scholarly journals Cytological Effects of Prefixation Treatment

1958 ◽  
Vol 4 (4) ◽  
pp. 391-400 ◽  
Author(s):  
David A. Hungerford ◽  
Marie DiBerardino
Keyword(s):  
Ionic Strength ◽  
Osmotic Pressure ◽  
Divalent Cations ◽  
Macromolecular Structure ◽  
Sucrose Solutions ◽  
Subsequent Exposure ◽  
Mouse Fetuses ◽  
Low Ionic Strength ◽  
Neurula Stage

The effects produced by prefixation treatments on cells in metaphase from 10-day mouse fetuses and from several embryonic stages of the frog were investigated. The technical value of some of these pretreatments is noted. Pretreatment with isotonic solutions (both ionic and non-ionic in the case of the mouse, ionic only in the frog) generally produced a similar effect, viz., chromosomal swelling with little effect on the spindle. A notable exception is provided by frog embryos preceding the neurula stage; spindle disorganization without chromosomal swelling was produced by pretreatment in isotonic modified Niu-Twitty solution, containing no divalent cations. Pretreatment with hypotonic solutions (both ionic and non-ionic in the case of the mouse, ionic only in the frog) generally produced several major effects, viz., despiralization of chromosomes, chromatid separation, and spindle disorganization. The conclusion is drawn from the mouse data that, in order to produce these effects, pretreating solutions must be of low osmotic pressure. Low ionic strength alone (e.g., isotonic sucrose solutions) is not sufficient. As differentiation of frog embryos progressed, pretreatments either of longer duration or with solutions of increasing degrees of hypotonicity were required to produce comparable intensities of the same effects. Many of the effects on metaphases produced by hypotonic pretreatment of frog embryos were reversible by subsequent exposure to isotonic solutions. The significance of results presented here is discussed briefly with respect to some current considerations of the macromolecular structure of chromosomes.

Filament Formation by Slime Mould Myosin Isolated at Low Ionic Strength

1974 ◽  
Vol 15 (1) ◽  
pp. 113-129
Author(s):  
H. HINSSEN ◽  
J. D'HAESE
Keyword(s):  
Ionic Strength ◽  
Striated Muscle ◽  
Divalent Cations ◽  
Filament Formation ◽  
Selective Precipitation ◽  
Slime Mould ◽  
Preparation Conditions ◽  
Filament Structure ◽  
Low Ionic Strength

Myosin was isolated and purified from plasmodia of the slime mould Physarum polycephalum by a new method. This method is based on actomyosin extraction at low ionic strength after extensive washing, followed by the selective precipitation of myosin at pH 6.1 under relaxing conditions. The yield of myosin was 3-5 times higher than reported for other methods. In contrast to earlier studies a remarkably strong tendency to filament formation was found for slime mould myosin, probably due to a better preservation of some structural properties during preparation. Conditions were worked out under which numerous filaments up to 4 µm in length can be produced. It was established that not only a gradual decrease of ionic strength may influence filament formation, but also pH, ATP concentration and the presence of divalent cations. Compared to the current filament models a difference exists in the structure of the filaments. No central bare zone can be found, and thus, they lack an apparent bipolarity. Along the entire filament there are lateral projections representing the head portion of myosin molecules. A clear periodicity with an axial repeat of about 14 nm was observed, indicating a highly ordered arrangement of these projections. In this paper it is shown for the first time that myosin from one of the primitive motile systems is able to form aggregates of high structural order, indicating that the contraction of non-muscular actomyosin systems is not necessarily effected with oligomeric or randomly aggregated myosin. The possible role of myosin aggregation in vivo and the similarity of filament structure to that recently reported for myosin from vertebrate smooth muscle and striated muscle are discussed.

scholarly journals Coat proteins isolated from clathrin coated vesicles can assemble into coated pits.

1989 ◽  
Vol 108 (5) ◽  
pp. 1615-1624 ◽  
Author(s):  
D T Mahaffey ◽  
M S Moore ◽  
F M Brodsky ◽  
R G Anderson
Keyword(s):  
Ionic Strength ◽  
Plasma Membranes ◽  
Divalent Cations ◽  
Low Ph ◽  
Coated Vesicles ◽  
Coat Proteins ◽  
Coated Pits ◽  
Ph Buffer ◽  
Solid Substratum ◽  
Low Ionic Strength

Isolated human fibroblast plasma membranes that were attached by their extracellular surface to a solid substratum contained numerous clathrin coated pits that could be removed with a high pH buffer (Moore, M.S., D.T. Mahaffey, F.M. Brodsky, and R.G.W. Anderson. 1987. Science [Wash. DC]. 236:558-563). When these membranes were incubated with coat proteins extracted from purified bovine coated vesicles, new coated pits formed that were indistinguishable from native coated pits. Assembly was dependent on the concentration of coat protein with half maximal assembly occurring at 7 micrograms/ml. Assembly was only slightly affected by the presence of divalent cations. Whereas normal appearing lattices formed in a low ionic strength buffer, when assembly was carried out in a low pH buffer, few coated pits were evident but numerous small clathrin cages decorated the membrane. Coated pits did not form randomly on the surface; instead, they assembled at differentiated regions of membrane that could be distinguished in carbon/platinum replicas of frozen and etched membranes by the presence of numerous particles clustered into patches the size and shape of a coated pit.

scholarly journals Size distribution of FEBEX bentonite colloids upon fast disaggregation in low-ionic strength water

Clay Minerals ◽  
2016 ◽  
Vol 51 (2) ◽  
pp. 213-222 ◽  
Author(s):  
Natalia Mayordomo ◽  
Claude Degueldre ◽  
Ursula Alonso ◽  
Tiziana Missana
Keyword(s):  
Ionic Strength ◽  
Size Distribution ◽  
Divalent Cations ◽  
Time Frame ◽  
Mixed Electrolytes ◽  
Time Resolved ◽  
Aggregation And Disaggregation ◽  
Bentonite Colloid ◽  
Low Ionic Strength ◽  
Waste Repositories

AbstractBentonite colloids generated from the backfill barrier in nuclear waste repositories may act as radionuclide carriers, if they are stable and mobile. Repository scenarios with highly saline groundwater inhibit colloid stability as particles tend to aggregate but, in the time frame of repositories, groundwater conditions may evolve, promoting particle disaggregation and stabilization. The disaggregation of FEBEX bentonite colloids by fast dilution to lower ionic strength was analysed in this study. Time-resolved dynamic light-scattering experiments were carried out to evaluate the kinetics of bentonite colloid aggregation and disaggregation processes in Na+ and Na+-Ca2+ mixed electrolytes of low ionic strength. Attachment and detachment efficiencies were determined.Aggregation is promoted by increasing ionic strength, being more efficient in the presence of divalent cations. Once bentonite colloids are aggregated, a decrease in ionic strength facilitates disaggregation, but the process is not fully reversible as the initial size of the stable bentonite colloids at low ionic strength is not fully recovered. Particle-size distribution and concentration in suspension were analysed on disaggregated samples by single particle-counting measurements. Small colloids were measured in the disaggregated samples but their population was smaller than in the initial stable sample, especially in the presence of Ca2+.

Electrical stability of erythrocytes in the presence of divalent cations

1988 ◽  
Vol 8 (5) ◽  
pp. 421-426 ◽  
Author(s):  
T. Ch. Tomov ◽  
I. Ch. Tsoneva ◽  
J. Ch. Doncheva
Keyword(s):  
Ionic Strength ◽  
Divalent Cations ◽  
Protective Action ◽  
Electrical Pulse ◽  
Electrostatic Repulsion ◽  
Electrical Stability ◽  
Divalent Ions ◽  
Protein Molecules ◽  
Low Ionic Strength

Erythrocytes suspended in a medium of low ionic strength lyse under the effect of an exponential electrical pulse. The percentage of haemolysed cells decreases several-fold in the presence of divalent cations. The protective action of the ions studied increases in the following order: Ca++, Mg++, Zn++. It is assumed that divalent ions bind to the negative charges of the lipid and protein molecules and reduce their electrostatic repulsion, which results in stabilization of the membranes.

scholarly journals Role of divalent cations on DNA polymorphism under low ionic strength conditions

1986 ◽  
Vol 14 (12) ◽  
pp. 5099-5109 ◽  
Author(s):  
Sundaram Devarajan ◽  
Richard H. Shafer
Keyword(s):  
Ionic Strength ◽  
Dna Polymorphism ◽  
Divalent Cations ◽  
Low Ionic Strength

The self-assembly of synthetic filaments of myosin isolated from Chaos carolinensis and Amoeba proteus

1977 ◽  
Vol 25 (1) ◽  
pp. 387-402
Author(s):  
J.S. Condeelis
Keyword(s):  
Ionic Strength ◽  
Self Assembly ◽  
Divalent Cations ◽  
Central Zone ◽  
Thick Filament ◽  
Amoeba Proteus ◽  
High Ionic Strength ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Low Ionic Strength

Synthetic myosin thick filaments were formed from preparations of electrophoretically homogeneous myosin isolated from Chaos carolinensis and Amoeba proteus when dialysed to physiological ionic strength and pH. Myosin dialysed directly against low ionic strength buffers formed native-like thick filaments in the presence and absence of exogenous divalent cations. The average dimensions of the synthetic filaments grown under these conditions were 455 nm long and 16 nm wide with a distinct bare central zone 174 nm long. Myosin predialysed against EGTA-EDTA solutions at high ionic strength and then dialysed to low ionic strength formed native-like filaments only in the presence of 1mM Mg2+. 1 mM Ca2+ could not be substituted for Mg2+ under these conditions to achieve native-like filaments. Filaments grown from predialysed myosin in the absence of Mg2+ resembled EGTA-dissociated myosin filaments observed in EGTA-treated cytoplasm and were highly branched, poorly formed filaments lacking a distinct bare central zone. The average dimensions of the filaments grown from predialysed myosin in the absence of Mg2+ were 328 nm long, 13 nm wide with a bare central zone 111 nm long. Under the conditions tested, myosin isolated from these amoebae did not demonstrate a divalent cation requirement for thick filament formation. The results obtained with myosin isolated from the 2 organisms were identical.

scholarly journals ATP, uncomplexed by divalent cations, and the LC2 light chain are interdependent modifiers of the skeletal actomyosin MgATPase activity

1991 ◽  
Vol 280 (1) ◽  
pp. 39-44
Author(s):  
S M Pemrick ◽  
P A Martinez
Keyword(s):  
Ionic Strength ◽  
Light Chain ◽  
Divalent Cations ◽  
High Ionic Strength ◽  
Negative Effects ◽  
Thin Filament Regulation ◽  
Skeletal Muscle Contraction ◽  
Wide Range ◽  
Low Ionic Strength ◽  
Mgatpase Activity

In the absence of troponin and tropomyosin, skeletal actomyosin MgATPase activity can be altered by 2-3-fold by divalent cations. The ‘sign’ of this effect (i.e. inhibition or activation) varies with ionic strength. To investigate the mechanism, P(i) liberation was analysed at both low and high ionic strength with three concentrations of MgATP and over a wide range of Mg2+ concentrations. This procedure separated the effects of two dependent variables, Mg2+ and ATP4-/3- (ATPfree), to provide the following observations. (1) ATPfree, not Mg2+ (nor Ca2+), was the modifier. (2) ATPfree was an activator at low ionic strength and an inhibitor at high ionic strength, with half-maximal activation/inhibition occurring between 0.75 and 0.8 mM-ATPfree. (3) The rate constants controlling Vmax. with respect to actin were increased up to 3-fold by ATPfree at low ionic strength, and decreased up to 3-fold by ATPfree at high ionic strength. (4) The effect of ATPfree required near-native levels of the LC2 light chain bound to myosin (i.e. 2 mol of LC2/mol of myosin). (5) Sensitivity of P(i) liberation to a 50% decrease in the LC2 content of myosin required high ATPfree concentrations. It is concluded that LC2 and ATPfree are interdependent, non-additive, modifiers of MgATPase. These results are consistent with thin filament regulation of skeletal muscle contraction, and begin to explain why both positive and negative effects on MgATPase have been attributed to LC2.

Conformational Transitions in Escherichia coli Ribosomal RNAs as Visualized by Dedicated STEM

1988 ◽  
Vol 46 ◽  
pp. 176-177
Author(s):  
J.S. Wall ◽  
V. Maridiyan ◽  
S. Tumminia ◽  
J. Hairifeld ◽  
M. Boublik
Keyword(s):  
Ionic Strength ◽  
Three Dimensional ◽  
Conformational Transitions ◽  
Dark Field ◽  
Dimensional Structure ◽  
Ribosomal Rnas ◽  
Field Mode ◽  
Freeze Dried ◽  
High Resolution Images ◽  
Low Ionic Strength

The high contrast in the dark-field mode of dedicated STEM, specimen deposition by the wet film technique and low radiation dose (1 e/Å2) at -160°C make it possible to obtain high resolution images of unstained freeze-dried macromolecules with minimal structural distortion. Since the image intensity is directly related to the local projected mass of the specimen it became feasible to determine the molecular mass and mass distribution within individual macromolecules and from these data to calculate the linear density (M/L) and the radii of gyration.2 This parameter (RQ), reflecting the three-dimensional structure of the macromolecular particles in solution, has been applied to monitor the conformational transitions in E. coli 16S and 23S ribosomal RNAs in solutions of various ionic strength.In spite of the differences in mass (550 kD and 1050 kD, respectively), both 16S and 23S RNA appear equally sensitive to changes in buffer conditions. In deionized water or conditions of extremely low ionic strength both appear as filamentous structures (Fig. la and 2a, respectively) possessing a major backbone with protruding branches which are more frequent and more complex in 23S RNA (Fig. 2a).

An Evaluation of a Plasma Fractionation System

1960 ◽  
Vol 4 (01) ◽  
pp. 031-044
Author(s):  
George Y. Shinowara ◽  
E. Mary Ruth
Keyword(s):  
Biological Activity ◽  
Ionic Strength ◽  
Plasma Proteins ◽  
High Concentration ◽  
Significant Evidence ◽  
Native Proteins ◽  
Mobility Data ◽  
Fractionation Procedure ◽  
The Individual ◽  
Low Ionic Strength

SummaryFour primary fractions comprising at least 97 per cent of the plasma proteins have been critically appraised for evidence of denaturation arising from a low temperature—low ionic strength fractionation system. The results in addition to those referable to the recovery of mass and biological activity include the following: The high solubilities of these fractions at pH 7.3 and low ionic strengths; the compatibility of the electrophoretic and ultracentrifugal data of the individual fractions with those of the original plasma; and the recovery of hemoglobin, not hematin, in fraction III obtained from specimens contaminated with this pigment. However, the most significant evidence for minimum alterations of native proteins was that the S20, w and the electrophoretic mobility data on the physically recombined fractions were identical to those found on whole plasma.The fractionation procedure examined here quantitatively isolates fibrinogen, prothrombin and antithrombin in primary fractions. Results have been obtained demonstrating its significance in other biological systems. These include the following: The finding of 5 S20, w classes in the 4 primary fractions; the occurrence of more than 90 per cent of the plasma gamma globulins in fraction III; the 98 per cent pure albumin in fraction IV; and, finally, the high concentration of beta lipoproteins in fraction II.

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