scholarly journals Synchronized Infection of Cell Cultures by Magnetically Controlled Virus

2005 ◽  
Vol 79 (1) ◽  
pp. 622-625 ◽  
Author(s):  
Hillel Haim ◽  
Israel Steiner ◽  
Amos Panet
Keyword(s):  
Adsorption Process ◽  
Diffusion Rate ◽  
Cell Attachment ◽  
Diffusion Limited ◽  
Rate Limiting Step ◽  
Immunodeficiency Virus ◽  
Rate Limiting ◽  
And Diffusion ◽  
Entry Mechanism

ABSTRACT To override the diffusion-limited adsorption step of viral infection, we magnetically synchronized cell attachment. Human immunodeficiency virus type 1-based lentivirus preparations were rendered magnetically reactive by association with magnetite nanoparticles, 50 nm in diameter. Application of a magnetic field resulted in immediate redistribution of the viral inoculum to the cell-associated state and completion of the productive adsorption process within 1 min. Independent of adsorption time, viral concentration, and diffusion rate, infection subsequently progressed by the receptor-mediated entry mechanism. Synchronization of this rate-limiting step of infection may now be applied to analyze isolated events in the viral replication sequence.

scholarly journals The Six-Helix Bundle of Human Immunodeficiency Virus Env Controls Pore Formation and Enlargement and Is Initiated at Residues Proximal to the Hairpin Turn

2009 ◽  
Vol 83 (19) ◽  
pp. 10048-10057 ◽  
Author(s):  
Ruben M. Markosyan ◽  
Michael Y. Leung ◽  
Fredric S. Cohen
Keyword(s):  
Human Immunodeficiency Virus ◽  
Coiled Coil ◽  
Fusion Pore ◽  
Helix Bundle ◽  
Rate Limiting Step ◽  
Immunodeficiency Virus ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Pore Enlargement

ABSTRACT Residues that create the grooves of the human immunodeficiency virus type 1 (HIV-1) Env triple-stranded coiled coil (HR1) and the residues that pack into the grooves (HR2) to complete the formation of the six-helix bundle (6HB) were mutated. The extent and kinetics of fusion as well as pore enlargement were measured for each mutant. Mutations near the hairpin turns of each monomer of the 6HB were more important than those far from the turn, for both HR1 and HR2. This result is consistent with the idea that binding of HR2 to the HR1 grooves is initiated near the hairpin turn of each monomer. Mutations at the distal portions also reduced fusion, albeit to a smaller extent. An intermediate of fusion (temperature-arrested state [TAS]) was formed, and the consequences of mutation were compared; a mutant that exhibited less fusion also showed slower kinetics from TAS. This suggests that formation of the bundle is a rate-limiting step downstream of the intermediate state. The rate of enlargement of a fusion pore also correlated with the extent and kinetics of fusion. The rate of pore enlargement was severely reduced by mutation. This supports our prior conclusion that formation of the 6HB occurs after pore creation and strongly suggests that the free energy released by bundle formation is directly used to promote pore growth.

scholarly journals Study on the Adsorption Kinetics of Acid Red 3B on Expanded Graphite

2008 ◽  
Vol 5 (4) ◽  
pp. 802-809 ◽  
Author(s):  
Xiu-yan Pang ◽  
Fei Gong
Keyword(s):  
Activation Energy ◽  
Adsorption Kinetics ◽  
Adsorption Process ◽  
Expanded Graphite ◽  
Chemical Oxidation ◽  
Adsorption Rate ◽  
Order Kinetic ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Expanded graphite (EG) is a kind of important adsorbent for organic compound such as oil and dyes. We have investigated the adsorption kinetics characteristics of this adsorbent for dye. EG was prepared with 50 mesh crude graphite through chemical oxidation intercalation of potassium permanganate and vitriol, and dye of acid red 3B was used as model sorbate. We have studied the adsorption kinetic models and rate-limiting step of the process. Adsorption rate and activation energy of the adsorption process were calculated. Kinetic studies show that the kinetic data are well described by the pseudo second-order kinetic model. The equilibrium adsorbance increases with the increase of the initial acid red 3B concentration. Initial adsorption rate increases with the increase of the initial dye concentration and temperature. Adsorption process of acid red 3B on EG has small activation energy. Internal diffusion appears to be the rate-limiting step for the adsorption process.

Wavelet Based Structural Analysis of Electroless Deposits in the Diffusion Limited Regime

1994 ◽  
Vol 367 ◽  
Author(s):  
A. Arneodo ◽  
F. Argoul ◽  
A. Kuhn ◽  
J.F. Muzy
Keyword(s):  
Electroless Deposition ◽  
Side Reactions ◽  
Statistical Features ◽  
Diffusion Limited ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Fractal Patterns ◽  
Rate Limiting ◽  
Comparative Structural Characterization

AbstractWe discuss the actual relevance of thin gap geometry electrodeposition to generate fractal patterns that mimic the morphology of Witten and Sander's diffusion-limited aggregates (DLA). Eliminating migration and convection, as well as electrochemical side reactions, we show that electroless deposition is a good candidate to meet the requirements for diffusion to be the rate limiting step of the growth process. We use the wavelet transform microscope to achieve a comparative structural characterization of both experimental electroless deposits and numerical DLA clusters. The fact that five-fold symmetry and Fibonacci hierarchical ordering are found as common predominant statistical features is, to our knowledge, the first demonstration, relying on an appropriate structural fractal analysis, of the existence of DLA morphologies in an experimental context.

scholarly journals Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-Linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency

2020 ◽  
Vol 17 (3) ◽  
pp. 788 ◽  
Author(s):  
Daixi Zhou ◽  
Guangyu Xie ◽  
Xinjiang Hu ◽  
Xiaoxi Cai ◽  
Yunlin Zhao ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Adsorption Process ◽  
Reaction System ◽  
Freundlich Isotherm ◽  
Fractional Factorial ◽  
Separation Performance ◽  
Initial Concentration ◽  
Rate Limiting Step ◽  
Rate Limiting ◽  
Competing Ions

Cr(VI) contamination has posed great threat to both the ecosystem and human health for its carcinogenic and mutagenic nature. A highly effective adsorbent for the removal of Cr(VI) was prepared and its adsorption mechanism was thoroughly discussed in this study. In detail, magnetic BiFeO3 and kenaf biochar were loaded on cross-linked chitosan to obtain chitosan-kenaf biochar@BiFeO3 (CKB) for improving adsorption capacity towards Cr(VI). The adsorption process of Cr(VI) onto CKB was evaluated as a function of the pH, the existence of competing ions, the initial concentration of Cr(VI) and contact time. The results show that CKB exhibits the highest adsorption capacity under the optimal pH 2.0. The presence of competing ions such as Ca2+, NO3−, SO42−, and Cl− decreases the adsorption capacity; among them, Ca2+ and NO3− show the greatest hindrance. By studying the effect of initial Cr(VI) concentration on the adsorption capacity, it was found that CKB in the solution was enough to remove Cr(VI) for all treatments (10–200 mg/L). The adsorption experimental data were well fitted with pseudo-first-order model, suggesting that chemisorption is not the dominant rate-limiting step. Freundlich isotherm model can better explain the adsorption process, indicating a non-ideal adsorption towards Cr(VI) on a heterogeneous surface of CKB. A 25-1 Fractional Factorial Design (FFD) showed that pH and initial concentration of Cr(VI) have significant influence on Cr(VI) adsorption in our reaction system. In general, excellent adsorption efficiency of CKB indicates that it may be a good candidate for the remediation of Cr(VI)-contaminating wastewater.

scholarly journals Acetylation turns leucine into a drug by membrane transporter switching

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Grant C. Churchill ◽  
Michael Strupp ◽  
Cailley Factor ◽  
Tatiana Bremova-Ertl ◽  
Mallory Factor ◽  
...  
Keyword(s):  
Amino Acid ◽  
Rational Design ◽  
Organic Anion ◽  
Tissue Expression ◽  
Monocarboxylate Transporter ◽  
Anion Transporters ◽  
Rate Limiting Step ◽  
Acetyl Group ◽  
Rate Limiting

AbstractSmall changes to molecules can have profound effects on their pharmacological activity as exemplified by the addition of the two-carbon acetyl group to make drugs more effective by enhancing their pharmacokinetic or pharmacodynamic properties. N-acetyl-d,l-leucine is approved in France for vertigo and its l-enantiomer is being developed as a drug for rare and common neurological disorders. However, the precise mechanistic details of how acetylation converts leucine into a drug are unknown. Here we show that acetylation of leucine switches its uptake into cells from the l-type amino acid transporter (LAT1) used by leucine to organic anion transporters (OAT1 and OAT3) and the monocarboxylate transporter type 1 (MCT1). Both the kinetics of MCT1 (lower affinity compared to LAT1) and the ubiquitous tissue expression of MCT1 make it well suited for uptake and distribution of N-acetyl-l-leucine. MCT1-mediated uptake of a N-acetyl-l-leucine as a prodrug of leucine bypasses LAT1, the rate-limiting step in activation of leucine-mediated signalling and metabolic process inside cells such as mTOR. Converting an amino acid into an anion through acetylation reveals a way for the rational design of drugs to target anion transporters.

EQUILIBRIUM AND KINETIC STUDIES OF THE ADSORPTION OF 2,4-D AND PICLORAM ON HUMIC ACID

1973 ◽  
Vol 53 (4) ◽  
pp. 429-434 ◽  
Author(s):  
S. U. KHAN
Keyword(s):  
Humic Acid ◽  
Adsorption Process ◽  
Initial Period ◽  
Kinetic Studies ◽  
Time Intervals ◽  
Rate Limiting Step ◽  
Equilibrium Data ◽  
Dichlorophenoxy Acetic Acid ◽  
Rate Limiting ◽  
Physical Type

Equilibrium and kinetic studies of the adsorption of 2,4-D (2,4-dichlorophenoxy acetic acid) and picloram (4-amino-3,5,6-trichloropicolinic acid) on a humic acid have been made. The equilibrium data followed the Freundlich-type isotherm. Rate constants, activation energies, heats of activation, and entropies of activation were calculated for the adsorption of the two herbicides on humic acid. The rate data indicated a physical type of adsorption. In the overall adsorption process the rate-limiting step for the initial period was shown to be the diffusion of the herbicide molecules to the surface of humic acid. However, the rate-limiting process at longer time intervals was interpreted to be intraparticle diffusion of the herbicide molecules into the interior of the humic acid particles.

Kinetics and Isotherm Studies on Nd(III) Adsorption onto Xanthated Chitosan

2016 ◽  
Vol 857 ◽  
pp. 530-534 ◽  
Author(s):  
Noorul Farhana Md Ariff ◽  
Megat Ahmad Kamal Megat Hanafiah ◽  
Zurhana Mat Hussin ◽  
Shariff Che Ibrahim ◽  
Wan Saime Wan Ngah
Keyword(s):  
Metal Ion ◽  
Adsorption Process ◽  
Earth Metal ◽  
Hydroxyl Groups ◽  
Optimum Conditions ◽  
Order Model ◽  
Adsorbent Dosage ◽  
Rate Limiting Step ◽  
Pseudo Second Order ◽  
Rate Limiting

Xanthated chitosan (XC) beads synthesized from the reaction between sulphur and hydroxyl groups were applied to adsorb rare earth metal ion, Nd (III). Adsorption of Nd (III) was found to be a function of pH of initial solution, adsorbent dosage and contact time. The optimum conditions for Nd (III) adsorption were at pH 3 and adsorbent dosage of 0.02 g. Rapid adsorption process was observed as it took only 10 min for reaching the equilibrium state. Chemisorption was identified as the rate limiting step and the kinetics data correlated well with the pseudo-second-order model.

A study of kinetics and successive sorption/desorption of Zn and Cd uptake onto iron-modified zeolite

Clay Minerals ◽  
2015 ◽  
Vol 50 (1) ◽  
pp. 117-132 ◽  
Author(s):  
Marin Ugrina ◽  
Nediljka Vukojević Medvidović ◽  
Jelena Perić ◽  
Marina Trgo
Keyword(s):  
Electrolyte Solutions ◽  
Approximation Model ◽  
Diffusion Kinetic ◽  
Cd Uptake ◽  
Modified Zeolite ◽  
Rate Limiting Step ◽  
Intra Particle Diffusion ◽  
Rate Limiting ◽  
Kinetics Of ◽  
And Diffusion

AbstractThe sorption properties of iron-modified zeolite (IMZ) and the kinetics of zinc and cadmium uptake by the IMZ were investigated by the batch method. Two kinetic stages were observed, fast uptake up to 240 min, followed by slow uptake up to equilibrium. Kinetic results were fitted to the reaction and diffusion kinetic models, which indicated that intra-particle diffusion was the rate-limiting step. The Vermeulen’s approximation model was used to predict the quantity of Zn and Cd ions removed per gram of IMZ. The results of the successive sorption and desorption of Zn and Cd ions, with different electrolyte solutions, showed the best desorption efficiency with sodium salt solutions. Four successive repetitions of the sorption/desorption cycles showed a small difference between the amount of sorbed and desorbed Zn and Cd ions from the second to the fourth cycle. This indicates excellent sorption/regeneration properties of the IMZ.

scholarly journals Identification of an Arg-Gly-Asp (RGD) cell adhesion site in human immunodeficiency virus type 1 transactivation protein, tat.

1990 ◽  
Vol 111 (3) ◽  
pp. 1275-1281 ◽  
Author(s):  
D A Brake ◽  
C Debouck ◽  
G Biesecker
Keyword(s):  
Human Immunodeficiency Virus ◽  
Cell Adhesion ◽  
Cell Lines ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Cell Attachment ◽  
Dependent Manner ◽  
Immunodeficiency Virus ◽  
Hiv 1

Tat, the transactivation factor of human immunodeficiency virus type 1 (HIV-1), contains the highly conserved tripeptide sequence Arg-Gly-Asp (RGD) that characterizes sites for integrin-mediated cell adhesion. The tat protein was assayed for cell attachment activity by measuring the adhesion of monocytic, T lymphocytic, and skeletal muscle-derived cell lines to tat-coated substratum. All cell lines tested bound to tat in a dose-dependent manner and the tat cell adhesion required the RGD sequence because tat mutants constructed to contain an RGE or KGE tripeptide sequence did not mediate efficient cell adhesion. The tat-mediated cell attachment also required divalent cations and an intact cytoskeleton. In addition, cell adhesion to tat was inhibited in the presence of an RGD-containing peptide GRGDSPK or an anti-tat mAb that recognizes the RGD epitope. These results strongly suggest that cells are bound to tat through an integrin. Interestingly, myoblast cells bound to tat remained round, whereas the same cells attached through an integrin for a matrix protein typically flatten and spread. The role of this RGD-dependent cellular adhesion of tat in HIV-1 infection remains to be determined.

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