Ultrastructural Kinetics of Electrically Induced Fusion of Human Erythrocytes

1985 ◽  
Vol 43 ◽  
pp. 494-495
Author(s):  
D.A. Stenger
Keyword(s):  
Electrical Breakdown ◽  
Freeze Fracture ◽  
Kinetic Mechanism ◽  
Eukaryotic Cell ◽  
Copper Sample ◽  
Human Erythrocytes ◽  
Flux Lines ◽  
Latex Beads ◽  
Electric Flux ◽  
Kinetics Of

Conditions for electrical breakdown and subsequent fusion of biological membranes have been reported for a variety of eukaryotic cell systems. Large fusion yields may be obtained by first causing cells to form pearl chains parallel to the electric flux lines in a high frequency a.c. field by a process known as dielectrophoresis. The dielectrophoretic force affords close positioning of the cells and facilitates maintenance and expansion of intercellular membrane and cytoplasmic contiguity initiated by one or more sharp square pulses directed through the pearl chains. Reversible disruption of the cell membrane occurs when the compressive electrical force caused by the square pulse exceeds a critical value.This investigation focused on elucidating the ultrastructural kinetic mechanism(s) involved in the electrically-induced fusion of human erythrocytes. In this case, rapid freeze copper sample holders for freeze-fracture were incorporated as electrodes into a circuit capable of performing the type of protocol described above (Fig. 1). Washed human erythrocytes were suspended in 0.3 M sucrose containing 25.7 μm latex beads for electrode separation.

Video-microscopic measurement of cell-substratum traction forces generated by locomoting keratocytes

1993 ◽  
Vol 51 ◽  
pp. 188-189
Author(s):  
Tim Oliver ◽  
Michelle Leonard ◽  
Juliet Lee ◽  
Akira Ishihara ◽  
Ken Jacobson
Keyword(s):  
Silicone Rubber ◽  
Molecular Motors ◽  
Video Frame ◽  
Traction Forces ◽  
Cell Traction Forces ◽  
Latex Beads ◽  
Cell Traction ◽  
Local Cell ◽  
Microscopic Measurement ◽  
Kinetics Of

We are using video-enhanced light microscopy to investigate the pattern and magnitude of forces that fish keratocytes exert on flexible silicone rubber substrata. Our goal is a clearer understanding of the way molecular motors acting through the cytoskeleton co-ordinate their efforts into locomotion at cell velocities up to 1 μm/sec. Cell traction forces were previously observed as wrinkles(Fig.l) in strong silicone rubber films by Harris.(l) These forces are now measureable by two independant means.In the first of these assays, weakly crosslinked films are made, into which latex beads have been embedded.(Fig.2) These films report local cell-mediated traction forces as bead displacements in the plane of the film(Fig.3), which recover when the applied force is released. Calibrated flexible glass microneedles are then used to reproduce the translation of individual beads. We estimate the force required to distort these films to be 0.5 mdyne/μm of bead movement. Video-frame analysis of bead trajectories is providing data on the relative localisation, dissipation and kinetics of traction forces.

Oxidation of Olefins Representing Some Structural Units of GR-S

1952 ◽  
Vol 25 (1) ◽  
pp. 21-32 ◽  
Author(s):  
W. C. Warner ◽  
J. Reid Shelton
Keyword(s):  
Phenyl Group ◽  
Kinetic Mechanism ◽  
Oxidation Reactions ◽  
Chain Reaction ◽  
Instantaneous Rate ◽  
Initial Oxygen ◽  
Oxidation Of Olefins ◽  
A Minor ◽  
The Relationship ◽  
Kinetics Of

Abstract Three olefins were oxidized in the liquid phase with molecular oxygen to determine the kinetics of the oxidation reactions and the relationship to oxidation of rubber. The instantaneous rate of oxidation was found to be related to the analytically determined olefin and peroxide concentrations by the equation : Rate=k (unreacted olefin)(peroxide), where rate equals moles of oxygen per mole of original olefin per hour and the parentheses represent molarities. Presence of a phenyl group was found to affect k, but only in a minor way, indicating that the same fundamental kinetic mechanism applies in both aromatic and aliphatic olefins. The data are consistent with the general kinetic mechanism of Bolland involving oxygen attack at the alpha-methylenic group. However, it appears probable that initial oxygen attack can also occur at the double bond, resulting in the formation of a peroxide biradical, which may then react with other olefin molecules, initiating the usual chain reaction mechanism.

scholarly journals Determination of the steady-state turnover rates of the metabolically active pools of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate in human erythrocytes

1989 ◽  
Vol 259 (3) ◽  
pp. 893-896 ◽  
Author(s):  
C E King ◽  
P T Hawkins ◽  
L R Stephens ◽  
R H Michell
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Human Erythrocytes ◽  
Turnover Rates ◽  
Metabolic Fluxes ◽  
Metabolic Pool ◽  
Phosphatidylinositol 4 ◽  
Kinetics Of ◽  
Phosphate Groups

When intact human erythrocytes are incubated at metabolic steady state in a chloride-free medium containing [32P]Pi, there is rapid labelling of the gamma-phosphate of ATP, followed by a slower labelling of the monoester phosphate groups of phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] [King, Stephens, Hawkins, Guy & Michell (1987) Biochem. J. 244, 209-217]. We have analysed the early kinetics of the labelling of these phosphate groups, in order to determine: (a) the steady-state rates of the interconversions of phosphatidylinositol, PtdIns4P and PtdIns(4,5)P2; and (b) the fractions of the total cellular complement of PtdIns4P and PtdIns(4,5)P2 that participate in this steady-state turnover. The experimental data most closely fit a pattern of PtdIns4P and PtdIns(4,5)P2 turnover in which one-quarter of the total cellular complement of each lipid is in the metabolic pool that participates in rapid metabolic turnover, with rate constants of 0.028 min-1 for the interconversion of PtdIns and PtdIns4P, and of 0.010 min-1 for the PtdIns4P/PtdIns(4,5)P2 cycle. These rate constants represent metabolic fluxes of approx. 2.1 nmol of lipid/h per ml of packed erythrocytes between PtdIns and PtdIns4P and of approx. 5.7 nmol/h per ml of cells between PtdIns4P and PtdIns(4,5)P2.

scholarly journals Human erythrocytes adhering to schistosomula of Schistosoma mansoni lyse and fail to transfer membrane components to the parasite.

1985 ◽  
Vol 101 (1) ◽  
pp. 158-166 ◽  
Author(s):  
J P Caulfield ◽  
C M Cianci
Keyword(s):  
Schistosoma Mansoni ◽  
Erythrocyte Membrane ◽  
Plasma Membranes ◽  
Freeze Fracture ◽  
Human Erythrocytes ◽  
Transmission Microscopy ◽  
Carbocyanine Dyes ◽  
Host Membrane ◽  
Membrane Components ◽  
20 Nm

We studied the adherence of human erythrocytes to larvae of the intravascular parasite Schistosoma mansoni by transmission microscopy, freeze fracture, and fluorescence techniques. In addition, we used the adherent cells to investigate the problem of host antigen acquisition. Schistosomula were cultured for from 24 to 48 h after transformation in order to clear the remnants of the cercarial glycocalyx. In some cases, the worms were preincubated with wheat germ agglutinin to promote adherence of the erythrocytes. The results were similar with and without the lectin except that more cells attached to the lectin-coated parasites. Erythrocytes adhered within a few hours and, unlike neutrophils, did not fuse with the parasite. A layer of 10-20-nm electron dense material separated the outer leaflets of the tegumental and plasma membranes. In addition, many deformed and lysed cells were seen on the parasite surface. The ability of the worm to acquire erythrocyte membrane constituents was tested with carbocyanine dyes, fluorescein covalently conjugated to glycophorin, monoclonal antibodies against B and H blood group glycolipids, and rabbit alpha-human erythrocyte IgG. In summary, glycophorin, erythrocyte proteins, and glycolipids were not transferred to the parasite membrane within 48 h. Carbocyanine dyes were rapidly transferred to the parasite with or without lectin preincubation. Thus, the dye in the worm membrane came from both adherent and nonadherent cells. These studies suggest that, in the absence of membrane fusion, the parasite may acquire some lipid molecules similar in structure to host membrane glycolipids by simple transfer through the medium but that B and H glycolipids and erythrocyte membrane proteins are not transferred from adhering cells to the worm.

scholarly journals The calculation of transcript flux ratios reveals single regulatory mechanisms capable of activation and repression

2018 ◽  
Vol 115 (50) ◽  
pp. E11604-E11613 ◽  
Author(s):  
Eric A. Galburt
Keyword(s):  
Rate Constants ◽  
Flux Ratio ◽  
Stringent Response ◽  
Kinetic Mechanism ◽  
Regulation Of Transcription ◽  
Sequence Motifs ◽  
Response Factors ◽  
Initiation Rate ◽  
Dna Sequence Motifs ◽  
Kinetics Of

The regulation of transcription allows cells to adjust the rate of RNA polymerases (RNAPs) initiated in a promoter-specific manner. Classically, transcription factors are directed to a subset of promoters via the recognition of DNA sequence motifs. However, a unique class of regulators is recruited directly through interactions with RNAP. Surprisingly, these factors may still possess promoter specificity, and it has been postulated that the same kinetic mechanism leads to different regulatory outcomes depending on a promoter’s basal rate constants. However, mechanistic studies of regulation typically report factor activity in terms of changes in the thermodynamics or kinetics of individual steps or states while qualitatively linking these observations to measured changes in transcript production. Here, I present online calculators that allow for the direct testing of mechanistic hypotheses by calculating the steady-state transcript flux in the presence and absence of a factor as a function of initiation rate constants. By evaluating how the flux ratio of a single kinetic mechanism varies across promoter space, quantitative insights into the potential of a mechanism to generate promoter-specific regulatory outcomes are obtained. Using these calculations, I predict that the mycobacterial transcription factor CarD is capable of repression in addition to its known role as an activator of ribosomal genes. In addition, a modification of the mechanism of the stringent response factors DksA/guanosine 5′-diphosphate 3′-diphosphate (ppGpp) is proposed based on their ability to differentially regulate transcription across promoter space. Overall, I conclude that a multifaceted kinetic mechanism is a requirement for differential regulation by this class of factors.

Simulated growth and microstructure of DyBa2Cu3O7−x with and without Dy2BaCuO5 addition

1995 ◽  
Vol 10 (2) ◽  
pp. 268-273 ◽  
Author(s):  
N. Vandewalle ◽  
R. Cloots ◽  
M. Ausloos
Keyword(s):  
Growth Front ◽  
Kinetic Mechanism ◽  
Optical Observations ◽  
Kinetic Processes ◽  
Eden Model ◽  
Kinetics Of ◽  
Simulated Growth ◽  
Simple Models ◽  
Growth Probability

We present optical observations of magnetically melt-textured DyBa2Cu3O7−x with and without 20 wt. % excess of Dy2BaCuO5. From these observations, we propose some kinetic mechanism of the growth of 123 compounds. Kinetic processes can be simulated on computers. Two (very) simple models derived from the well-known Eden model are presented. They simulate the growth of the grain front. The simulated patterns agree with the observations. The microstructure of such materials cannot be explained by thermodynamic and chemical considerations alone, but explanations must include the kinetics of the growth front as well. From our observations, we conclude that the growth probability ratios g110/g100 and g100/g001 are of the order of 10 and 50, respectively.

Kinetics of uptake and deacetylation of N-acetylcysteine by human erythrocytes

2007 ◽  
Vol 39 (9) ◽  
pp. 1698-1706 ◽  
Author(s):  
Julia E. Raftos ◽  
Stephney Whillier ◽  
Bogdan E. Chapman ◽  
Philip W. Kuchel
Keyword(s):  
Human Erythrocytes ◽  
Kinetics Of Uptake ◽  
Kinetics Of

Preparation, optimization and evolution of the kinetic mechanism of an Fe-MIL-88A metal–organic framework

CrystEngComm ◽  
2019 ◽  
Vol 21 (3) ◽  
pp. 544-553 ◽  
Author(s):  
Elham Bagherzadeh ◽  
Seyed Mojtaba Zebarjad ◽  
Hamid Reza Madaah Hosseini ◽  
Pierre Chagnon
Keyword(s):  
Morphological Changes ◽  
Metal Organic Framework ◽  
Kinetic Mechanism ◽  
Nucleation Mechanism ◽  
Growth Behavior ◽  
Kinetics Of Crystallization ◽  
Metal Organic ◽  
Statistical Studies ◽  
Kinetics Of ◽  
Organic Framework

Investigating the kinetics of crystallization, growth behavior and morphological changes through statistical studies of Fe-MIL-88A suggested an autocatalytic nucleation mechanism.

Detailed kinetics of hydrogen abstraction from trans-decalin by OH radicals: the role of hindered internal rotation treatment

2020 ◽  
Vol 22 (44) ◽  
pp. 25740-25746
Author(s):  
Tam V.-T. Mai ◽  
Lam K. Huynh
Keyword(s):  
Master Equation ◽  
Hydrogen Abstraction ◽  
Kinetic Mechanism ◽  
Oh Radicals ◽  
Rate Model ◽  
Wide Range ◽  
Detailed Kinetics ◽  
Kinetics Of ◽  
Detailed Kinetic Mechanism

The detailed kinetic mechanism of the trans-decalin + OH reaction is firstly investigated for a wide range of conditions (T = 200–2000 K & P = 0.76–76000 Torr) using the M06-2X/aug-cc-pVTZ level and stochastic RRKM-based Master equation rate model.

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