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

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.

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 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 Deep-etch visualization of 27S clathrin: a tetrahedral tetramer.

1987 ◽  
Vol 105 (5) ◽  
pp. 1999-2009 ◽  
Author(s):  
J E Heuser ◽  
J H Keen ◽  
L M Amende ◽  
R E Lippoldt ◽  
K Prasad
Keyword(s):  
Electron Microscopy ◽  
Light Scattering ◽  
Ionic Strength ◽  
Sulfonic Acid ◽  
Freeze Drying ◽  
Sulfate Solutions ◽  
Quick Freezing ◽  
Freeze Etching ◽  
Low Ionic Strength ◽  
Equilibrium Centrifugation

It has recently been reported that 8S clathrin trimers or "triskelions" form larger 27S oligomers upon dialysis into low ionic strength buffers (Prasad, K., R. E. Lippoldt, H. Edelhoch, and M. S. Lewis, 1986, Biochemistry, 25:5214-5219). Here, deep-etch electron microscopy of the 27S species reveals that they are closed tetrahedra composed of four clathrin triskelions. This was determined by two approaches. First, standard quick-freezing and freeze-etching of unfixed 27S species suspended in 2 mM 2-(N-morpholino)ethane sulfonic acid (MES) buffer, pH 5.9, yielded unambiguous images of tetrahedra that measured 33 nm on each edge. Second, the technique of freeze-drying molecules on mica (Heuser, J. E., 1983, J. Mol. Biol., 169:155-195) was modified to overcome the low affinity of mica in 2 mM MES, by pretreating the mica with polylysine. Thereafter, 27S species adsorbed avidly to it and collapsed into characteristic configurations containing four globular domains, each linked to the others by three approximately 33-nm struts. The globular domains look like vertices of deep-etched clathrin triskelions and the links, numbering 12 in all, look like four sets of triskelion legs. New light scattering and equilibrium centrifugation data confirm that 27S polymer is four times as massive as one clathrin triskelion. We conclude that in conditions that do not favor the formation of standard clathrin cages, low affinity interactions lead to closed, symmetrical assemblies of four triskelions, each of which assumes a unique puckered, straight-legged configuration to create the edges of a tetrahedron. Tetrahedra are similar in construction to the cubic octomers of clathrin recently found in ammonium sulfate solutions (Sorger, P. K., R. A. Crowther, J. T. Finch, and B. M. F. Pearse, 1986, J. Cell Biol., 103:1213-1219) but are still smaller, involving only half as many clathrin triskelions.

Quasielastische Lichtstreuung von isoliertem Chromatin / Quasielastic Light Scattering of Isolated Chromatin

1983 ◽  
Vol 38 (1-2) ◽  
pp. 126-134 ◽  
Author(s):  
Bernd Meuel ◽  
Holger Notbohm
Keyword(s):  
Light Scattering ◽  
Ionic Strength ◽  
Structural Changes ◽  
Gel Chromatography ◽  
Quasielastic Light Scattering ◽  
Self Assembling ◽  
X Ray Scattering ◽  
Monovalent Salt ◽  
Quaternary Structures ◽  
Low Ionic Strength

Chromatin undergoes structural changes in dependence on the ionic strength of monovalent cations. At low ionic strength an extended chain of nucleosomes is apparent while with increasing ionic strength more compact structures are formed. Soluble chromatin was prepared from rat liver and fractionated by gel chromatography. Quasielastic light scattering experiments on chromatin were done with monovalent salt concentrations ranging from 3-150 mм. Using this method translational diffusion coefficients have been derived. These appeared to be nearly independent of monovalent salt concentrations, indicating that the hydrodynamic radius of chromatin molecules did not change. On the other hand, sedimentation coefficients were increasing according to an exponential relation. Taken together, both findings reveal a rising of the molar mass with increasing ionic strength. On the contrary, chromatin prepared in physiological salt apparently disintegrates by lowering the ionic strength. Furthermore, it could be demonstrated by earlier small angle X-ray scattering studies that the diameter of the higher order chromatin fiber remained constant at approximately 32 nm even if these structures had been reconstituted from smaller pieces starting at low ionic strength. Thus, isolated chromatin fibers are capable of self-assembling to regular quaternary structures, even if the DNA does not form a continuous strand.

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