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.

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.

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 Multiple supramolecular structures formed by interaction of actin with protamine

1982 ◽  
Vol 205 (1) ◽  
pp. 31-37 ◽  
Author(s):  
Enrico Grazi ◽  
Ermes Magri ◽  
Ivonne Pasquali-Ronchetti
Keyword(s):  
Ionic Strength ◽  
Exchange Reaction ◽  
Dead Time ◽  
High Ionic Strength ◽  
Supramolecular Structures ◽  
Molar Ratio ◽  
First Case ◽  
Atpase Reaction ◽  
Low Ionic Strength ◽  
Millipore Filters

When protamine is added to actin, different supramolecular structures are formed depending on the molar ratio of the two proteins and of the ionic strength of the medium. At low ionic strength, and going from a molar ratio of protamine to G-actin of 4:1, 2:1 and 1:1, globular aggregates are first converted into extended structures and then to long threads in which the constituent ATP–G-actin is rapidly exchangeable with the actin of the medium. At high ionic strength {Tyrode [(1910) Arch. Int. Pharmacodyn. Ther.20, 205–212] solution}, starting from G-actin and protamine in the 1:1 molar ratio, long ropes are formed that can be resolved into intertwining filaments of 4–5nm diameter. The addition of protamine in a 1:1 molar ratio to a solution of F-actin in Tyrode solution causes the breakage of the actin filaments, which is also revealed by the decrease of the viscosity of the solution and the formation of ordered latero-lateral aggregates. The structures formed by reaction of protamine with G-actin can be separated from free G-actin and protamine by filtration through 0.45μm-pore-size Millipore filters. This technique has been exploited to study the exchange reaction between free actin and the actin–protamine complexes. For these studies the 1:1 actin–protamine complex formed at low ionic strength and the 2:1 actin–protamine complex formed in the presence of 23nm-free Mg2+ have been selected. In the first case the exchange reaction is practically complete in the dead time of the experiment (20s). In the second case, where the complex operates like a true ATPase, the rate of the exchange is initially comparable with the rate of the ATP cleavage. Later on, however, the complex undergoes a change and the rate of the exchange between free actin and the actin bound to protamine becomes lower than the rate of the ATPase reaction. It is proposed that the ATP exchanges for ADP directly on the G-actin bound in the complex.

scholarly journals The Use of 2-Chloroethanol for Reversible Depolymerisation of the Protein Shell of Bacteriophage fr

1970 ◽  
Vol 25 (7) ◽  
pp. 711-713 ◽  
Author(s):  
D. Schubert ◽  
H. Frank
Keyword(s):  
Acetic Acid ◽  
Ionic Strength ◽  
Organic Solvent ◽  
High Ionic Strength ◽  
Protein Subunits ◽  
Viruslike Particles ◽  
Low Ionic Strength ◽  
Protein Shell

In mixtures of 1 volume of buffer and 2 volumes of 2-chloroethanol, the icosahedral bacteriophage fr is split into RNA and monomeric protein subunits. After removal of the RNA and after replacement of the organic solvent by water, viruslike particles can be obtained by dialysis of the protein against neutral buffers of high ionic strength, whereas multishell particles are formed in buffers of low ionic strength. All results achieved by the use of 2-chloroethanol are very similar to those obtained using acetic acid.

scholarly journals Some electron-transfer reactions involving carbodi-imide-modified cytochrome c

1987 ◽  
Vol 243 (2) ◽  
pp. 379-384 ◽  
Author(s):  
A J Mathews ◽  
T Brittain
Keyword(s):  
Electron Transfer ◽  
Ionic Strength ◽  
Protein Charge ◽  
Native Proteins ◽  
Wide Range ◽  
Internal Electron ◽  
Modified Proteins ◽  
Time Courses ◽  
Low Ionic Strength ◽  
Kinetics Of

The reaction kinetics of native and carbodi-imide-modified tuna and horse heart cytochromes c with both a strong (dithionite) and a relatively weak (ascorbate) reducing agent were studied over a wide range of conditions. In their reactions with dithionite both the native and modified cytochromes exhibit single exponential time courses. The effects of dithionite concentration and ionic strength on the rate of the reduction are complex and can best be explained in terms of the model proposed by Lambeth & Palmer [(1973) J. Biol. Chem. 248, 6095-6103]. According to this model, at low ionic strength the native proteins are reduced almost exclusively by S2O4(2-) whereas the modified proteins showed reactivity towards both S2O4(2-) and SO2.-. These findings are interpreted in terms of the different charge characteristics of the carbodi-imide-modified proteins relative to the native proteins. The findings that the modified proteins react with ascorbate in a biphasic manner are explained as arising from ascorbate binding to a reducible form of the protein, before electron transfer, with an equilibrium between the ascorbate-reducible form of the protein and a non-reducible form. Estimates were obtained for both the ascorbate equilibrium binding constant and the rate constant for the internal electron transfer for both the native and modified horse and tuna proteins. The effect of pH on the reactions indicates that the active reductant in all cases is ascorbate2-. The studies of ascorbate reactivity yield important information concerning the proposed correlation between ascorbate reducibility and the presence of a 695 nm-absorption band, and the study of dithionite reactivity illustrates the effect of protein charge and solution ionic strength on the relative contributions made by the species SO2.- and S2O4(2-) to the reduction of ferricytochrome c.

scholarly journals Role of the reticulum in the stability and shape of the isolated human erythrocyte membrane

1982 ◽  
Vol 92 (3) ◽  
pp. 714-721 ◽  
Author(s):  
Y Lange ◽  
RA Hadesman ◽  
TL Steck
Keyword(s):  
Ionic Strength ◽  
Erythrocyte Membrane ◽  
Human Erythrocyte ◽  
Time Course ◽  
Isotonic Saline ◽  
Human Erythrocyte Membrane ◽  
Wide Range ◽  
Cell Stability ◽  
Mechanically Stabilized ◽  
Low Ionic Strength

In order to examine the widely held hypothesis that the reticulum of proteins which covers the cytoplamsic surface of the human erythrocyte membrane controls cell stability and shape, we have assessed some of its properties. The reticulum, freed of the bilayer by extraction with Triton X-100, was found to be mechanically stable at physiological ionic strength but physically unstable at low ionic strength. The reticulum broke down after a characteristic lag period which decreased 500-fold between 0 degrees and 37 degrees C. The release of polypeptide band 4.1 from the reticulum preceded that of spectrin and actin, suggesting that band 4.1 might stabilize the ensemble but is not essential to its integrity. The time-course of breakdown was similar for ghosts, the reticulum inside of ghosts, and the isolated reticulum. However, at very low ionic strength, the reticulum was less stable within the ghost than when free; at higher ionic strength, the reverse was true. Over a wide range of conditions the membrane broke down to vesicles just as the reticulum disintegrated, presumably because the bilayer was mechanically stabilized by this network. The volume of both ghosts and naked reticula varied inversely and reversibly with ionic strength. The volume of the naked reticulum varied far more widely than the ghost, suggesting that its deformation was normally limited by the less extensible bilayer. The contour of the isolated reticulum was discoid and often dimpled or indented, as visualized in the fluorescence microscope after labeling of the ghosts with fluoroscein isothiocyanate. Reticula derived from ghosts which had lost the ability to crenate in isotonic saline were shriveled, even though the bilayer was smooth and expanded. Conversly, ghosts crenated by dinitrophenol yielded smooth, expanded reticula. We conclude that the reticulum is a durable, flexible, and elastic network which assumes and stabilizes the contour of the membrane but is not responsible for its crenation.

scholarly journals The composition of cartilage proteoglycans. An investigation using high-and low-ionic-strength extraction procedures

1973 ◽  
Vol 131 (3) ◽  
pp. 541-553 ◽  
Author(s):  
Robert W. Mayes ◽  
Roger M. Mason ◽  
David C. Griffin
Keyword(s):  
Amino Acid ◽  
Ionic Strength ◽  
Density Gradient ◽  
Amino Acid Analysis ◽  
Chondroitin Sulphate ◽  
High Ionic Strength ◽  
Guanidinium Chloride ◽  
Equilibrium Conditions ◽  
Chondroitin Sulphate Proteoglycans ◽  
Low Ionic Strength

1. A proteoglycan fraction (the proteoglycan subunit fraction) was prepared from extracts, with 0.15m-KCl (low-ionic-strength) and 0.5m-LaCl3, 2.0m-CaCl2 and 4.0m-guanidinium chloride (high-ionic-strength), of bovine nasal cartilage by equilibrium-density-gradient centrifugation, essentially as described by Hascall & Sajdera (1969). 2. The use of different centrifugation times showed that near-equilibrium conditions were reached by 48h for the fractions prepared from the high-ionic-strength extracts. The fraction isolated from the low-ionic-strength extract required a longer centrifugation time to reach equilibrium conditions. 3. The composition of the proteoglycan fractions from the various extracts was compared by analyses of their carbohydrate and amino acid contents. Difference indices were calculated from the amino acid analysis to compare the degree of compositional relationship between the protein components of the proteoglycans. 4. Small compositional differences were found between the proteoglycans isolated from the various high-ionic-strength extracts. The protein content of the fractions from the CaCl2 extract and the guanidinium chloride extract showed the greatest difference in this respect, although their amino acid analysis was similar. 5. The proteoglycan fraction isolated from the low-ionic-strength extract shows marked differences in composition from the fractions isolated from the high-ionic-strength extracts. Its protein and glucosamine contents were lower whereas its hexuronic acid and galactosamine contents were higher than those of the latter. It also exhibits major differences in its amino acid composition. The glucosamine:galactosamine ratio of the fraction from the low-ionic-strength extract indicates that it may be an almost exclusively chondroitin sulphate–proteoglycan. Its analysis correlates closely with that of a low-molecular-weight proteoglycan isolated from pig laryngeal cartilage by Tsiganos & Muir (1969). 6. The proteoglycan fractions from both the low- and high-ionic-strength extracts migrate as a single band in zone electrophoresis carried out in a sucrose-density gradient at both pH3.0 and pH7.0, although each showed evidence of band widening during the electrophoresis. All the proteoglycan fractions migrated with the same electrophoretic mobility at pH3.0, irrespective of the differences in composition between them. 7. The differences between the proteoglycans from the low- and high-ionic-strength extracts are discussed and the view is advanced that they may be due to association between predominantly chondroitin sulphate–proteoglycans and a keratan sulphate-enriched proteoglycan species.

scholarly journals Microtubule assembly kinetics. Changes with solution conditions

1987 ◽  
Vol 247 (3) ◽  
pp. 505-511 ◽  
Author(s):  
J S Barton ◽  
D L Vandivort ◽  
D H Heacock ◽  
J A Coffman ◽  
K A Trygg
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Low Temperature ◽  
Number Concentration ◽  
High Ionic Strength ◽  
Microtubule Assembly ◽  
Microtubule Protein ◽  
Assembly Kinetics ◽  
Low Ionic Strength ◽  
Kinetics Of

The assembly kinetics of microtubule protein are altered by ionic strength, temperature and Mg2+, but not by pH. High ionic strength (I0.2), low temperature (T less than 30 degrees C) and elevated Mg2+ (greater than or equal to 1.2 mM) induce a transition from biphasic to monophasic kinetics. Comparison of the activation energy obtained for the fast biphasic step at low ionic strength (I0.069) shows excellent agreement with the values obtained at high ionic strength, low temperature and elevated Mg2+. From this observation it can be implied that the tubulin-containing reactant of the fast biphasic event is also the species that elongates microtubules during monophasic assembly. Second-order rate constants for biphasic assembly are 3.82(+/- 0.72) x 10(7) M-1.s-1 and 5.19(+/- 1.25) x 10(6) M-1.s-1, and for monophasic assembly the rate constant is 2.12(+/- 0.56) x 10(7) M-1.s-1. The microtubule number concentration is constant during elongation of microtubules for biphasic and monophasic assembly.

Breakdown and reassociation of bacterial spinae

1982 ◽  
Vol 28 (7) ◽  
pp. 795-808
Author(s):  
K. B. Easterbrook ◽  
R. W. Coombs
Keyword(s):  
Ionic Strength ◽  
Protein Conformation ◽  
High Ionic Strength ◽  
Random Coil ◽  
Temperature Dependent ◽  
Calcium Effect ◽  
Α Helix ◽  
Low Ionic Strength ◽  
Β Sheet ◽  
Polymeric Structures

The tubular appendage, spina (Easterbrook and Coombs. 1976. Can. J. Microbiol. 22: 438–440), dissociates most efficiently under conditions of low ionic strength (0.01 M), high pH (10), and high temperature (95 °C). The protomer, spinin, thus produced is stable under these conditions and reassociates on cooling to give two distinct filamentous polymeric structures that differ in their stability, protein conformation, and reassociation characteristics. Under conditions of low ionic strength (0.01 M), reassociation is relatively slow and leads to a product that has significant amounts of α-helix in addition to the high β-sheet component; under conditions of high ionic strength (1 M), reassociation is rapid and the non-β-sheet component is in the random coil configuration. Since polymerization of the latter structure is "seeded" by either endogenous or exogenously supplied spina fragments, the protomers comprising it are assumed to be in the same conformation as in the spinae. High ionic strength induces folding of the protomer, multimeric association, and finally, elongation by a temperature-dependent process. Reassociation appears to be pH (6–10) independent and, apart from a possible minor calcium effect, cation nonspecific.

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.

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