scholarly journals Structural and dynamic states of actin in the erythrocyte

1983 ◽  
Vol 96 (3) ◽  
pp. 768-775 ◽  
Author(s):  
JC Pinder ◽  
WB Gratzer
Keyword(s):  
Guanidine Hydrochloride ◽  
Monomer Concentration ◽  
Degree Of Polymerization ◽  
Actin Monomer ◽  
Measured Concentration ◽  
Whole Cells ◽  
Cytoskeletal Network ◽  
Cytochalasin E ◽  
Oligomeric Complex ◽  
Low Ionic Strength

Analysis of the nucleotide tightly associated with isolated erythrocyte cytoskeletons show it to be ADP, rather then ATP. This confirms that at least a major part of the erythrocyte actin is in the F-form. A re-evaluation of the stoichiometry of spectrin and actin in the erythrocyte (taking account of a gross difference between the color responses of the two proteins on staining of electrophoretic gels) leads to values of 1x10(5) and 5x10(5) for the number of molecules of spectrin tetramer and actin respectively per cell. It has been found possible to perform spectrophotometric DNAase I assays fro actin on lysed whole cells. The concentration of monomeric actin at 0 degrees C is approximately 16 μg/ml packed cells. After washing the lysed cells the monomer pool is not re-established, indicating that only a small proportion of the actin subunits are free to dissociate. The actin monomer concentration in the cytosol remains unchanged after equilibration of the cells with cytochalasin E. The ability of actin-containing complexes in the membrane to nucleate the polymerization of added G-actin was measured fluorimetrically; it was found that membranes incubated with cytochalasin E were completely inert with respect to nucleating activity under conditions that favor appreciable growth at the slowly-growing ("pointed") ends of free actin filaments. This suggests that these ends of the actin "protofilaments" in the red cell are blocked or sterically obstructed. After treatment of the membranes with guanidine hydrochloride under conditions that dissociate F-actin, the measured concentration of actin monomer rises to approximately 180 μg/ml of packed cells, which is nearly 70 percent of the total actin content. On treatment with trypsin in the presence of DNAase, the spectrin and 4.1 are extensively degraded, but the actin remains undamaged. This treatment, followed by exposure to guanidine hydrochloride, causes a further rise in the concentration of actin responsive to the DNAase assay to 250 μg/ml of cells, compared with 270 μg/ml estimated by densitometry of stained gels. The oligomeric complex, consisting of actin, spectrin, and 4.1, that is extracted from the membrane at low ionic strength, generates no detectable actin monomer after the same treatment. From literature data on the number of cytochalasin binding sites per cell and our value for the total actin content, we obtain a number-average degree of polymerization for actin in the membrane of 12-17. The results lead to a model for the structure of the cytoskeletal network and suggest some consequences of metabolic depletion.

scholarly journals Mechanical Characterization of a Dynamic and Tunable Methacrylated Hyaluronic Acid Hydrogel

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Matthew G. Ondeck ◽  
Adam J. Engler
Keyword(s):  
Hyaluronic Acid ◽  
Elastic Modulus ◽  
Monomer Concentration ◽  
Degree Of Polymerization ◽  
Force Microscopy ◽  
3T3 Fibroblasts ◽  
Atomic Force ◽  
Spread Area ◽  
Nih 3T3

Hyaluronic acid (HA) is a commonly used natural polymer for cell scaffolding. Modification by methacrylate allows it to be polymerized by free radicals via addition of an initiator, e.g., light-sensitive Irgacure, to form a methacrylated hyaluronic acid (MeHA) hydrogel. Light-activated crosslinking can be used to control the degree of polymerization, and sequential polymerization steps allow cells plated onto or in the hydrogel to initially feel a soft and then a stiff matrix. Here, the elastic modulus of MeHA hydrogels was systematically analyzed by atomic force microscopy (AFM) for a number of variables including duration of UV exposure, monomer concentration, and methacrylate functionalization. To determine how cells would respond to a specific two-step polymerization, NIH 3T3 fibroblasts were cultured on the stiffening MeHA hydrogels and found to reorganize their cytoskeleton and spread area upon hydrogel stiffening, consistent with cells originally cultured on substrates of the final elastic modulus.

scholarly journals Cytochalasins inhibit nuclei-induced actin polymerization by blocking filament elongation.

1980 ◽  
Vol 84 (2) ◽  
pp. 455-460 ◽  
Author(s):  
D C Lin ◽  
K D Tobin ◽  
M Grumet ◽  
S Lin
Keyword(s):  
Binding Sites ◽  
Actin Polymerization ◽  
Cytochalasin B ◽  
Molecular Size ◽  
Muscle Actin ◽  
Competitive Displacement ◽  
Low Concentrations ◽  
Relative Affinity ◽  
Cytochalasin E ◽  
Low Ionic Strength

Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer containing 0.4 mM MgCl2. The rate of induced polymerization was dependent on the amount and on the molecular size of the polylysine added. A similar effect was obtained by adding actin nuclei (containing about 2-4 actin subunits) cross-linked by p-N,N'-phenylenebismaleimide to G-actin under the same conditions, suggesting that the effect of polylysine is due to promotion of the formation of actin nuclei. Polymerization induced by polylysine and by cross-linked actin nuclei was inhibited by low concentrations (10(-8)-10(-6)M) of cytochalasins. Binding experiments showed that actin filaments, but not actin monomers, contained high-affinity binding sites for [3H]cytochalasin B (one site per 600 actin monomers). The relative affinity of several cytochalasins for these sites (determined by competitive displacement of [3H]dihydrocytochalasin B) was: cytochalasin D greater than cytochalasin E approximately equal to dihydrocytochalasin B. The results of this study suggest that cytochalasins inhibit nuclei-induced actin polymerization by binding to highly specific sites at the point of monomer addition, i.e., the elongation site, in actin nuclei and filaments.

Evidence for a membrane-bound form of a bacteriocin of Bacteroides uniformis Tl-1

1984 ◽  
Vol 30 (2) ◽  
pp. 268-272 ◽  
Author(s):  
Sandra L. Austin-Prather ◽  
S. James Booth
Keyword(s):  
Molecular Weight ◽  
Outer Surface ◽  
Guanidine Hydrochloride ◽  
Membrane Vesicles ◽  
Apparent Molecular Weight ◽  
Whole Cells ◽  
Membrane Bound ◽  
Bleb Formation

The bacteriocin of Bacteroides uniformis Tl-1 had previously been reported to have a molecular weight of ≥ 300 000. Reexamination of the B. uniformis bacteriocin revealed that the bacteriocin was found in association with membrane vesicles which had been released by bleb formation from the outer surface of the B. uniformis cells. The bacteriocin could be released from whole cells or purified membrane vesicles by treatment with 6 M guanidine hydrochloride or 7 M urea and had an apparent molecular weight of 5000–6200.

Studies on microcapsules. VI. Effect of variations in polymerization condition on microcapsule size

1970 ◽  
Vol 48 (13) ◽  
pp. 2047-2051 ◽  
Author(s):  
Yoshimichi Shigeri ◽  
Masumi Koishi ◽  
Tamotsu Kondo ◽  
Motoharu Shiba ◽  
Suiichi Tomioka
Keyword(s):  
Monomer Concentration ◽  
Degree Of Polymerization ◽  
Interfacial Polycondensation ◽  
Polymerization Condition

The effect of variations in polymerization condition on the size of microcapsules prepared by the interfacial polycondensation method was studied. Factors lowering the rate and degree of polymerization, such as a decrease in temperature or monomer concentration, were found to increase the microcapsule size. A mechanism was proposed for the formation of large microcapsules in the polycondensation step.

The polymerization of styrene by sulphuric acid - I. Theory of fast-initiated non-stationary polymerization

1961 ◽  
Vol 263 (1312) ◽  
pp. 58-62 ◽  
Keyword(s):  
Sulphuric Acid ◽  
Time Course ◽  
Monomer Concentration ◽  
Degree Of Polymerization ◽  
Average Degree ◽  
Chain Reaction ◽  
First Order ◽  
Chain Lengths ◽  
Special Case ◽  
Termination Process

Theoretical relationships are derived for the time course, yield, and number-average degree of polymerization in a non-stationary chain reaction having a very rapid initiation process and a first-order termination process. The distribution of chain lengths is derived for the special case of constant monomer concentration.

scholarly journals Thiol-dependent changes in the properties of rat liver sulphotransferases

1971 ◽  
Vol 123 (3) ◽  
pp. 427-434 ◽  
Author(s):  
D. J. Barford ◽  
J. G. Jones
Keyword(s):  
Ionic Strength ◽  
Methyl Ester ◽  
Molecular Size ◽  
Degree Of Polymerization ◽  
Prolonged Storage ◽  
Kinetic Properties ◽  
Female Rat ◽  
Km Value ◽  
Low Ionic Strength ◽  
Rat Livers

1. Two enzymes (A and B) which catalyse the sulphation of p-nitrophenol and l-tyrosine methyl ester have been isolated from female rat livers. One of these enzymes (A) also catalyses the sulphation of dehydroepiandrosterone. 2. The Km values for the sulphation of p-nitrophenol and l-tyrosine methyl ester by enzyme B at pH7.5 are 1.5μm and 2.9mm respectively. 3. Enzyme B is oxidized on keeping at 0°C when the Km and Vmax. values for the sulphation of p-nitrophenol are increased approx. 200-fold and fourfold respectively. This oxidized preparation of enzyme B fails to catalyse the sulphation of l-tyrosine methyl ester. 4. When the oxidized form of enzyme B is kept at 0°C and low ionic strength then further forms of p-nitrophenol sulphotransferase are produced having even lower affinities for the sulphate acceptor. 5. The Km value for adenosine 3′-phosphate 5′[35S]-sulphatophosphate is not affected during storage of the enzyme under these conditions. 6. Prolonged storage of enzyme B at low ionic strength leads to a considerable degree of polymerization of p-nitrophenol sulphotransferase and l-tyrosine methyl ester sulphotransferase. 7. The changes in the kinetic properties and molecular size of enzyme B during storage are reversed by dithiothreitol.

scholarly journals Reactivation of triosephosphate isomerase from three trypanosomatids and human: effect of Suramin

1998 ◽  
Vol 332 (1) ◽  
pp. 91-96 ◽  
Author(s):  
Xiu-Gong GAO ◽  
Georgina GARZA-RAMOS ◽  
Emma SAAVEDRA-LIRA ◽  
Nallely CABRERA ◽  
Marietta T. de GÓMEZ-PUYOU ◽  
...  
Keyword(s):  
Protein Concentration ◽  
Triosephosphate Isomerase ◽  
Guanidine Hydrochloride ◽  
Monomer Concentration ◽  
Life Time ◽  
The Other ◽  
Drug Of Choice ◽  
Rate Limiting Step ◽  
Order Of Magnitude ◽  
Rate Limiting

The reactivation of the homodimeric triosephosphate isomerases (TIMs) from Trypanosoma brucei, T. cruzi, Leishmania mexicana and humans was determined after their denaturation with guanidine hydrochloride. In the range of 2–32 µg of T. brucei TIM per ml and 0.2–5 µg of the other enzymes per ml, the rate and extent of TIM reactivation depended on protein concentration, indicating that at these protein concentrations, the rate-limiting step of reactivation is monomer association and not monomer folding. The rate of monomer association was more than one order of magnitude lower in the T. brucei enzyme than in the other three enzymes. Suramin is a drug of choice in the treatment of sleeping sickness, but its mechanism of action is not known. At micromolar concentrations, Suramin inhibited the reactivation of the four enzymes, but the extent of inhibition by Suramin decreased with increasing protein concentration as consequence of a diminution of the life time of the folded monomer. Since the life time of the monomer of T. brucei TIM is longer than that of the other enzymes, Suramin is a more effective inhibitor of the reactivation of TIM from T. brucei, particularly at monomer concentrations above 1 µg of protein per ml (monomer concentration approx. 37 nM). Compounds that are structurally related to Suramin also inhibit TIM reactivation; their effect was about five times more pronounced in the enzyme from T. brucei than in human TIM.

Nonlinear increase of elongation rate of actin filaments with actin monomer concentration

Biochemistry ◽  
1986 ◽  
Vol 25 (17) ◽  
pp. 4899-4906 ◽  
Author(s):  
Thomas Keiser ◽  
Achim Schiller ◽  
Albrecht Wegner
Keyword(s):  
Actin Filaments ◽  
Monomer Concentration ◽  
Elongation Rate ◽  
Actin Monomer ◽  
Nonlinear Increase

Radio-iodide uptake by modified poly (glycidyl methacrylate) as anion exchange resin

2017 ◽  
Vol 105 (1) ◽  
Author(s):  
Sameh H. Othman ◽  
Ahmed M. Elbarbary ◽  
Ghada Rashad ◽  
T. W. Fasih
Keyword(s):  
Anion Exchange ◽  
Glycidyl Methacrylate ◽  
Exchange Resin ◽  
Anion Exchange Resin ◽  
Epoxy Group ◽  
Monomer Concentration ◽  
Absorbed Dose ◽  
Degree Of Polymerization ◽  
Iodide Uptake ◽  
Factors Affecting

AbstractPoly(glycidyl methacrylate) (PGMA) microspheres were prepared by radiation induced polymerization of glycidyl methacrylate (GMA) monomer. The factors affecting the degree of polymerization and yield (%) of PGMA such as type of solvent, monomer concentration, and irradiation dose were investigated. It was found that the PGMA yield (%) increases with increasing monomer concentration up to 50% and absorbed dose of 5 kGy. The resulting PGMA containing the epoxy group waschemically modified by hydroxyl amine to act as anion-exchange resin for uptake of

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