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PubMed2000

Double-blind randomized controlled trial of glutamine-enriched polymeric diet in the treatment of active Crohn's disease.

BACKGROUND: Glutamine is traditionally considered a nonessential amino acid but may be conditionally essential in patients with catabolic conditions. Glutamine-supplemented foods in these patients have been shown to prevent deterioration of gut permeability, protect against the development of intestinal mucosal atrophy, and improve nitrogen balance. Animal models of inflammatory bowel disease suggest that glutamine-enriched enteral diets may lead to less severe intestinal damage, less weight loss, improved nitrogen balance, and reduced disease activity. The purpose of the current study was to compare the efficacy of a glutamine-enriched polymeric diet with a standard low-glutamine polymeric diet in the treatment of active Crohn's disease. METHODS: Eighteen children with active Crohn's disease were randomly assigned to receive a 4-week course of either a standard polymeric diet with a low glutamine content (4% of amino acid composition; group S) or a glutamine-enriched polymeric diet (42% of amino acid composition; Group G). The two diets were isocaloric and isonitrogenous with an identical essential amino acid profile. Remission rates were analysed on an intent-to-treat basis. Changes in clinical and laboratory parameters of disease activity were also compared after 4 weeks of nutritional treatment. RESULTS: Two of the children, both in group G, were withdrawn from the trial because of nontolerance of the diet. There was no difference between the two groups in proportion of patients achieving remission (intent-to-treat basis): 5 (55.5%) of 9 in group S versus 4 (44.4%) of 9 in group G (p = 0.5). Improvement in mean paediatric Crohn's disease activity index (PCDAI) was significantly more in group S (p = 0.002) but changes in orosomucoid level, platelet count, and weight were not different between the groups. CONCLUSIONS: The findings suggest that a glutamine-enriched polymeric diet offers no advantage over a standard low-glutamine polymeric diet in the treatment of active Crohn's disease. Rather, it appears to be less effective in improving PCDAI. The reported beneficial effects of glutamine seen in many catabolic states must be viewed with caution when extrapolating to the management of Crohn's disease.

Acute-Phase Proteins↗
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↗
PubMed1981

Induction of polymerization of purified tubulin by sulfonate buffers. Marked differences between 4-morpholineethanesulfonate (Mes) and 1,4-piperazineethanesulfonate (Pipes).

Interactions of both purified tubulin and microtubule protein (tubulin plus associated proteins) with two commonly used sulfonate buffers were examined. 1,4-Piperazineethanesulfonate (Pipes) and 4-morpholineethanesulfonate (Mes) at high concentrations induce the polymerization of purified tubulin in reactions requiring only buffer, tubulin and GTP. While both reactions were temperature-dependent, cold-reversible and inhibited by GDP, colchicine or Ca2+, there were significant differences between them. Substantially lower tubulin and buffer concentrations were required for Pipes-induced polymerization; and turbidity was much more intense in the Pipes-induced than in the Mes-induced reaction at the same protein concentration. Electron microscopy demonstrated that for the most part typical smooth-walled microtubules were formed in Mes, while aberrant forms were the predominant structures formed in Pipes. When the polymerization of microtubule protein was examined as a function of buffer concentration, biphasic patterns were observed with both Pipes and Mes: polymerization occurred at both low and high, but not intermediate, buffer concentrations. The turbidity observed at high concentrations of Pipes greatly exceeded that at low concentrations. With Mes, equivalent turbidity developed at both high and low buffer concentrations. Although associated proteins copolymerized with tubulin at low buffer concentrations, they were excluded from the polymerized material at high buffer concentrations. Pipes and Mes were compared to sodium phosphate, Tris/HCl and imidazole/HCl buffers at 0.1 M in several polymerization systems using both purified tubulin and microtubule protein. The sulfonate buffers were invariably associated with more vigorous reactions than the other buffers.

Alkanesulfonates↗
PubMed1988

Characterization of an inhibitor of actin polymerization in vinculin-rich fraction of turkey gizzard smooth muscle.

We report here on the purification and characterization of a new 25-kDa inhibitor of actin polymerization from turkey gizzard smooth muscle. The protein was purified by chromatography on DEAE-cellulose and hydroxyapatite, as well as by affinity chromatography on an immobilized-antibody column. The purified polypeptide reduced the low-shear viscosity of actin, apparently due to its inhibitory effect on actin polymerization. We demonstrate that this protein is largely responsible for the apparent inhibitory activity previously reported to be associated with smooth muscle vinculin preparations. Three independent monoclonal antibodies prepared against the 25-kDa inhibitor of actin polymerization can effectively adsorb the inhibiting activity of actin polymerization from the crude vinculin preparation or inhibit it. We also show here that the 25-kDa inhibitor of actin polymerization tends to undergo dimerization when maintained in non-reducing buffers, concomitant with the loss of its inhibitory activity. Immunohistochemical labeling of frozen sections, as well as immunoblotting analyzes, indicated that the 25-kDa inhibitor of actin polymerization is particularly enriched in smooth muscle cells and that its distribution is apparently homogenous throughout the cytoplasm showing no apparent enrichment in the vinculin-rich dense plaques located along the endofacial surface of the plasma membrane.

Actins↗
PubMed2000

Effect of ramped light intensity on polymerization force and conversion in a photoactivated composite.

PURPOSE: This study evaluated the effect of ramped light intensity on the polymerization shrinkage forces and degrees of conversion (DC) of a hybrid composite. MATERIALS AND METHODS: Composite samples were bonded between two steel rods (2.50 mm diameter, 1.25 mm apart, configuration factor = 1.0) mounted in a universal testing machine using a constant displacement mode. Polymerization contraction force was recorded for 250 seconds under four light exposure conditions: group 1, STD: (40 s x 800 mW/cm2); group 2, EXP: (150 mW/cm2 logarithmic increase to 800 mW/cm2 over 15 s) + (25 s x 800 mW/cm2); group 3, 2-STEP: (10 s x 150 mW/cm2) + (30 s x 800 mW/cm2); group 4, MED: (80 s x 400 mW/cm2). Maximum curing force (N250s) and maximum force rate of the four groups were compared using one-way analysis of variance (ANOVA) (alpha = 0.05) and the Tukey test. Degrees of conversion obtained with STD, EXP, and MED cure modes were evaluated at three depths (top surface, 1 mm, and 2 mm) using Fourier transform infrared spectroscopy (FTIR). RESULTS: Maximum rates of polymerization shrinkage force development and standard deviations (SD), in ascending order, were group 4, MED: 0.33 +/- 0.03 N/s; group 2, EXP: 0.35 +/- 0.06 N/s; group 1, STD: 0.44 +/- 0.03 N/s; and group 3, 2-STEP: 0.46 +/- 0.07 N/s. Maximum rates of polymerization shrinkage force development of group 2, EXP and group 4, MED were statistically equivalent and lower than those of group 1, STD and group 3, 2-STEP. Maximum shrinkage forces (+/- SD), in ascending order, were group 2, EXP: 20.4 +/- 2.5 N; group 4, MED: 25.8 +/- 1.0 N; group 3, 2-STEP: 27.4 +/- 5.8 N, and group 1, STD: 30.5 +/- 2.7 N. Maximum force of the EXP mode was statistically lower than MED, 2-STEP, and STD curing modes. The EXP ramp was successful in reducing the conversion rate at the top surface and at 1.0-mm depth, but it did not affect the total conversion compared to the STD 40-second cure mode. There was no difference in DC at the top surface and 1-mm depth with mode of cure. The MED cure mode resulted in a higher DC than the EXP mode at a depth of 2 mm. CLINICAL SIGNIFICANCE: Maximum shrinkage force and force rate exhibited during the first 250 seconds of polymerization were significantly lower using a ramped light intensity exposure. Ramped light intensity decreased conversion rate at the top surface and at 1.0-mm depth and did not affect the total extent of conversion compared to a standard 40-second, single-intensity cure mode. The slower conversion rate resulting from ramped light intensity helped to reduce the rate and maximum polymerization stress, but would not be expected to compromise the physical properties for the restorative material, since similar degrees of conversion were obtained.

Analysis of Variance↗
PubMed2002

Dielectric in situ monitoring of microgravity polymerizations.

The objective of the research described here is to develop dielectric spectroscopy to monitor polymerization reactions and processes in microgravity. Ground based measurements have been made on both neat thermoset resins and solution polymerization reactions. Polymerization of diglycidyl ether of bisphenol A (DGEBA) using two curing agents, m-phenylenediamine (m-PDA), and 4,4'-diamino-diphenyl-methane (DDM) were investigated to determine the relationship between the dielectric spectra and the thermoset polymer network and morphology. The results for the epoxy thermosets indicate that this technique can be used to monitor the extent of polymerization and the qualitative nature of polymer network. The photopolymerization of 6-(2-methyl-4-nitroanilino)-2,4-hexadiyn-1-ol (DAMNA) in solution was also investigated to determine if gravitational effects could be observed using dielectric spectroscopy. The technique is able to distinguish between surface and solution polymerizations during formation of the polydiacetylene thin films. In addition, it is capable of monitoring convective effects during solution polymerization.

Journal Article↗
PubMed1996

Polymers with Very Low Polydispersities from Atom Transfer Radical Polymerization

A radical polymerization process that yields well-defined polymers normally obtained only through anionic polymerizations is reported. Atom transfer radical polymerizations of styrene were conducted with several solubilizing ligands for the copper(I) halides: 4,4'-di-tert-butyl, 4,4'-di-n-heptyl, and 4,4'-di-(5-nonyl)-2,2'-dipyridyl. The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities (ratio of the weight-average to number-average molecular weights of 1.04 to 1.05). Similar results were obtained for the polymerization of acrylates.

Journal Article↗
PubMed1996

Prolonged and preferential production of polymeric immunoglobulin A in response to Streptococcus pneumoniae capsular polysaccharides.

Streptococcus pneumoniae is an invasive mucosal pathogen for which host defense is dependent on capsular polysaccharide-specific antibody. Capsule-specific immunoglobulin G (IgG), IgM, and IgA are produced following pneumococcal vaccination and infection. Serum IgA has two molecular forms, polymeric and monomeric. These forms may modulate the avidity of antigen binding and evolve over time as the immune response matures. Therefore, we sequentially characterized the molecular forms of serum IgA to three serotypes of pneumococcal capsular polysaccharides (types 8, 12F, and 14) after pneumococcal vaccination and after natural infection with type 14 S. pneumoniae. Although typically the form of IgA in antigen-specific systemic responses to protein antigens is predominantly polymeric in sera of patients shortly after exposure and shifts to the monomeric form in sera obtained several weeks later, the form of IgA in response to each pneumococcal capsular polysaccharide remained predominantly polymeric 1 month after natural infection and up to I year following vaccination. In contrast, IgA to pneumococcal cell wall polysaccharide was both polymeric and monomeric. Moreover, the form of IgA in response to polyribosyl-ribitol-phosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b, was predominantly monomeric in the sera of 8 of 10 subjects tested 1 to 3 months after vaccination with either PRP alone or the diphtheria toxoid conjugate of PRP. We conclude that systemic responses to pneumococcal capsular polysaccharides are distinct in the production of predominantly polymeric IgA over time. The persistence of polymeric IgA may facilitate binding and clearance of pneumococci from the systemic circulation or reflect limited maturation of the immune response to pneumococcal capsular polysaccharides.

Adult↗
PubMed1987

Kinetics of anti-Campylobacter jejuni monomeric and polymeric immunoglobulin A1 and A2 responses in serum during acute enteritis.

The intensity and kinetics of the serum polymeric and monomeric immunoglobulin A1 (IgA1) and IgA2 antibody responses to Campylobacter jejuni were analyzed. A rapid and marked serum IgA antibody response involving both the monomeric and polymeric components of IgA was observed after C. jejuni infections. IgA antibodies reached a peak of activity in serum during week 2 after the first symptoms of enteritis, about 10 days before the peak of IgG activity. Polymeric IgA accounted for most of the anti-C. jejuni activity at the peak of the IgA response (median, 90%; range, 44 to 98%) but rapidly disappeared from serum over a few weeks. In contrast, the serum monomeric IgA antibody response was low and was maintained over a prolonged period of time. Anti-C. jejuni IgA detected in the serum of healthy blood donors was mainly monomeric (median, 83%; range, 17 to 94%). In both the patients and the positive controls, IgA1 was the predominant (greater than 85%) subclass involved, even when the IgA antibody response was mainly polymeric. Our results suggest that polymeric IgA antibody responses are linked to a strong or persisting antigenic stimulation or both. Polymeric IgA antibodies appear to be a potential marker of acute C. jejuni infections, and their determination could provide a useful tool for the serological diagnosis of recent C. jejuni infections.

Acute Disease↗
PubMed2005

Effects of chronic portal hypertension on agonist-induced actin polymerization in small mesenteric arteries.

The ability of arterial smooth muscle to respond to vasoconstrictor stimuli is reduced in chronic portal hypertension (PHT). Additional evidence supports the existence of a postreceptor defect in vascular smooth muscle excitation contraction coupling. However, the nature of this defect is unclear. Recent studies have shown that vasoconstrictor stimuli induce actin polymerization in smooth muscle and that the associated increase in F-actin is necessary for force development. In the present study we have tested the hypothesis that impaired actin polymerization contributes to reduced vasoconstrictor function in small mesenteric arteries derived from rats with chronic prehepatic PHT. In vitro studies were conducted on small mesenteric artery vessel rings isolated from normal and PHT rats. Isometric tension responses to incremental concentrations of phenylephrine were significantly reduced in PHT arteries. The ability to polymerize actin in portal hypertensive mesenteric arteries stimulated by phenylephrine was attenuated compared with control. Inhibition of cAMP-dependent protein kinase (PKA) restored agonist-induced actin polymerization of arteries from PHT rats to normal levels. Depolymerization of actin in arteries from normal rats reduced maximal contractile force but not myosin phosphorylation, suggesting a key role for the dynamic regulation of actin polymerization in the maintenance of vascular smooth muscle contraction. We conclude that reductions in agonist-induced maximal force development of PHT vascular smooth muscle is due, in part, to impaired actin polymerization, and prolonged PKA activation may underlie these changes.

Actin Cytoskeleton↗
PubMed2002

Kinetics and hydrolysis mechanism of polymeric prodrugs containing ibuprofen, ketoprofen, and naproxen as pendent agents.

Polymeric prodrugs were prepared using methacrylic acid (MA) copolymerization with 2-hydroxyethyl methacrylate (HEMA), covalently linked with ibuprofen (HI), ketoprofen (HK), or naproxen (HN). It was previously shown that the acceptable composition of drug-linked monomer in polymeric prodrugs to prevent gastric mucosa irritation and maintain water solubility was in the range of 20-40 mol%. To investigate the applicability of these polymeric prodrugs, hydrolysis rates of HK-25, HN-29, and HI-30 (the number indicates the mole percent of the drug-linked monomers in the polymeric prodrugs), were studied in vitro with or without esterase. The polymeric prodrugs released a major fraction of the parent drugs and a fraction of the hydroxyethyl ester drug derivatives (drug-EtOH). The calculated hydrolysis rate constants and results correlated to the drug structural solubility and steric hindrance are discussed. The anti-inflammatory properties of these polymeric prodrugs were evaluated using carrageenan-induced edema test. The results indicate that HK-25 and HN-29 display greater potency to inhibit acute inflammatory processes than the free drugs over long periods. HI-30, however, retains a potency comparable to that of free ibuprofen.

Animals↗
PubMed2004

Controlled synthesis of biodegradable lactide polymers and copolymers using novel in situ generated or single-site stereoselective polymerization initiators.

Polylactides and their copolymers are key biodegradable polymers used widely in biomedical, pharmaceutical and ecological applications. The development of synthetic pathways and catalyst/initiator systems to produce pre-designed polylactides, as well as the fundamental understanding of the polymerization reactions, has continuously been an important topic. Here, we will address the recent advances in the ring-opening polymerization of lactides, with an emphasis on the highly versatile in situ generated initiator systems and single-site stereoselective initiators. The in situ generated initiators including in situ formed yttrium, calcium and zinc alkoxides all have been shown to bring about a rapid and living polymerization of lactides under mild conditions, which facilitated the preparation of a variety of advanced lactide-based biomaterials. For example, well-defined di- and tri-block copolymers consisting of hydrophilic poly(ethylene glycol) blocks and hydrophobic polyester blocks, which form novel biodegradable polymersomes or biodegradable thermosensitive hydrogels, have been prepared. In the past few years, significant progress has also been made in the area of stereoselective polymerization of lactides. This new generation of initiators has enabled the production of polylactide materials with novel microstructures and/or properties, such as heterotactic (--RRSSRRSSRRSS--) polylactide, crystalline syndiotactic (--RSRSRSRSRSRS--) polylactide and isotactic stereoblock (--Rn Sn Rn Sn--) polylactide, exhibiting a high melting temperature. The recently developed polymerizations using in situ generated initiators and stereoselective polymerizations have no doubt opened a brand-new avenue for the design and exploration of polylactides and their copolymers.

Biocompatible Materials↗
PubMedDate not supplied

Acute effects of continuous nasogastric tube feeding on gastric function: comparison of a polymeric and a nonpolymeric formula.

The acute effects of continuous intragastric administration of 1500 ml (4200 kJ/liter) of a polymeric and of a nonpolymeric formula on gastric function were studied in 15 healthy subjects. During 450 min 1500 ml, containing 6300 kJ (1500 kcal), was given through a nasogastric tube. At regular intervals the volume, the pH, the titratable acidity, and the pepsin activity of the gastric contents and the plasma gastrin concentration were determined. Maximal observed intragastric volumes occurred after 120 min (118 +/- 16 ml during polymeric formula, 212 +/- 37 ml during nonpolymeric one) and volumes subsequently halved (at 450 min 68 +/- 13 and 104 +/- 16 ml, respectively). During the administration of both polymeric and the nonpolymeric formula intragastric pH fell progressively to 3.15 and 2.67, respectively, at 450 min. Incremental plasma gastrin values increased between 120 and 450 min from 7 to 12 ng/liter during the polymeric formula. During the nonpolymeric one it stabilized after 120 min at 12 ng/liter. When the whole test periods were considered integrated, mean intragastric volumes tended to be larger during the nonpolymeric formula (153 +/- 23 ml) than during the polymeric formula (107 +/- 12 ml), but this difference was not statistically significant. Median integrated mean pH was lower during the nonpolymeric formula (2.89) compared with the polymeric one (3.26). Despite the limitation that the investigations were performed in healthy subjects only, it is concluded from this study that the risk of aspiration during continuous nasogastric tube feeding is probably greatest during the first few hours of administration because of the larger intragastric volumes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Substitution of the gamma-chain Asn308 disturbs the D:D interface affecting fibrin polymerization, fibrinopeptide B release, and FXIIIa-catalyzed cross-linking.

Crystallographic structures indicate that gamma-chain residue Asn308 participates in D:D interactions and indeed substitutions of gammaAsn308 with lysine or isoleucine have been identified in dysfibrinogens with impaired polymerization. To probe the role of Asn308 in polymerization, we synthesized 3 variant fibrinogens: gammaAsn308 changed to lysine (gammaN308K), isoleucine (gammaN308I), and alanine (gammaN308A). We measured thrombin-catalyzed polymerization by turbidity, fibrinopeptide release by high-performance liquid chromatography, and factor XIIIa-catalyzed cross-linking by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the absence of added calcium, polymerization was clearly impaired with all 3 variants. In contrast, at 0.1 mM calcium, only polymerization of gammaN308K remained markedly abnormal. The release of thrombin-catalyzed fibrinopeptide B (FpB) was delayed in the absence of calcium, whereas at 1 mM calcium FpB release was delayed only with gammaN308K. Factor XIIIa-catalyzed gamma-gamma dimer formation was delayed with fibrinogen (in absence of thrombin), whereas with fibrin (in presence of thrombin) gamma-gamma dimer formation of only gammaN308K was delayed. These data corroborate the recognized link between FpB release and polymerization. They show fibrin cross-link formation likely depends on the structure of protofibrils. Together, our results show substitution of Asn308 with a hydrophobic residue altered neither polymer formation nor polymer structure at physiologic calcium concentrations, whereas substitution with lysine altered both.

Amino Acid Substitution↗
PubMed2005

Fibrinogen Philadelphia, a hypodysfibrinogenemia characterized by abnormal polymerization and fibrinogen hypercatabolism due to gamma S378P mutation.

Fibrinogen Philadelphia, a hypodysfibrinogenemia described in a family with a history of bleeding, is characterized by prolonged thrombin time, abnormal fibrin polymerization, and increased catabolism of the abnormal fibrinogen. Turbidity studies of polymerization of purified fibrinogen under different ionic conditions reveal a reduced lag period and lower final turbidity, indicating more rapid initial polymerization and impaired lateral aggregation. Consistent with this, scanning and transmission electron microscopy show fibers with substantially lower average fiber diameters. DNA sequence analysis of the fibrinogen genes A, B, and G revealed a T>C transition in exon 9 resulting in a serine-to-proline substitution near the gamma chain C-terminus (S378P). The S378P mutation is associated with fibrinogen Philadelphia in this kindred and was not found in 10 controls. This region of the gamma chain is involved in fibrin polymerization, supporting this as the polymerization defect causing the mutation. Thus, this abnormal fibrinogen is characterized by 2 unique features: (1) abnormal polymerization probably due to a major defect in lateral aggregation and (2) hypercatabolism of the mutant protein. The location, nature, and unusual characteristics of this mutation may add to our understanding of fibrinogen protein interactions necessary for normal catabolism and fibrin formation.

Afibrinogenemia↗
PubMed2002

Arp2/3 complex is required for actin polymerization during platelet shape change.

Platelets undergo a series of actin-dependent morphologic changes when activated by thrombin receptor activating peptide (TRAP) or when spreading on glass. Polymerization of actin results in the sequential formation of filopodia, lamellipodia, and stress fibers, but the molecular mechanisms regulating this polymerization are unknown. The Arp2/3 complex nucleates actin polymerization in vitro and could perform this function inside cells as well. To test whether Arp2/3 regulated platelet actin polymerization, we used recombinant Arp2 protein (rArp2) to generate Arp2-specific antibodies (alpha Arp2). Intact and Fab fragments of alpha Arp2 inhibited TRAP-stimulated actin-polymerizing activity in platelet extracts as measured by the pyrene assay. Inhibition was reversed by the addition of rArp2 protein. To test the effect of Arp2/3 inhibition on the formation of specific actin structures, we designed a new method to permeabilize resting platelets while preserving their ability to adhere and to form filopodia and lamellipodia on exposure to glass. Inhibition of Arp2/3 froze platelets at the rounded, early stage of activation, before the formation of filopodia and lamellipodia. By morphometric analysis, the proportion of platelets in the rounded stage rose from 2.85% in untreated to 63% after treatment with alpha Arp2. This effect was also seen with Fab fragments and was reversed by the addition of rArp2 protein. By immunofluorescence of platelets at various stages of spreading, the Arp2/3 complex was found in filopodia and lamellipodia. These results suggest that activation of the Arp2/3 complex at the cortex by TRAP stimulation initiates an explosive polymerization of actin filaments that is required for all subsequent actin-dependent events.

Actin Cytoskeleton↗
PubMed1985

Progesterone withdrawal stimulates mammary gland tubulin polymerization in pregnant rats.

The size of the polymerized tubulin pool in mammary glands of late pregnant rats increased 2.4-fold 24 h after bilateral ovariectomy using a [3H]colchicine binding assay for tubulin. The total (free plus polymerized) tubulin concentration was not altered. Stimulation of tubulin polymerization as well as the induced rise in lactose content were both completely inhibited in rats that had been fitted with progesterone implants at the time of surgery. The increase in polymerized tubulin was not blocked by 17 beta-estradiol implants, although this treatment did partially inhibit the rise in tissue lactose following ovariectomy. The results indicate that increased polymerization during induced lactogenesis reflects a shift of free tubulin into the polymerized pool and that this shift is related to the withdrawal of progesterone.

Animals↗
PubMed1998

Chromatin binding and polymerization of the endogenous Xenopus egg lamins: the opposing effects of glycogen and ATP.

We have previously identified and quantitated three B-type lamin isoforms present in the nuclei of mature Xenopus laevis oocytes, and in cell-free egg extracts. As Xenopus egg extracts are frequently used to analyze nuclear envelope assembly and lamina functions, we felt it was imperative that the polymerization and chromatin-binding properties of the endogenous B-type egg lamins be investigated. While we have demonstrated that soluble B-type lamins bind to chromatin, we have also observed that the polymerization of egg lamins does not require membranes or chromatin. Lamin assembly is enhanced by the addition of glycogen/glucose, or by the depletion of ATP from the extract. Moreover, the polymerization of egg cytosol lamins and their binding to demembranated sperm or chromatin assembled from naked lambda-DNA is inhibited by an ATP regeneration system. These ATP-dependent inhibitory activities can be overcome by the coaddition of glycogen to egg cytosol. We have observed that glycogen does not alter ATP levels during cytosol incubation, but rather, as glycogen-enhanced lamin polymerization is inhibited by okadaic acid, we conclude that glycogen activates protein phosphatases. Because protein phosphatase 1 (PP1) is the only phosphatase known to be specifically regulated by glycogen our data indicate that PP1 is involved in lamin polymerization. Our results show that ATP and glycogen effect lamin polymerization and chromatin binding by separate and opposing mechanisms.

Adenosine Triphosphate↗