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At least 1,531 records · Page 85Linked to original sources
PubMed1980

Enzymatic addition of modified cytosine nucleotides to DNA. Methacrylate polymerization by an azo pyrimidine.

An azo pyrimidine that induces the polymerization of 1-glyceryl methacrylate has been prepared. 1-Glyceryl methacrylate contains substituent glycol groups for binding heavy atoms for subsequent electron microscopic studies. Oxodation of 1-methyl N4-ureidocytosine (compound 1A) with N-bromosuccinimide produced 4-aminocarbonylazo-2-pyrimidinone (compound 2A). This orange compound shows a broad peak (lambda max = 349 nm) in its ultraviolet absorption spectrum. Mixing compound 2A with mildly acidic aqueous solutions of 1-glyceryl methacrylate (pH 3.6) resulted in polymerization of the methacrylate. Under these conditions, the ester 1-glyceryl methacrylate does not hydrolyze appreciably as judged by oxidation of the glycol groups with NaIO4 and spectrophotometric analysis of the HCHO liberated using Schiff's reagent. Attachment of azo nucleotides to the 3'-terminus of DNA was achieved in two steps. First, N4-ureidocytosine deoxynucleotides were enzymatically added to single strand DNA primers using calf thymus terminal deoxynucleotidyl transferase, Co2+, and N4-ureido-2'-deoxycytidine 5'-triphosphate (prepared by the HSO3--catalyzed transamination reaction of dCTP with semicarbazide). Second, these modified nucleotides were oxidized with N-bromosuccinimide to produce DNA that contained azo pyrimidine nucleotides at its 3'-end (azoDNA). Upon adding acid to the azoDNA, the azo nucleotides decomposed. If these nucleotides induce methacrylate polymerization upon decomposition as did compound 2A, it may be possible to mark the location of DNA termini in situ for electron microscopy by attaching heavy atoms to the poly(1-glyceryl methacrylate) formed. Such studies may elucidate the nature and location of the ends of the eukaryotic chromosomal DNA molecule in both chromosomes and interphase nuclei.

Acrylic Resins↗
PubMed1976

The influences of divalent metal ions on fibrin monomer polymerization.

This work was undertaken in an attempt to clarify the influences of divalent metal ions on the polymerization of fibrin monomer. Polymerization was strongly inhibited by such Ca-binding chelating agents as 1,2-cyclohexanediaminetetraacetic acid, ethylenediaminetetraacetic acid and glycoletherdiaminetetraacetic acid, and a close relationship was seen between their inhibitory capacity and their stability against Ca2+. The polymerization inhibited by ethylenediaminetetraacetic acid could not be reversed by the addition of Mg2+, Sr2+ or Ba2+, whose stability constants are smaller than that of Ca2+, but it could be completely reversed, and even directly accelerated by Zn2+, Cu2+, Cd2+ or Co2+ whose stability constants are greater than that of Ca2+.

Barium↗
PubMed1977

The polymerization pattern of zinc(II)-insulin at pH 7.0.

Sedimentation equilibrium experiments were conducted at pH 7.0 using solutions of bovine insulin containing 2 mol of zinc(II) ions per six base-mol of insulin. A detailed analysis of these results revealed the existence of a stable zinc-insulin hexamer together with linked polymerization reactions. Specifically these are a background polymerization of zinc-free insulin as previously described by Jeffrey et al. ((1976) Biochemistry 15, 4660--4665) and a slight tendency for the zinc-insulin hexamer to undergo indefinite self-association. Equilibrium constants governing these reactions are reported together with equations which permit calculation of the composition of the solution at any given total concentration. Comment is made on the possible biological significance of this linked polymerization pattern, and on the likely identity of the structure of the stable zinc-insulin hexamer with that previously reported from X-ray crystallographic studies.

Animals↗
PubMed1978

Polymerization and colchicine binding. Two independent properties of tubulin.

When stored frozen in 1 M sucrose and 1 mM GTP, tubulin loses polymerizing ability exponentially. Since addition of diethiothreitol does not change the decay half-life, this decrease in activity can not be attributed to disulfide bond formation. When tubulin is stored frozen in dithiothreitol and GTP only, the decay half-life increases by a factor of four, indicating that sucrose destabilizes polymerizing ability. Frozen storage in sucrose has the opposite effect on colchicine binding, which remains at 100% for 40 days. This temporal divergence indicates that colchine binding and polymerization are two independent properties of tubulin.

Animals↗
PubMed1983

Isolation of an actin polymerization stimulator from bovine thyroid plasma membranes.

An actin polymerization stimulator was purified from bovine thyroid plasma membranes by DNase I affinity column chromatography. Although the molecular weight of the protein was about 42,000 (42K) by sodium dodecyl sulfate polyacrylamide gel electrophoresis, it did not comigrate with actin. In the presence of 30 mM KC1, the 42K protein facilitated formation of actin filaments when analyzed by a centrifugation method, accelerated the initial phase of actin polymerization as measured in an Ostwald viscometer and increased the length of filaments as shown by electron microscopy. The 42K protein also accelerated the initial phase of actin polymerization in the presence of 100 mM KC1 and 2 mM MgCl2 but did not affect the final viscosity. The effect of the 42K protein was diminished by 5 uM cytochalasin B or 1 uM cytochalasin D. This 42K protein may anchor actin filaments onto the thyroid plasma membrane.

Actins↗
PubMed1985

Stimulation of the Ca2+-dependent polymerization of synexin by cis-unsaturated fatty acids.

The influence of fatty acids on the polymerization of synexin was studied by monitoring light scattered from solutions of purified synexin. Cis-unsaturated fatty acids such as arachidonate or oleate stimulated synexin polymerization at sub-micromolar concentrations, while saturated fatty acids, a trans unsaturated fatty acid or a fatty acid methyl ester had little effect. The polymerization of synexin occurred at lower concentrations of Ca2+ in the presence of the fatty acids than in the absence of fatty acids. Therefore, Ca2+ and free fatty acids may act as co-regulators of synexin action in stimulated secretory cells.

Animals↗
PubMed1987

Bull sperm 19S dynein polymerizes brain tubulin into microtubules.

Crude dynein extracted from bull sperm flagella polymerized pure phosphocellulose tubulin isolated from brain tissues into microtubules. This effect was predominantly due to the 19S dynein particle in the extract. ATP stimulated up to five fold the polymerization of brain tubulin by bull sperm dynein. Hydrolysis of ATP was not required since vanadate at a concentration sufficient to block dynein ATPase activity did not interfere with ATP stimulation and because the non hydrolyzable ATP analogue adenylyl (beta-gamma-methylene) diphosphate (AMPPCP) had effects similar to those of ATP. These results suggest that, in addition to hydrolyzing ATP to generate the driving force necessary for microtubule sliding within the axoneme, dynein may also interact with ATP to polymerize tubulin into microtubules.

Adenosine Triphosphatases↗
PubMed1989

Polymerization of factor B of the alternative complement pathway via disulfide bond(s) in the presence of Cu2+ and stimulation by C3b, the major fragment of C3.

Factor B(B) of the alternative complement pathway has been found to dimerize via disulfide bond(s) in the presence of CuCl2. Poly B has no B activity. The Bb fragment was also dimerized, indicating that one free sulfhydryl group on the Bb portion might be involved in polymerization. The Ba fragment was not dimerized. C3b, the major fragment of C3, has the capacity to stimulate polymerization of B. Incubation of C3b, B and factor D in the presence of Mg2+ and Cu2+ resulted in the formation of poly B and diminished cleavage of B. These results suggest that polymerization of B due to Cu2+ might be partly responsible for the impairment of C3 convertase activity of the alternative pathway.

Complement C3↗
PubMed1991

Thermal polymerization of some glucofuranose derivatives.

Methyl alpha,beta-D-glucofuranoside (1) and 1,2-O-isopropylidene-alpha-D-glucofuranose (2) have been polymerized thermally, using 0.1% phosphoric acid as catalyst. The resulting alcohol-insoluble polymers were analyzed by gel-permeation chromatography and methylation analysis. The two starting materials gave polymers that were very similar in molecular-weight distribution and in glycosyl-linkage composition. The proportion of furanosyl residues in the polymer, estimated by the relative proportions of furanosyl and pyranosyl residues that could be determined unequivocally by methylation analysis, was approximately 35-40%; higher than is found when glucopyranosides are polymerized, but indicating that significant furanose-pyranose isomerization had occurred during the polymerization process.

Catalysis↗
PubMed1984

Angiotensin II stimulation of granuloma macrophage phagocytosis and actin polymerization in murine schistosomiasis mansoni.

In murine schistosomiasis, components of the renin-angiotensin system are present in isolated liver granulomas. Furthermore, granuloma macrophages have receptors for angiotensin II (AII). These observations with other evidence suggest that angiotensins function in immunoregulation. Since AII can stimulate actin-myosin interactions and since macrophages have contractile proteins, it was determined whether AII could alter the phagocytic activity of granuloma macrophages. AII, at concentrations which saturate AII receptors, enhanced phagocytic activity for both unopsonized and opsonized sheep red blood cells (RBC). Using a DNase inhibitory assay, it was also shown that similar concentrations of AII stimulated intracellular actin polymerization. Cytochalasin B, which impedes actin filament interactions, inhibited AII-stimulated phagocytosis. AII analogs, with little-known agonist activity, blocked AII-stimulated actin polymerization and phagocytosis of RBC and RBC opsonized with IgG. These data support the contention that AII binds to AII receptors on the macrophage and stimulates phagocytosis possibly through polymerization of intracellular actin.

Actins↗
PubMed1983

Spreading and polymerization behavior of diacetylenic phospholipids at the gas-water interface.

A variety of polymerizable lipids derived from hexacosa-10,12-diynoic acid and hexacosa-10,12-diyne-1-ol have been synthesized and spread at the gas/water interface. The measured surface pressure/area isotherms indicate that head group charge and bulkiness have strong influences on the area occupied per molecule. In the case of zwitterionic phospholipids additional area changes are brought about by alkaline and acidic subphases, which is probably due to an alteration of head group conformation. Condensed state diacetylenic lipid monolayers in a nitrogen atmosphere are polymerizable by UV irradiation. The polymerization reaction was monitored at the gas/water interface by the area change at constant surface pressure and the change of optical density in the visible region. As already observed for vesicle polymerization, single chain amphiphiles exhibit a different absorption behavior than asymmetric double chain amphiphiles of the phosphoglycerol type. The polymerized monolayers were more densely packed and more stable than their monomeric counterparts as indicated by the smaller areas and higher pressures reached before the collapse points.

Alkynes↗
PubMed1987

Botulinum C2 toxin potentiates activation of the neutrophil oxidase. Further evidence of a role for actin polymerization.

Botulinum C2 toxin was employed as a specific inhibitor of actin polymerization in rat neutrophils to determine its role in oxidase activation. This toxin was shown to inhibit actin polymerization and the microfilament-dependent function, phagocytosis. Oxidase activation in response to the chemotactic peptide, f-Met-Leu-Phe (FMLP) was enhanced approx. 3-fold. The enhancement by C2 toxin did not occur in cells pretreated with cytochalasin B. C2 toxin had no significant effect on the FMLP-induced intracellular Ca2+ rise. These data are consistent with an inhibitory role for actin polymerization in oxidase activation.

Actins↗
PubMed1996

Binding of matrix attachment regions to nuclear lamin is mediated by the rod domain and depends on the lamin polymerization state.

The nuclear matrix maintains specific interactions with genomic DNA at sites known as matrix attachment regions (M/SARs). M/SARs bind in vitro to lamin polymers. We show that the polymerized alpha-helical rod domain of lamin Dm0 provides by itself the specific binding to the ftz M/SAR. In contrast, unpolymerized rod domain does not bind specifically to this M/SAR. Non-specific binding to DNA is also observed with Dm0 containing a point mutation that impairs its ability to polymerize or with the isolated tail domain. These data suggest that the specific binding of lamins to M/SARs requires the rod domain and depends on the lamin polymerization state.

Amino Acid Sequence↗
PubMed1996

Formation of polymeric chelate bridges between double-stranded DNA molecules fixed in spatial structure of liquid-crystalline dispersions.

The formation of cholesteric liquid-crystalline dispersions from DNA-daunomycin complexes in water-salt polyethyleneglycol-containing solutions was investigated. In the case of nonclassical complex formation between DNA and daunomycin (DAU), reactive groups of DAU were used for the formation of polymeric chelate complex with divalent copper ions (-DAU-Cu-...-Cu-DAU-), located between neighboring double-stranded DNA molecules, fixed in spatial structure of liquid-crystalline dispersions. The formation of polymeric chelate complex does not depend upon the sense of helicoidal twist of DNA cholesterics. A many-fold increase in the CD band in the DAU absorption region is specific to this process. A reduction of the divalent copper ions as a result of a redox-process is accompanied by destroying of structure of polymeric chelate complex between DNA molecules and by disappearance of the abnormal CD band in daunomycin absorption region.

Ascorbic Acid↗
PubMed1992

Expression of the polymeric immunoglobulin receptor by cultured aged rat hepatocytes.

The Fischer rat shows an age-related loss of both hepatic blood to bile transport and secretory component-specific binding sites for polymeric immunoglobulin (Ig) A. This age-related loss of hepatic IgA receptor function is also shown by cultured hepatocytes. It is reported here that compared with young cells, binding and uptake of 125I-polymeric IgA by cultured hepatocytes was markedly reduced in cells from senescent animals. In addition, cells from old animals showed markedly diminished secretion of secretory component determined by enzyme-linked immunosorbent assay and expression of polymeric immunoglobulin receptor determined by incorporation of 35S-labeled amino acid and fluorography. It is suggested that the age-related decrease in IgA receptor-mediated transport from serum to bile results, at least in part, from decreased expression and secretion of total hepatic secretory component.

Aging↗
PubMed1995

Uniform-size hydrophobic polymer-based separation media selectively modified with a hydrophilic external polymeric layer.

A simple procedure for the preparation of macroporous hydrophobic styrene-divinylbenzene polymeric separation media with a hydrophilic outer surface has been developed. A hydrophilic monomer and water-soluble polymerization initiator are added to the reaction mixture during the final polymerization step of the preparation of size-monodisperse particles. Because the hydrophobic styrene-divinylbenzene framework of the beads is already formed, and the hydrophilic monomer does not penetrate the pores of the beads that are filled with a hydrophobic porogen, the hydrophilic layer is formed only at the surface of the beads. The hydrophilic monomers used included glycerol monomethacrylate and glycerol dimethacrylate and toluene was used as the porogen for the poly(styrene-co-divinylbenzene) beads. Comparative experiments involving beads with or without a hydrophilic medium showed that the separation selectivity of the media towards hydrophobic solutes remains unchanged. However, the modified medium with a hydrophilic layer could be used to analyse mixtures that also contained large peptide molecules as these do not adsorb at its surface as is the case with the unmodified hydrophobic beads.

Chromatography, Liquid↗
PubMed1985

Chemical potential measurements of deoxyhemoglobin S polymerization. Determination of the phase diagram of an assembling protein.

We have used the "osmotic stress" method to determine the phase diagram of deoxyhemoglobin S polymerization. This method involves equilibration, through a semipermeable membrane, of the protein with solutions of inert polymers of known osmotic pressure. With deoxyhemoglobin A and S solutions, in which we have demonstrated achievement of equilibrium, plots of osmotic pressure versus concentration initially agree closely with the results of other methods of measurement of colligative properties. However, once the known solubility value is exceeded for the deoxyhemoglobin S solutions at various temperatures, there is a rapid rise in hemoglobin concentration over a narrow osmotic pressure range and then a more gradual increase in concentration. We believe that these two regions correspond, respectively, to the onset of the polymerization process, and of subsequent continuing growth and compression or alignment of polymer. We derive the thermodynamic values for these processes and show that the behavior of the deoxyhemoglobin S system is analogous to the phase transition for a simple chemical system. These results are relevant to understanding the intracellular polymerization of deoxyhemoglobin S in sickle cell disease, and these concepts are applicable to other protein assembly systems.

Gels↗
PubMed1988

Scaffolding protein regulates the polymerization of P22 coat subunits into icosahedral shells in vitro.

Coat and scaffolding subunits derived from P22 procapsids have been purified in forms that co-assemble rapidly and efficiently into icosahedral shells in vitro under native conditions. The half-time for this reaction is approximately five minutes at 21 degrees C. The in vitro reaction exhibits the regulated features observed in vivo. Neither coat nor scaffolding subunits alone self-assemble into large structures. Upon mixing the subunits together they polymerize into procapsid-like shells with the in vivo coat and scaffolding protein composition. The subunits in the purified coat protein preparations are monomeric. The scaffolding subunits appear to be monomeric or dimeric. These results confirm that P22 procapsid formation does not proceed through the assembly of a core of scaffolding, which then organizes the coat, but requires copolymerization of coat and scaffolding. To explore the mechanisms of the control of polymerization, shell assembly was examined as a function of the input ratio of scaffolding to coat subunits. The results indicated that scaffolding protein was required for both initiation of shell assembly and continued polymerization. Though procapsids produced in vivo contain about 300 molecules of scaffolding, shells with fewer subunits could be assembled down to a lower limit of about 140 scaffolding subunits per shell. The overall results of these experiments indicate that coat and scaffolding subunits must interact in both the initiation and the growth phases of shell assembly. However, it remains unclear whether during growth the coat and scaffolding subunits form a mixed oligomer prior to adding to the shell or whether this occurs at the growing edge.

Capsid↗