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 1,405 records · Page 78Linked to original sources
PubMed1983

Immune complexes in IgA nephropathy: presence of antibodies against diet antigens and delayed clearance of specific polymeric IgA immune complexes.

Several features suggest that IgA nephropathy is an immune complex (IC)-mediated disease. The source of antigen(s) is unknown but the predominant involvement of IgA suggest that it is associated in some way with the gut or respiratory tract. Taking into account the specific hepatobiliary transport by polymeric IgA of circulating antigens entering through the mucosal surfaces we examined the possible involvement of antibodies against food antigens in the circulating IC and the existence of a defect in their blood clearance in patients with IgA nephropathy. A rise in multimeric IgA-IC (Raji assay) occurred in three of seven control subjects with a peak at 2-4 h after food ingestion. The amount of multimeric IgA-IC present at fasting in four out of six patients, diminished 2-4 h after food challenge, reaching a new peak around 6 h. At fasting, three out of six patients had IC containing antibodies against diet antigens (e.g. ovalbumin). These IC paralleled, both in patients and controls, the levels of multimeric IgA-IC. In patients small multimeric IgA-IC predominated at fasting and 24 h after food ingestion, while larger IC were detected at 2-4 h of food challenge. The specific polymeric IgA-IC showed in controls a maximal peak with similar distribution to that of multimeric IgA-IC, but with a quicker disappearance from the circulation. By contrast, polymeric IgA-IC remained elevated 24 h after food ingestion in most patients. These results suggest that antibodies against common antigens are within circulating IC and that a defect in the hepatic clearance of circulating polymeric IgA-IC exists in patients with IgA nephropathy.

Antibodies↗
PubMed1984

[Effects of pH and ATP on the cytoplasm of Amoeba proteus: relation between cytoplasm motility and actin polymerization].

The effect of pH and ATP was studied on isolated cytoplasm of Amoeba proteus. These two parameters were shown to influence both the motility and the organization of actin filaments in the isolated cytoplasm. Furthermore, our results demonstrate that there is a relationship between the motility and the polymeric state of actin. When the isolated cytoplasm is non-motile, actin is highly polymerized into long filaments arranged parallel in bundles. When this cytoplasm is motile, however, actin can either be weakly polymerized, i.e. observed as few short filaments, or can be polymerized in long branched filaments forming a loose network.

Actins↗
PubMed1984

Rate constants for actin polymerization in ATP determined using cross-linked actin trimers as nuclei.

Chemically cross-linked actin trimer, prepared from F-actin covalently cross-linked by N-N'-p-phenylenebismaleimide, was used to nucleate the assembly of actin polymers under a variety of ionic conditions at 25 degrees C. Gel-filtered G-actin (5% labeled with N-pyrenyl iodoacetamide) was prepared in buffers containing 5 mM Tris X HCl, 0.2 mM ATP, 0.05 mM MgCl2 or 0.1 mM CaCl2, 0.2 mM dithiothreitol, and 0.01% sodium azide, pH 7.5. Polymerization was initiated by adding salt to a solution of actin monomer (2-25 microM) mixed with actin trimer (0-24 nM). Pseudo-first-order polymerization kinetics were observed in all cases following a lag phase of 30-75 s. The length of the lag phase was independent of trimer concentration, monomer concentration, or preincubation of monomer or trimer in polymerizing buffer. A simple model is presented which explains all of the observed features of the lag phase. Lower limits for the sums of the elongation rate constants at the two filament ends, calculated assuming each trimer acts as a seed, were in the range 1.4-5.2 microM-1 s-1, and lower limits for the polymer dissociation rate constants (calculated from the elongation rate constants and the critical actin concentration) were 0.4-1.9 s-1, depending on ionic conditions. The observed rate constants were independent of actin concentration or trimer concentration under a given ionic condition. These polymerization rate constants are in good agreement with the values others have obtained by measuring the growth of actin filaments by electron microscopy.

Actins↗
PubMed1982

Medical applications of polymeric materials.

This review presents a critical analysis of the use of polymeric materials in medicine, other than orthopedic and dental applications. Primary focus is on problem areas with various polymers and plastics in disposable products, implants, and devices, including artificial heart valves, cardiovascular prostheses, cardiopulmonary bypass, and hemodialysis. Several problems are presented especially in the biological evaluation of polymeric materials and devices, including species-related hematological differences and the role of the complement system in blood compatibility. Finally, examples of newer medical applications of polymeric materials are discussed, such as controlled drug delivery, polymeric drugs, and artificial skin.

Biocompatible Materials↗
PubMed1982

Changes in actin lysine reactivities during polymerization detected using a competitive labeling method.

We have studied the structure of actin by measuring the relative reactivities of lysines with acetic anhydride using a competitive labeling procedure comparing monomeric globular actin. monomeric actin in the presence of salt, and filamentous actin polymerized in 100 mM NaCl and 100 mM NaCl, 2 mM MgCl2. We have identified 12 of the 19 lysines: 18, 50, 61, 68, 113, 191, 237, 290, 315, 325, 327, and 358. In all conditions, Lys (325, 327) is the most reactive. In globular actin, Lys 18, 191, 290, 314. and 358 are less than 20% as reactive as Lys (325, 327); the remaining have intermediate reactivities. On polymerization in the presence of NaCl and Mg2+, lysines 50, 61, 68, 113, and 290 become less reactive relative to Lys (325, 327). The changes in Lys 50, 61, and 113 are due largely to the polymerization event whereas those in Lys 68 and 290 appear to be an effect of Mg2+. Lys 18, 191, and 358 increase in relative reactivity when cation is added to the monomer and then become less reactive in the polymer, showing no large overall change in reactivity relative to the monomer in the absence of salt. Lysines that are reduced in reactivity upon polymerization indicate possible contact regions between actin monomers in the filament in the NH2-terminal third of the protein.

Acetic Anhydrides↗
PubMed1983

[Mechanism of the formation of complexes between monomer fibrin and the inhibitor of its polymerization - fragment D].

It was found that fragment D derived from fibrinogen may be coupled with the fibrin monomer to produce complexes of unstable and stable types. The native fibrin monomer forms unstable complexes; the stable ones arise when the labile peripheral domains of the fibrin molecules are reversibly modified and their specific intermolecular affinity for the thrombin-activated central domains is lowered or eliminated. Fragment D, the free peripheral domain possessing polymerization centers, is strongly bound to the modified monomer occupying the polymerization sites of its central domain. The modification was induced by using acid pH (around 3.7) or by urea or NaBr taken at concentrations which caused no denaturation. In neutral media the acid-modified monomer passes to its normal state which is accompanied by simultaneous decrease of fragment D binding and restoration of codgulability. Fragment D presumably competes with the peripheral domain for the central one. Peripheral domains of the intact monomer are predominant competitors; fragment D only reduces the rate of polymerization due to temporary complex formation. However, modification results in a formation of stable complexes and thus decreases the accumulation of polymeric fibrin.

Animals↗
PubMed1981

The membrane receptor for polymeric immunoglobulin is structurally related to secretory component. Isolation and characterization of membrane secretory component from rabbit liver and mammary gland.

The membrane receptor of epithelial cells which binds polymeric immunoglobulins and mediates their transepithelial translocation is antigenically related to secretory component (SC), a glycoprotein produced by the epithelial cells. In rabbit milk, secreted SC is found either bound to polymeric immunoglobulin A (IgA) or in a free form. It is comprised of a heterogeneous population of molecules with apparent Mr = 83,000 and 80,000 (upper doublet) and 58,000 and 55,000 (lower doublet). Membrane SC was isolated by immunoadsorption from deoxycholate-solubilized plasma membranes of rabbit liver and mammary gland. The purified proteins, heterogenous in size with apparent Mr = 120,000 and 116,000 (upper doublet) and 95,000 and 91,000 (lower doublet), were amphiphilic. One-dimensional peptide maps revealed extensive structural homology between both the upper doublets of the membrane and secreted SC, as well as between the lower doublets. This indicates that the high Mr membrane SC of hepatocytes and mammary cells are precursors of the lower Mr secreted SC found in bile and milk. All four membrane SC, purified in high yield from rabbit liver by immunoadsorption and preparative electrophoresis in the presence of sodium dodecyl sulfate, bound IgA dimer specifically. The affinity (Kd approximately equal to 10 nM) was similar to the one observed in free SC-IgA dimer interaction. Only the membrane proteins recognized by the anti-SC antibodies were able to bind polymeric IgA. In liver membrane preparations, the receptor was localized at the surface of smooth vesicles, using IgA dimer-biotin and avidin-gold. Our results indicate that the high Mr membrane SC is the plasma membrane receptor for polymeric immunoglobulin.

Animals↗
PubMedDate not supplied

The influence of polymerization conditions on the 3-ketosteroid delta 1-dehydrogenase activity of Mycobacterium globiforme cells included in a gel.

The influence of the conditions of polymerization and the structure of the polyacrylamide gel (PAG) on the 3-ketosteroid delta 1-dehydrogenase activity of a culture of M. globiforme 193 was studied. A clear dependence of the enzymatic activity on the temperature regime and the duration of the polymerization process was established. The reason for the fall in activity with a rise in temperature and an increase in the duration of the polymerization process is the diminution of the quantity of viable cells. The death of the cells is caused by the action of the monomers. The maximum 3-ketosteroid delta 1-dehydrogenase activity appears when the immobilized cells are maintained in a viable state, accomplished by adopting a short time of polymerization (1--2 min) at a temperature of 4--12 degrees C. The specific activity of free cells of M. globiforme and cells immobilized under these conditions is 0.15 mumoles/mg cells . min. The reason for the low activity in a 20% gel is apparently the limited rate of diffusion of the substrate into the gel, conditioned by the small dimensions of the pores of the gel. A change in the concentration of N,N'-methylene bisacrylamide (MBA) from 0.25 to 2% in 5 and 10% gels does no affect the rate of delta 1-dehydrogenation of the substrate.

Chemical Phenomena↗
PubMed1980

Microtubule-associated proteins from cultured HeLa cells. Analysis of molecular properties and effects on microtubule polymerization.

We have attempted a biochemical characterization of the microtubule-associated proteins (MAPs) of cultured HeLa cells. The HeLa MAPs consist of a group of three polypeptides of 200,000 to 220,000 molecular weight (the 210K MAP) and a protein of 125,000 molecular weight (the 125K MAP). The solution properties of the HeLa MAPs were examined using molecular sieve chromatography and sucrose gradient sedimentation. With both analytical procedures, the 125K and 210K MAPs behaved independently of one another. The effects of each of the MAPs on microtubule polymerization were also studied. Both the 125K and 210K MAPs stimulated the polymerization of pure tubulin. The effect of high levels of MAPs on microtubule polymerization was also examined. Increasing the concentration of MAPs at a constant tubulin concentration increased both the rate and extent of microtubule polymerization. The 125K and 210K MAPs showed independent behavior with respect to binding to microtubules. The 210K MAP saturated its binding sites at a level of 14.0% (210K MAP:tubulin in polymer, w/w), while the 125K MAP showed no saturation even at a level of 18.3%. These results demonstrate that the 125K and 210K MAPs are distinct molecular species, differing in their solution properties and their binding to microtubules. The 210K MAP showed some similarities and some differences when compared to the porcine brain high molecular weight MAP. The HeLa MAPs, although showing some properties similar to brain MAPs, are nevertheless distinctive in several respects and may best be considered as separate though possibly related species.

Centrifugation, Density Gradient↗
PubMed1994

Alternative modes of polymerization distinguish the subunits of equine infectious anemia virus reverse transcriptase.

A comparative study of recombinant 51- and 66-kDa subunits comprising equine infectious anemia virus reverse transcriptase (EIAV RT) is reported. Both polypeptides sedimented as stable homodimers (molecular mass, 102 and 132 kDa, respectively) when analyzed by rate sedimentation through glycerol gradients. Consistent with their dimer composition, each preparation displayed considerable levels of both RNA- and DNA-dependent DNA polymerase activity on different homopolymeric template/primer combinations. However, a detailed analysis of the polymerization products indicated qualitative differences. Whereas p66 EIAV RT proceeded essentially unimpaired along both RNA and DNA templates, p51-catalyzed DNA synthesis was interrupted close to or in the immediate vicinity of the primer. A series of "programmed" 2-step polymerization reactions suggests that p51 EIAV RT enters an abortive mode of polymerization. Duplication of this observation with p51 human immunodeficiency virus-1 RT, together with recent observations from murine RT, suggests that lack of a ribonuclease H domain and loss of contact with the nascent product from the polymerase active center have profound consequences on the mode of polymerization.

Base Sequence↗
PubMed1995

Chronic myeloid leukemia granulocytes exhibit reduced actin polymerization after chemotactic peptide stimulation.

Polymorphonuclear leukocytes (PMNL) from chronic myeloid leukemia (CML) patients are defective for chemotaxis in response to the synthetic chemotactic peptide n-formyl-methionyl-leucyl-phenylalanine (fMLP) as compared to normal PMNL. The present study investigated whether the defective chemotactic response was mediated through altered actin polymerization induced with fMLP. Granulocytes isolated from seven normal subjects and seven CML patients were stimulated with fMLP and lysed with Triton containing buffer at time points of 0, 30 seconds, and 1, 2, and 10 minutes. The Triton insoluble cytoskeleton containing polymerized actin was analyzed by SDS-PAGE and densitometry. The CML PMNL polymerized significantly lesser actin than normal PMNL on stimulation with 10 nM (p > 0.05) and 1 nM (p > 0.01) fMLP. This lower actin polymerization observed in fMLP-stimulated CML PMNL may be responsible for the defective chemotaxis seen in these cells.

Actins↗
PubMed1995

[Experimental studies of the risks of endocapsular polymerization of injectable intraocular lenses].

Various experimental lens refilling procedures have been proposed. One of these methods uses endocapsular polymerization of the injected material by light exposure. In this study we wanted to characterize the potential risks of this procedure due to light and temperature hazards. We performed in vitro experiments on enucleated pig eyes and an in vivo study on 15 rabbits. During the polymerization process the highest temperature recorded (45.1 degrees C) was measured at the posterior lens capsule for a few seconds. The measured irradiance (0.065 W/cm2) and the risk of photochemical damage to the retina during 20 s of polymerization was comparable to that caused by 1.5 min of standard coaxial illumination with our operating microscope. In vivo we found no serious inflammatory reactions except for four cases where surgical problems had occurred. No direct retinal damage could be detected histopathologically. In conclusion, we think that lens refilling and endocapsular polymerization are promising techniques. However, refilling materials with better physical properties than those available so far need to be developed.

Acrylates↗
PubMed1976

On the processive mechanism of Escherichia coli DNA polymerase I. Delayed initiation of polymerization.

Escherichia coli DNA polymerase I shows a delay in the initiation of polymerization after binding to the cohesive ends of lambda DNA. This delay is significantly longer than the time required for the synthesis of an octanucleotide sequence on the right-hand cohesive end of the lambda DNA. When the extent of polymerization is limited by omission of one or more of the deoxynucleoside triphosphates, and polymerization started again by their addition, the delay still occurs. A plausible explanation for this phenomenon is that two forms of the enzyme or enzyme - DNA complex exist, only one of which is active. The delay, therefore, represents the time necessary to convert the inactive to the active form of the enzyme or enzyme complex. One consequence of the defect in DNA polymerase I, due to the polA12 mutation, is apparently to alter the equilibrium between the two forms. However, the rate of polymerization and the rate of conversion of inactive to active enzyme or enzyme complex are not changed significantly.

Coliphages↗
PubMed1994

Actobindin induces the accumulation of actin dimers that neither nucleate polymerization nor self-associate.

Actobindin purified from Acanthamoeba castellanii inhibits the nucleation, but not the elongation, phase of actin polymerization. Previously, we had speculated that actobindin, which can simultaneously bind two actin monomers (Bubb, M.R., Lewis, M.S., and Korn, E.D. (1991) J. Biol. Chem. 266, 3820-3826), might preferentially interact with small oligomers and inhibit their ability to elongate (Lambooy, P.K., and Korn, E.D. (1988) J. Biol. Chem. 263, 12836-12843). In the accompanying paper (Bubb, M.R., Lewis, M.S., and Korn, E.D. (1994) J. Biol. Chem. 269, 25587-25591), we show that under non-polymerizing conditions, actobindin binds to covalently cross-linked actin dimers with higher affinity than to two actin monomers. The sedimentation velocity and fluorescence anisotropy experiments described in this paper show that actobindin prevents the formation of actin oligomers larger than an actin dimer under conditions in which, in the absence of actobindin, actin rapidly polymerizes to F-actin with no detectable small oligomers. Moreover, the molar concentration of actin dimer formed in the presence of actobindin can exceed the total actobindin concentration. These results indicate that actobindin does not form a stable complex with native actin dimer but, rather, causes the accumulation of dimers that are unable to nucleate polymerization or self-associate.

Acanthamoeba↗
PubMed1994

Relationship between degree of polymerization of resin composite and bond strength to Gluma-treated dentin.

The purpose of the present study was to investigate the relationship between shear bond strength (SBS) to dentin and degree of polymerization of resin adjacent to the coupling interface. A hybrid-type resin composite was polymerized on Gluma-treated dentin at thicknesses of 1, 2, 3 and 5 mm, respectively, with seven different light activation times (LAT) from 3 through 180 seconds. SBS of the specimens was determined 10 minutes after the end of light activation. The degree of polymerization of resin close to the dentin interface was determined by Wallace Indentation Depth (WID) of specimens polymerized under the same conditions as the SBS samples, however, separated from the dentin surface by a thin glass plate. Consistent relationships were found for SBS vs. LAT and WID vs. LAT by regression analyses (y = A+B/x). There was a strong linear correlation between SBS and WID (r = -0.93), indicating that the early bond strength to Gluma-treated dentin is a function of mechanical characteristics of resin close to the bonding interface.

Composite Resins↗
PubMedDate not supplied

A predictive model for the polymerization of photo-activated resin composites.

This study investigated the relative significance of irradiation duration (20, 40, 60, or 80 seconds) and intensity; filler type (Silux Plus, a microfill or P-50, a hybrid); and shade (Universal or Gray) on the polymerization of resin composite within the depth of a simulated photopolymerized restoration. From the data, a mathematical model that predicts the extent of resin polymerization based upon the above stated variables was generated. The monomer conversion of specimens was determined by infrared spectroscopy. The results are of great clinical use and indicate that the most significant factor influencing resin composite polymerization is thickness of overlying resin composite. Both duration of exposure and light intensity demonstrate high and equal impact. Color and filler type have only minimal influence. The predictive model for resin composite polymerization provided a very good fit (r2 = .949).

Analysis of Variance↗
PubMedDate not supplied

[Separation of the enzyme catalyzing polymerization of deoxyribonucleoside diphosphates from preparations of E. coli DNA-polymerase I].

The enzyme which catalyses template independent synthesis of polydeoxynucleotides from deoxynucleoside diphosphates was separated from E. coli DNA polymerase I by DEAE-cellulose chromatography followed by ultrafiltration through the M-50 Amicon filter. The ultrafiltration data indicate that the molecular weight of the enzyme is not higher than 50,000. The enzyme is not able to use deoxynucleoside triphosphates, ribonucleoside di- or triphosphates as substrates for the polymerization. The reaction of template independent polymerization proceeds with a lag period varying from 2 to 20 hours (for different preparations of enzyme) and is activated by Mg2+ (the optimal concentration 1-2 . 10(-3) M). The pH optimum of the reaction is at 8.5. The optimal concentration of deoxyribonucleoside diphosphates is 10(-3) M, and its increase strongly inhibits polymerization. The enzyme was supposed to be called deoxynucleoside diphosphate: olygonucleotide deoxynucleotidyltransferase (catalyzing polymerization without template). The presence of the enzyme in the preparations of E. coli DNA-polymerase I can explain the ability of the latter to catalyze the untemplated synthesis of poly dG : poly dC.

DNA Polymerase I↗
PubMed1993

Molecular basis of the inhibition of beta s-chain-dependent polymerization by mouse alpha-chain. Semisynthesis of chimeras of human and mouse alpha-chains.

The transgenic mouse models expressing beta s-globin genes do not fully exhibit the sickling phenotype, primarily as a result of the inhibition of beta s-chain-dependent polymerization by the mouse alpha-chains. The mouse alpha-chain differs from the human alpha-chain at 19 sequence locations. Of these, only alpha 78 and alpha 116 are the known hemoglobin (Hb) S polymer contact sites. To define whether the inhibition of polymerization by the mouse alpha-chain is solely a consequence of the differences at these two sites or additional sites of sequence differences are also involved, we have constructed chimeric alpha-chains by employing the alpha-globin semisynthetic reaction (Sahni, G., Cho, Y. J., Iyer, K. S., Khan, S. A., Seetharam, R., and Acharya, A. S. (1989) Biochemistry 28, 5456-5461). Mouse alpha 1-30 was spliced with human alpha 31-141 using endoproteinase Glu-C to generate a chimeric alpha-globin (alpha MH) containing eight of the 19 sequence differences of mouse alpha-globin. Similarly, human alpha 1-30 was spliced with mouse alpha 31-141 to generate another chimeric alpha-globin (alpha HM) containing 11 sequence differences. The respective chimeric globins were purified, reconstituted with heme and beta s-chain into tetrameric hemoglobin, and the tetramers were purified by ion-exchange chromatography. The inhibitory potential of the chimeric alpha MH-chain on the polymerization is 10-fold lower than that of the mouse alpha-chain. The absence of the alpha 31-141 region of the mouse alpha-chain relieves only a portion of the inhibition. The inhibitory potential of alpha MH contributed by the mouse alpha 1-30 segment is significant although none of the sequence differences in this segment are located at any of the implicated polymer contact sites. The chimeric alpha HM-chain also inhibits the polymerization, but the extent of inhibition is again lower (4-fold) than that of the full-length mouse alpha-chain. The results demonstrate that the inhibitory potential of mouse alpha-chains involves the sequence differences from both the alpha 1-30 and alpha 31-141 regions. Besides, since the sum of the inhibitory potential of either of these chimeric alpha-chains is lower than that of the intact mouse alpha-chains, we speculate that conformational changes that require the copresence of sequence differences in both portions of the mouse alpha-chain also contribute to the inhibitory propensity of the mouse alpha-chain.

Animals↗