis is thought to depend on the type of nucleotide bound to adjacent subunits. (iii) Sequential hydrolysis, ATP is assumed to be hydrolyzed only at the interface between ATP-subunits and ADP-subunits. The model of sequential ATP hydrolysis could be excluded. The results were in agreement with random or cooperative ATP hydrolysis. The differences of the rates of ATP hydrolysis by a random or cooperative mechanism are so small that based on the experimental results no distinction between these two mechanisms could be made. All available evidence points towards a mechanism of ATP hydrolysis in which several or perhaps many interfaces between ATP- and ADP-subunits are formed within a filament.

Actins↗
PubMed1994

Mechanism of S100 protein-dependent inhibition of glial fibrillary acidic protein (GFAP) polymerization.

S100 protein, a subfamily of Ca(2+)-binding proteins of the EF-hand type, was recently shown to bind to and to inhibit the polymerization of the glial fibrillary acidic protein (GFAP), the intermediate filament component of astroglial cells, in the presence of micromolar levels of Ca2+ (J. Biol. Chem. 268, 12669-12674). By a sedimentation assay and viscometry we show here that S100 protein interferes with the very early steps of GFAP polymerization (nucleation) and with the GFAP polymer growth, thereby retarding the onset of GFAP assembly, reducing the rate and the extent of GFAP assembly, and increasing the critical concentration of GFAP assembly. Moreover, S100 protein disassembles preformed glial filaments. All the above effects can be explained by sequestration of soluble GFAP by S100 protein, as also indicated by the stoichiometry of S100 protein binding to GFAP and of S100 protein effects on GFAP assembly. Our data suggest that S100 protein might serve the function of avoiding excess GFAP polymerization and might participate in remodeling of glial filaments following elevation of the intracellular free Ca2+ concentration. Also, our data lend support to the notion that intermediate filaments are dynamic cytoskeleton structures that assemble and disassemble, and to the existence of cytoplasmic factors implicated in the regulation of the state of assembly of intermediate filaments.

Animals↗
PubMed1993

Ultra-high strength, self-reinforced absorbable polymeric composites for applications in different disciplines of surgery.

Biodegradable (or absorbable), self-reinforced polymeric composites have potential applications as temporary fixation materials in the treatment of damaged or operated tissues. These materials have high strength and appropriate stiffness and strength retention which can be tailored according to the healing rate of recovering tissues. Macroscopical, absorbable, ultra-high strength, self-reinforced, polymeric composites can be manufactured by creating the polymeric microstructure, where oriented reinforcing elements and matrix material, which have the same chemical element composition, are combined with each other. Self-reinforced materials can be processed into the form of rods, screws, tacks, cerclages, clamps, plates, spirals, etc. Such implants have attractive application possibilities in different disciplines of surgery, such as orthopaedics and traumatology, in maxillofacial, oral and dental surgery and in internal organ surgery.

Animals↗
PubMedDate not supplied

Enzymatic polymerization of 5-mercuriuridine-5'-diphosphate with polynucleotide phosphorylase from E. coli.

We report the polymerization of 5-mercuriuridine-5'-diphosphate (ppUHgX), in the presence of an excess of beta-mercaptoethanol, with polynucleotide phosphorylase from E. coli. A degradation of mercurated nucleotides with mercaptans was observed and about 30% of incorporation of mercury in the polymer was obtained after treatment with pancreatic RNase. The influence of ppUHgX and pUHgX with or without beta-mercaptoethanol was also studied on the polymerization of UDP. The ppUHgX did not polymerize in the absence of beta-mercaptoethanol.

Chromatography, Thin Layer↗
PubMedDate not supplied

On the polymerization state of recA in the absence of DNA.

We present an electron microscopy study on the polymerization state of recA in the absence of DNA. In solution recA exists as monomers, small complexes not clearly longer than wide (approximately 9-18 nm), and filaments (diameter approximately 11 nm and variable lengths). We have attempted to quantify the relative amounts of these species by length measurements of the particles on electron micrographs. The percentages of each of these types was found to depend on recA concentration, temperature and presence in the incubation mixture of Mg2+, ATP gamma S, salt or D2O. These additives do not have an absolute effect on polymerization but rather shift the polymerization equilibrium of recA (which depends on recA concentration) up or down the concentration scale.

Adenosine Triphosphate↗