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PubMed1975

Ionic and nucleotide requirements for microtubule polymerization in vitro.

The ionic and nucleotide requirements for the in vitro polymerization of microtubules from purified brain tubulin have been characterized by viscometry. Protein was purified by successive cycles of a temperature dependent assembly-diassembly scheme. Maximal polymerization occurred at a concentration of 0.1 M Pipes (piperazine-N,N'-bis(2-ethanesulfonic acid)); increasing ionic strength by addition of NaCl to samples prepared in lower buffer concentrations did not result in an equivalent level of polymerization. Both Na-+ and K-+ inhibited microtubule formation at levels greater than 240 mM, withmaximal assembly occurring at physiological concentrations of 150 mM. Maximal extent of assembly occurred at pH 6.8 and optimal rate at pH 6.6. Inhibition of polymerization was half-maximal at added calcium concentrations of 1.0 mM and magnesium concentrations of 10.0 mM. EGTA (ethylene glycol bis(beta-aminoethyl ether)tetraacetic acid), which chelates Ca-2+, had no effect on polymerization over a concentration range of 0.01-10.0 mM. In contrast, EDTA (ethylenediaminetetraacetic acid), which chelates both Mg-2+ and Ca-2+, inhibited assemble half-maximally at 0.25 mM and totally at 2.0 mM. As determined from experiments using Mg-2+-EDTA buffers, magnesium was required for polymerization. Magnesium promoted the maximal extent of assembly at substoichiometric levels relative to tubulin, but was maximal for both rate and extent at stoichiometric concentrations. Elemental analyses indicated that approximately 1 mol of magnesium was tightly bound/mol of tubulin dimer. Viscosity development was dependent upon hydrolyzable nucleoside triphosphate, and stoichiometric levels of GTP were sufficient for maximal polymerization. The effect of magnesium in increasing the rate of GTP-dependent polymerization suggests that a Mg-2+-GTP complex is the substrate required for a step in assembly.

Alkanesulfonates↗
PubMed1977

Physiological regulation of total tubulin and polymerized tubulin in tissues.

Polymerized and depolymerized forms of tubulin were measured in rat and mouse liver, rat islets, human lymphocytes, and platelets. The percent of the total tubulin present in the polymerized form varied from 30.3 +/- 1.5% in the liver of the fed rat to 89.2 +/- 0.2% in human platelets. Fasting decreased the total tubulin and to a greater extent the polymerized form of tubulin in both rat and mouse liver. Glucose feeding increased the polymerized tubulin without affecting the total tubulin content in rat liver. Phytohemagglutinin-stimulated lymphocytes exhibited at least a three-fold increase in total tubulin (expressed in terms of DNA content), which during the initial 48 h of incubation was accounted for in toto by an increase in polymerized tubulin. It is suggested that the lectin not only accelerates tubulin synthesis but also stimulated the polymerization process. Storage of platelets at 4 degrees C for 6 days resulted in a marked decrease in total tubulin and an even greater reduction in the polymerized form. It is concluded that both the total tubulin content and its degree of polymerization can be modulated independently by a wide variety of physiological factors.

Animals↗
PubMed1979

Seeding role of spectrin in polymerization of skeletal muscle actin.

The effect of spectrin on the polymerization of muscle actin has been investigated by hydrodynamic methods and electron microscopy. Spectrin markedly accelerated polymerization of actin. The effect was more easily observed in lower concentrations of KCl (e.g. 24 mM) where spontaneous polymerization was negligibly small. Similarly large acceleration was observed for polymerization in MgCl2 or CaCl2. The rate of polymerization of actin was proportionally increased with the concentration of spectrin added to a fixed concentration of action. The stationary level of specific viscosity also increased with the spectrin concentration, but at larger concentrations it became smaller. The flow birefringence and electron microscope measurements indicated that actin polymers formed under the influence of spectrin were shorter than those of control F-actin filaments. The structural viscosity and electron microscope observations suggested that the interaction between F-actin fibers was not increased by spectrin. These data strongly suggest a seeding role of spectrin in the polymerization of actin. Spectrin accelerates formation of the nuclei for polymerization. The more the nuclei are formed, the larger the number of the grown polymers are and this leads to rapid formation of shorter polymers since the amount of actin is limited. The acceleration activity was found only in freshly prepared spectrin from fresh ghosts taken from freshly drawn blood.

Actins↗
PubMed1992

Curing light performance and polymerization of composite restorative materials.

The majority of modern composite restorative materials require light activation for polymerization. Variables affecting light energy absorption by the composite have been examined for their effect on the polymerization contraction. Since the polymerization contraction is closely associated in a complex way to the degree of cure of the restoration, this parameter served as an empirical indicator for the extent of polymerization. Variables included the composite shade, distance between the light source and composite sample, and light intensity. Three resin composites are evaluated. Post-gel polymerization contraction was evaluated using a strain gauge method. Curing light intensity diminished rapidly for distances greater than 2 mm between the tip of the light guide and material surface. A linear relationship was demonstrated between polymerization contraction and light intensity. The polymerization contraction of a microfilled composite and posterior composite, using a constant curing time and light intensity, decreased linearly with increasing sample thickness. Less than optimal light output of the curing light source can be compensated by increasing application time within reasonable limits.

Composite Resins↗
PubMed1976

Abnormal fibrin polymerization in liver disease.

Although there have been isolated reports of an acquired abnormal fibrinogen in patients with liver disease, its frequency and clinical significance is not known. In this study 121 consecutive patients with a wide spectrum of hepatic disorders were screened for abnormal fibrin polymerization. A simple colorimetric method using Reptilase was employed. Of 32 patients with proven cirrhosis, 16 (50%) showed abnormal fibrin polymerization. The incidence in decompensated alcoholic cirrhosis was particularly high. The abnormality was also detected in all patients with acute liver failure and seven of 15 with chronic active liver disease. Clinical improvement often correlated with its disappearance. Two patients with primary liver cell tumours demonstrated the abnormal polymerization. In patients with bleeding oesophageal varices the detection of abnormal fibrin polymerization was associated with a poor prognosis. None of the patients with surgical obstructive jaundice (26) or miscellaneous liver disorders (37) had abnormal fibrin polymerization. The occurrence of abnormal fibrin polymerization in liver disease is more frequent than previously suspected and usually signifies severe primary hepatocellular dysfunction. Evidence is presented to support the presence of a primary abnormality of fibrinogen as the cause of impaired fibrin monomer polymerization.

Batroxobin↗
PubMed1992

The effect of polymerization shrinkage during veneer placement.

This study evaluated the relationship of polymerization shrinkage during composite resin veneer placement to direction of the polymerization light source. Fifty maxillary permanent incisors were obtained and divided into five groups of ten. Groups I and II had preparations placed in enamel. Groups III, IV, and V had preparations placed in dentin. In groups I and III, an unfilled bonding resin was placed and polymerized from the facial aspect, followed by placement and polymerization of a hybrid composite resin. Groups II and IV were initially polymerized from the lingual direction. In group V, the unfilled resin and hybrid composite resin were polymerized simultaneously from the facial aspect. Statistical analysis indicated that there was significantly less axial microgap formation during lingual polymerization when the preparation remained in dentin, but demonstrated that there was no statistically significant difference when the preparation remained in enamel.

Analysis of Variance↗
PubMed1992

Lymphoblastoid cell adhesion mediated by a dimeric and polymeric endogenous beta-galactoside-binding lectin (galaptin).

Glutaraldehyde-polymerized human splenic galaptin, a beta-galactoside-binding lectin, was demonstrated to have enhanced hemagglutinating and asialofetuin binding activity relative to native dimeric galaptin when these lectins were present in solution. The polymerized lectin consisted primarily of 2-, 4- and 12-membered species after reductive alkylation. Both forms of galaptin bound, at 4 degrees C, to saturable B lymphoblastoid cell surface receptors. Estimates obtained by Scatchard analyses, with the binding data expressed in terms of 14.5 kDa subunit molarity, were 5 x 10(7) binding sites/cell with affinity constant Ka = 2.2 x 10(5) M for dimeric galaptin and 17 x 10(7) binding sites/cell with Ka = 3.4 x 10(5) M-1 for polymeric galaptin. Both forms of galaptin adsorbed to polystyrene with high efficiency; however, only plastic-adsorbed polymeric galaptin mediated adhesion of lymphoblastoid cells. Cell adhesion was inhibited by lactose. Plastic-adsorbed polymeric galaptin bound asialofetuin more efficiently than dimeric galaptin. Asialofetuin binding was inhibited 65% and 30-50% by lactose for plastic-adsorbed polymeric and dimeric galaptin, respectively. Native fetuin bound to the adsorbed dimeric galaptin in a lactose-insensitive manner. These data indicate that cell surface receptor-galaptin interaction is carbohydrate specific whereas polystyrene-adsorbed galaptin may demonstrate protein-protein interactions with soluble ligands.

Asialoglycoproteins↗
PubMed1992

Stimulus-dependent actin polymerization in bovine neutrophils.

Polymorphonuclear leukocytes (PMNs) are responsible for much of the first wave of leukocyte-mediated host defense against microbial pathogens. In order to migrate through the endothelium of vessel walls, undergo chemotaxis, and phagocytize microbes, PMNs must modulate their cytoskeletal elements and undergo change of cellular shape. We have used fluorescence flow cytometric analysis and cellular microscopic observations to demonstrate actin polymerization in bovine PMNs and to examine the kinetics of PMN actin polymerization utilizing different PMN stimuli. In addition, we compared temporal relationships between cellular shape and actin polymerization. Actin polymerization occurred rapidly, and the kinetics of actin polymerization were similar for each of the three PMN agonists used, ZAS (10%), PAF (10(-6) M), and rhC5a (10(-7) M). Actin polymerization was near-maximal by 10 sec poststimulation (95.4% of maximal F-actin content attained by 10 sec poststimulation with ZAS stimulation), and reached peak values by 30 sec. The maximal increase in F-actin content of agonist-stimulated cells as compared to resting cells was 2.8-fold with ZAS; 2.3-fold with PAF; and 2.3-fold with rhC5a. PMN shape change (pseudopodia, membrane ruffles) was not as rapid, with only 22.4% of cells attaining visible membrane deformation by 10 sec and requiring 120 sec to reach peak shape-change values. After attaining peak values, the two events also differed. Whereas the percent of shape-changed PMNs remained plateaued up to 5 min poststimulation, the F-actin content gradually decreased after 30 sec, approaching F-actin values of unstimulated PMNs.

Actins↗
PubMed1976

Observations on the different substrate behavior of tropocollagen molecules in solution and intermolecularly cross-linked tropocollagen within insoluble polymeric collagen fibrils.

Bacterial collagenase was used to compare the extent of digestion of tropocollagen monomers in solution and in reconstituted fibrils with that of tropocollagen molecules intermolecularly cross-linked within insoluble polymeric collagen fibrils obtained from mature tendons at given time-intervals. The extent of digestion of tropocollagen monomers in solution was directly proportional to the enzyme concentration (a range of enzyme substrate molar ratios 1:200 to 1:10 was used). The extent of digestion of polymeric collagen was followed by measuring the solubilization of fluorescent peptides from fluorescent-labelled insoluble polymeric collagen fibrils. The extent of digestion of tropocollagen within polymeric collagen was linear over a very small range of enzyme concentrations, when the enzyme/substrate ratio in the reaction mixture was less than 1:400 on a molecular basis. The behavior of tropocollagen in the form of reconstituted collagen fibrils, which had been matured at 37 degrees C for 8 weeks, was intermediate between the behaviour of solutions of tropocollagen and insoluble polymeric collagen fibrils. The significance of the results is discussed in terms of the structure of polymeric collagen fibrils and the protection against enzymic attack provided by tropocollagen molecules on the circumference of the fibril. The results suggest that assays of collagenase activities based on tropocollagen as substrate cannot be directly related to the ability of these enzymes to degrade mature insoluble collagen fibrils.

Animals↗
PubMed1976

Comparison of polymerized and unpolymerized antigen E for immunotherapy of ragweed allergy.

Polymerization of ragweed antigen into high-molecular-weight polymers could improve immunotherapy for ragweed pollinosis by reducing side effects while retaining immunogenicity. To study this thesis, 23 ragweed-sensitive patients were treated with either ordinary ragweed antigen E or ragweed antingen E polymerized by glutaraldehyde. Four patients received the polymerized antigen, and six controls ordinary antigen according to the standard immunotherapy schedule; two groups of three patients received either form by a "doubling-dose" schedule. Seven subjects received the polymerized antigen by a schedule in which each successive dose was tripled. Serum antigen E binding capacity (blocking antibody) increased significantly in all subjects (P less than 0.001 by Student-test). Patients treated with polymerized antigen had fewer local and generalized reactions than those receiving the monomeric preparation. Polymerized ragweed antigen permits more rapid immunization of atopic persons, with fewer side effects than standard monomeric preparations.

Adult↗
PubMed1978

Role of nucleotides in tubulin polymerization: effect of guanosine 5'-methylene diphosphonate.

Incubation of purified rat brain tubulin with guanosine 5'-methylene diphosphonate [GMP(CH2)P] (1 mM), a GDP analog resistant to hydrolysis, results in the polymerization of 20-30% of the total tubulin present. Analogous incubations with GDP (1 mM) do not result in tubulin polymerization. Polymerization with GMP(CH2)P occurs in the presence of alkaline phosphatase (EC 3.1.3.1) under conditions that completely hydrolyze the likely phosphate donors (GTP, GDP, and GMP) as well as the potential product [GMP(CH2)PP] of the transphosphorylase activity present in purified tubulin preparations. Tubulin polymerization in vitro thus can occur in the absence of gamma-phosphate and phosphate bond hydrolysis at the exchangeable nucleotide-binding site of tubulin. Polymerization of tubulin by GMP(CH2)P is neither prevented nor reversed by concentrations of calcium (2 mM) that prevent microtubule assembly and disrupt already formed microtubules induced by GTP. However, tubulin polymerized with GMP(CH2)P is readily depolymerized by cold (4 degrees, 30 min). The possible involvement of GTP alpha-beta bond hydrolysis must be considered seriously as playing a role in the process of microtubule depolymerization.

Alkaline Phosphatase↗
PubMed1992

Actin-actin contact: inhibition of actin-polymerization by subdomain 4 peptide fragments.

F-Actin was digested with alpha-chymotrypsin in 6 M urea, and two peptide fragments from subdomain 4 of actin molecule [Kabsch, W., Mannherz, H.G., Suck, D., Pai, E.F., & Holmes K.C. (1990) Nature 347, 37-44] were purified by reverse-phase HPLC and Sephadex G-50 gel filtration. The peptide fragments were identified as segments from Arg-177 to Tyr-198 (2.6-kDa peptide) and from Ser-199 to Tyr-279 (9.1-kDa peptide). Their effects on actin polymerization induced by 50 or 100 mM KCl were studied by measuring the increase in viscosity by the falling ball method. The 2.6-kDa peptide decreased the rate of actin polymerization and increased the critical concentration for the polymerization. Based on the atomic model of the actin filament [Holmes, K.C., Popp, D., Gebhard, W., & Kabsch, W. (1990) Nature 347, 44-49], the peptide is presumed to bind to the barbed end of the actin filament and inhibit the polymerization. By assuming that the peptide affected the rate of association of the actin monomer to the end of the actin filament, well-fitting curves for the polymerization kinetics were calculated. Computer-assisted results indicated that the dissociation constant of the 2.6-kDa peptide for F-actin is 200 to 260 microM. In contrast, the 9.1-kDa peptide only slightly inhibited actin polymerization. These results suggest that the actin-actin interface in the region between Arg-177 and Tyr-198 has a stronger interaction than those between Ser-199 and Tyr-279. The amino acid sequence L-T-D-Y-L present in the 2.6-kDa segment is homologous to a common sequence in the F-actin capping domain of various actin-binding proteins.

Actins↗
PubMed1976

Relationship between paraprotein polymerization and clinical features in IgA myeloma.

The clinical manifestation fo IgA multiple myeloma are usually not considered distinguishable from those of IgG myeloma despite the fact that IgA differs from IgG in several characteristics, particularly molecular size heterogeneity. The clinical and laboratory features of 25 patients with IgA myeloma seen during a 5 year period are presented. The degree of paraprotein polymerization was observed to vary greatly in these patients but remained chronologically constant in six individuals studied on several occasions over this period. The patients were divided into two groups on the basis of the degree of paraprotein polymerization. The first group comprised those patients in whom the IgA paraprotein was greater than 50% polymerized, whilst in the second group the paraprotein was predominantly monomeric. No clinical or pathological differences were seen between the 'polymeric' and 'monomeric' groups of myeloma apart from that directly attributable to the physicochemical effect of the paraprotein polymerization. Thus, five patients out of 11 of the 'polymeric' group had developed the hyperviscosity syndrome, whilst no patients in the 'monomeric' group had developed this complication. The concentration of the paraprotein during the course of the disease was comparable in both groups. This syndrome is considered to be relatively common in IgA myeloma and adds to the morbidity and mortality of the disease. Its anticipation and treatment may improve the quality and survival of patients likely to develop this complication.

Adult↗
PubMedDate not supplied

Improved diagnostics: clinical evaluation of a color-coded, polymeric periodontal probe.

The objective of this study was to compare the accuracy, reproducibility and patient comfort of a newly designed, color-coded, polymeric periodontal probe to a traditional, color-coded metal probe. Twenty-four adult subjects with varying degrees of periodontal disease (from slight to severe) reported for two visits, one week apart. A randomization schedule for probe use was adopted over the two visits so that the gingival crevices in two quadrants were probed with the same probe (metal or polymeric) providing reproducibility information for each probe, while the other two quadrants were probed first with one probe then the other for comparison data yielding information on accuracy. A bleeding index was obtained using the same schedule. Clinical scoring was performed by the same examiner. After probing each quadrant, subjects rated discomfort using a visual analog scale (VAS). Results showed no significant difference in depth readings greater than 2 mm between the polymeric and metal probes (3.41 +/- 0.37 mm vs. 3.38 +/- 0.32 mm, p = 0.55). Significantly less discomfort (assessed by VAS) was recorded by patients after polymeric probe use (3.70 +/- 2.40 cm vs. 4.44 +/- 2.49 cm, p = 0.015). The bleeding index indicated significantly less bleeding with the polymeric probe (0.80 +/- 0.56 vs. 1.24 +/- 0.65, p = 0.0001). Both the polymeric and metal probes were found to produce highly reproducible results in all measures across visits.

Adult↗
PubMed1978

[Polymerization shrinkage and fitness of denture (author's transl)].

Polymerization shrinkage causes dimensional change of denture during the processing. We can not control the amount of shrinkage but can control the initiation points and the direction of polymerization. Heat conductivities of dough and mould, the distance from heating or cooling place, and amount of MMA etc. have influence on the polymerization. Polymerization shrinkage mainly appears on the point where polymerize last. In the case of heat processing the shrinkage mainly appeared on the point where heat supply was slow. On the other hand in that of self-curing resin, the polymerization starts at the center of the mass when the mould is immersed in an ice water bath and the shrinkage appeared on the surface of mass. Dentures were prepared by heat processing resin conventionally heated in a water bath, heated from mucous side only on a heat plate, and self-curing fluid resin. An amount of filled light body silicone impression materials between the denture and cast was minimum in the case of the one side heat processed denture. That was middle in the self-cured. The maximum case was conventional heat cured denture.

Composite Resins↗
PubMed1992

Thrombin, epidermal growth factor, and phorbol myristate acetate stimulate tubulin polymerization in quiescent cells: a potential link to mitogenesis.

Previous studies suggest that alterations in the microtubule (MT)-tubulin equilibrium during G0/G1 affect mitogenesis. To determine the effect of growth factors on the MT-tubulin equilibrium, we developed a radioactive monoclonal antibody binding assay (Ball et al.: J. Cell. Biol. 103:1033-1041, 1986). With this assay, 3H-Ab 1-1.1 binding to cytoskeletons in confluent populations of cultured cells is proportional to the number of tubulin subunits polymerized into MTs. We now show that purified alpha-thrombin increases 3H-Ab 1-1.1 binding to cytoskeletons of serum-arrested mouse embryo (ME) fibroblasts from 1.5- to 3-fold. This stimulation is dose-dependent and correlates with concentrations of thrombin required for initiation of DNA synthesis. Other mitogenic factors, epidermal growth factor (EGF) and phorbol 12-myristate 13-acetate (PMA), also stimulate MT polymerization. Addition of colchicine (0.3 microM) eight hours after growth factor addition, blocks stimulation of 3H-thymidine incorporation by thrombin, EGF, or PMA, suggesting that tubulin polymerization or subsequent events triggered by MT polymerization are required for cells to enter a proliferative cycle. Consistent with models for autoregulation of tubulin synthesis, thrombin, EGF, and PMA all increase tubulin synthesis 9 to 15 hr after growth factor addition, raising the possibility that the decrease in free tubulin and subsequent stimulation of tubulin synthesis is linked to progression of cells into a proliferative cycle. Colchicine addition to these cells also stimulates DNA synthesis, but colchicine-stimulated cells enter S phase 6 to 8 hr later than those stimulated by growth factors. This delayed stimulation may be related to the time required for degradation of tubulin-colchicine complexes below a critical level. These data suggest that regulation of cell proliferation may be linked to increased MT polymerization and the resulting decrease in free tubulin pools.

Animals↗
PubMed1992

Actin polymerization contributes to neutrophil chemotactic dysfunction following thermal injury.

The agent(s) and mechanism(s) responsible for suppression of neutrophil chemotaxis in association with major thermal injury have not been identified. We have proposed that the reduced random motility characterizing patients' cells may contribute to their generalized chemotactic dysfunction. Here we report that actin polymerization may be responsible for the loss of neutrophil motility associated with major thermal injury. Using a fluorescent ligand specific for polymerized or filamentous actin (NBD-phallacidin) in conjunction with flow cytometry, we have discovered that peripheral blood and exudate neutrophils from patients with major thermal injury contain increased levels of actin in a stably polymerized form. Because cyclic polymerization and depolymerization of actin is essential to cell motility, we suggest that actin polymerization may contribute in a major way to the attenuation of neutrophil random and chemotactic functions induced by major thermal injury.

Actin Cytoskeleton↗
PubMed1979

Interaction of hepatitis B surface antigen with polymerized human serum albumin.

HBsAg binds to a solid-phase adsorbent consisting of polymerized human serum albumin (HSA) on glass particles. Both AD and AY antigenic subtypes of hepatitis B surface antigen (HBsAg) display this interaction. In either case, the binding to polymerized HSA is reduced in the presence of human serum, suggesting significant attachment of serum components at the locations on HBsAg particles where polymerized HSA binds. The temperature dependence of the interaction goes through a maximum above room temperature, in contrast to the increasing reaction with temperature of the HBsAg--anti-HBs antibody system. The interaction between HBsAg and polymerized HSA is discussed in relation to previous findings of HSA polymers and anti-polymerized albumin antibodies in hepatic patients. A mechanism for production of an autoimmune, antialbumin antibody condition, in association with hepatitis B virus infection is proposed.

Antibody Specificity↗