scholarly journals Conformational variation in superhelical deoxyribonucleic acid

1978 ◽  
Vol 171 (1) ◽  
pp. 281-283 ◽  
Author(s):  
A M Campbell
Keyword(s):  
Light Scattering ◽  
Ionic Strength ◽  
Structural Transition ◽  
Deoxyribonucleic Acid ◽  
Dna Molecules ◽  
Experimental Conditions ◽  
Low Ionic Strength

Sedimentation experiments have shown that superhelical DNA undergoes a sharp structural transition at low ionic strength. Light-scattering experiments show that this is due to a change in conformation of the DNA rather than to a change in interactions among DNA molecules. The results show that two possible conformations can occur for superhelical DNA under routine experimental conditions and may explain the discrepancies in the number of early unwinding sites exposed by different techniques.

scholarly journals The effect of heavy chain phosphorylation and solution conditions on the assembly of Acanthamoeba myosin-II.

1989 ◽  
Vol 109 (4) ◽  
pp. 1529-1535 ◽  
Author(s):  
J H Sinard ◽  
T D Pollard
Keyword(s):  
Light Scattering ◽  
Ionic Strength ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Critical Concentration ◽  
Myosin Ii ◽  
Acidic Ph ◽  
Thick Filaments ◽  
Low Ionic Strength

At low ionic strength, Acanthamoeba myosin-II polymerizes into bipolar minifilaments, consisting of eight molecules, that scatter about three times as much light as monomers. With this light scattering assay, we show that the critical concentration for assembly in 50-mM KCl is less than 5 nM. Phosphorylation of the myosin heavy chain over the range of 0.7 to 3.7 P per molecule has no effect on its KCl dependent assembly properties: the structure of the filaments, the extent of assembly, and the critical concentration for assembly are the same. Sucrose at a concentration above a few percent inhibits polymerization. Millimolar concentrations of MgCl2 induce the lateral aggregation of fully formed minifilaments into thick filaments. Compared with dephosphorylated minifilaments, minifilaments of phosphorylated myosin have a lower tendency to aggregate laterally and require higher concentrations of MgCl2 for maximal light scattering. Acidic pH also induces lateral aggregation, whereas basic pH leads to depolymerization of the myosin-II minifilaments. Under polymerizing conditions, millimolar concentrations of ATP only slightly decrease the light scattering of either phosphorylated or dephosphorylated myosin-II. Barring further modulation of assembly by unknown proteins, both phosphorylated and dephosphorylated myosin-II are expected to be in the form of minifilaments under the ionic conditions existing within Acanthamoeba.

Comparison between specific surface complexation and Donnan ion-exchange models for describing the adsorption of cations on kraft fibres – literature evidence and EXAFS study of Cu(II) binding

2010 ◽  
Vol 25 (2) ◽  
pp. 178-184 ◽  
Author(s):  
Ola Sundman ◽  
Per Persson ◽  
Lars-Olof Öhman
Keyword(s):  
Ionic Strength ◽  
Ion Exchange ◽  
Metal Ion ◽  
Experimental Conditions ◽  
Cellulose Fibres ◽  
Metal Ion Adsorption ◽  
Literature Evidence ◽  
Trivalent Cations ◽  
Exafs Study ◽  
Low Ionic Strength

Abstract A compilation of the applied experimental conditions when studying metal ion adsorption onto kraft fibres, and the resulting conclusion, revealed that the ionic strength conditions used during the experiments were an important dividing factor. At low ionic strengths, the conclusion has regularly been that the Donnan ion-exchange model could correctly predict the adsorption while, at higher ionic strengths, it has often been concluded that the formation of specific metal-ion fibre complexes must be assumed. To study this apparent influence from the presence of monovalent sodium ions, Cu K-edge EXAFS spectra of Cu2+ ions adsorbed to kraft fibres were collected in media of “0” to 100 mM NaCl. Combined with previous data, these measurements confirmed that at very low ionic strength, the importance of specific interactions between the chemically modified cellulose fibres and the Cu(II) ions significantly decreased. For a detailed description of the adsorption phenomenon, both types of interactions must be considered simultaneously. For most technical and engineering applications, however, the Donnan model can be used at low ionic strength conditions, i.e. I ≲ 10 mM. At higher ionic strengths, though, the inclusion of specific complexes in the model is necessary for correctly describing the adsorption of di- and trivalent cations with strong complex forming properties.

scholarly journals The mechanism of assembly of Acanthamoeba myosin-II minifilaments: minifilaments assemble by three successive dimerization steps.

1989 ◽  
Vol 109 (4) ◽  
pp. 1537-1547 ◽  
Author(s):  
J H Sinard ◽  
W F Stafford ◽  
T D Pollard
Keyword(s):  
Electron Microscopy ◽  
Light Scattering ◽  
Ionic Strength ◽  
Analytical Ultracentrifugation ◽  
Myosin Ii ◽  
Alkaline Ph ◽  
Predominant Species ◽  
Assembly Mechanism ◽  
Rapid Equilibrium ◽  
Low Ionic Strength

We used 90 degrees light scattering, analytical ultracentrifugation, and electron microscopy to deduce that Acanthamoeba myosin-II minifilaments, composed of eight molecules each, assemble by a novel mechanism consisting of three successive dimerization steps rather than by the addition of monomers or parallel dimers to a nucleus. Above 200 mM KCl, Acanthamoeba myosin-II is monomeric. At low ionic strength (less than 100 mM KCl), myosin-II polymerizes into bipolar minifilaments. Between 100 and 200 mM KCl, plots of light scattering vs. myosin concentration all extrapolate to the origin but have slopes which decrease with increasing KCl. This indicates that structures intermediate in size between monomers and full length minifilaments are formed, and that the critical concentrations for assembly of these structures is very low. Analytical ultracentrifugation has confirmed that intermediate structures exist at these salt concentrations, and that they are in rapid equilibrium with each other. We believe these structures represent assembly intermediates and have used equilibrium analytical ultracentrifugation and electron microscopy to identify them. Polymerization begins with the formation of antiparallel dimers, with the two tails overlapping by approximately 15 nm. Two antiparallel dimers then associated with a 15-nm stagger to form an antiparallel tetramer. Finally, two tetramers associate with a 30-nm stagger to form the completed minifilament. At very low ionic strengths, the last step in the assembly mechanism is largely reversed and antiparallel tetramers are the predominant species. Alkaline pH, which can also induce minifilament disassembly, produces the same assembly intermediates as are found for salt induced disassembly.

scholarly journals Calibration-Less DNA Concentration Measurements Using EOF Volumetric Flow and Single Molecule Counting

2021 ◽  
Vol 3 ◽  
Author(s):  
Nasim Farajpour ◽  
Lauren S. Lastra ◽  
Vinay Sharma ◽  
Kevin J. Freedman
Keyword(s):  
Ionic Strength ◽  
Electric Field ◽  
Single Molecule ◽  
Capture Rate ◽  
Volumetric Flow Rate ◽  
Dna Molecules ◽  
Element Analysis ◽  
Dna Concentration ◽  
Dna Capture ◽  
Low Ionic Strength

Nanopore sensing is a promising tool well suited to capture and detect DNA and other single molecules. DNA is a negatively charged biomolecule that can be captured and translocated through a constricted nanopore aperture under an applied electric field. Precise assessment of DNA concentration is of crucial importance in many analytical processes and medical diagnostic applications. Recently, we found that hydrodynamic forces can lead to DNA motion against the electrophoretic force (EPF) at low ionic strength. This study utilized glass nanopores to investigate the DNA capture mechanism and detect DNA molecules due to volumetric flow at these low ionic strength conditions. We measured the DNA capture rate at five different pico-molar concentrations. Our findings indicated that the translocation rate is proportional to the concentration of DNA molecules and requires no calibration due to the volumetric flow rate and DNA counting directly correlates with concentration. Using finite element analysis, we calculated the volumetric flow and proposed a simple, straightforward approach for accurate DNA quantification. Furthermore, these experiments explore a unique transport mechanism where one of the most highly charged molecules enters a pore against electric field forces. This quantitative technique has the potential to provide distinct insight into nanopore-based biosensing and further enhance the nanopore’s capability as a biomolecule concentration sensor.

Correlation between Ca2+-ATPase activity of rat islet cells and insulin secretion

1992 ◽  
Vol 134 (2) ◽  
pp. 221-225 ◽  
Author(s):  
C. M. Gronda ◽  
G. B. Diaz ◽  
J. P. F. C. Rossi ◽  
J. J. Gagliardino
Keyword(s):  
Enzyme Activity ◽  
Insulin Secretion ◽  
Ionic Strength ◽  
Atpase Activity ◽  
Islet Cells ◽  
Experimental Conditions ◽  
Physiological Regulation ◽  
Enhancing Effect ◽  
Cellular Targets ◽  
Low Ionic Strength

ABSTRACT Using medium with a low ionic strength, a low concentration of Ca2+ and Mg2+ and devoid of K+, we have measured Ca2+-ATPase activity in the homogenates of rat islets preincubated for 3 min with several hormones in the presence of 3·3 mmol glucose/l. Insulin secretion was also measured in islets incubated for 5 min under identical experimental conditions. Islets preincubated with glucose (3·3 mmol/l) and glucagon (1·4 μmol/l) plus theophylline (10 mmol/l), ACTH (0·11 nmol/l), bovine GH (0·46 μmol/l), prolactin (0·2 μmol/l) or tri-iodothyronine (1·0 nmol/l) have significantly lower Ca2+-ATPase activity than those preincubated with only 3·3 mmol glucose/l. All these hormones increased the release of insulin significantly. Dexamethasone (0·1 μmol/l) and somatostatin (1·2 μmol/l) enhanced the Ca2+-ATPase activity while adrenaline (10 μmol/l) did not produce any significant effect on the activity of the enzyme. These hormones decreased the release of insulin significantly. These results demonstrated that islet Ca2+-ATPase activity was modulated by the hormones tested. Their inhibitory or enhancing effect seemed to be related to their effect on insulin secretion; i.e. those which stimulated the secretion of insulin inhibited the activity of the enzyme and vice versa. Hence, their effect on insulin secretion may be due, in part, to their effect on enzyme activity and consequently on the concentration of cytosolic Ca2+. These results reinforce the assumption that Ca2+-ATPase activity participates in the physiological regulation of insulin secretion, being one of the cellular targets for several agents which affect this process. Journal of Endocrinology (1992) 134, 221–225

scholarly journals Conformational analysis of deoxyribonucleic acid from PM2 bacteriophage. The effect of size on supercoil shape

1976 ◽  
Vol 155 (1) ◽  
pp. 101-105 ◽  
Author(s):  
A M Campbell
Keyword(s):  
Light Scattering ◽  
Ionic Strength ◽  
Deoxyribonucleic Acid ◽  
Laser Light ◽  
Structural Models ◽  
Laser Light Scattering ◽  
Mean Square ◽  
Planar Molecule ◽  
The One ◽  
Experimental Interference

Laser light-scattering studies of bacteriophage PM2 DNA showed the molecule to have mol.wt. 5.9 } 10(6) and root-mean -square radius 125 nm at an ionic strength of 0.2 mol/litre. Computer-generated curves compatible with these data were compared with the experimental interference curve for several structural models of the molecules. The data fit best to an asymmetric four-armed planar molecule in which all four arms emerge from or close to the one area of the molecule. This contrasts with the smaller DNA molecules investigated, which have shown a three-armed molecule, whose symmetry varies with primary structure.

Rheological and Light Scattering Studies of Cationic Fluorocarbon Surfactant Solutions at Low Ionic Strength

Langmuir ◽  
2002 ◽  
Vol 18 (8) ◽  
pp. 3076-3085 ◽  
Author(s):  
Cl. Oelschlaeger ◽  
G. Waton ◽  
E. Buhler ◽  
S. J. Candau ◽  
M. E. Cates
Keyword(s):  
Light Scattering ◽  
Ionic Strength ◽  
Fluorocarbon Surfactant ◽  
Surfactant Solutions ◽  
Low Ionic Strength
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