scholarly journals Self-association of troponin

1977 ◽  
Vol 167 (1) ◽  
pp. 131-136 ◽  
Author(s):  
S J Lovell ◽  
D J Winzor
Keyword(s):  
Ionic Strength ◽  
Thin Filament ◽  
Velocity Sedimentation ◽  
Troponin Complex ◽  
Self Association

Ox muscle troponin was shown by equilibrium- and velocity-sedimentation studies to undergo concentration-dependent dissociation into its constituent subunits as well as self-association in imidazole buffers, pH 6.9. The extent of troponin association was found to be strongly dependent on ionic strength and also to exhibit a dependence on pH and temperature; under conditions physiological in regard to pH, temperature and ionic strength the extent of polymerization of troponin is considerable in 2 mg/ml solutions. The ability of polymeric troponin to bind to tropomyosin has been inferred from studies of mixtures containing actin-tropomyosin and an excess of troponin over the amount required for the normal 7:1:1 actin-tropomyosin-troponin complex. These findings should be relevant to studies of reconstituted actin-tropomyosin-troponin preparations, since they signify possible chemical as well as physical differences between the gel, paracrystalline and filamentous states of the complex that result from adoption of different preparative procedures for analogues of the native thin filament.

scholarly journals Self-association of α-chymotrypsin at low ionic strength in the vicinity of its pH optimum

1977 ◽  
Vol 161 (3) ◽  
pp. 687-694 ◽  
Author(s):  
R Tellam ◽  
D J Winzor
Keyword(s):  
Ionic Strength ◽  
Electrostatic Interactions ◽  
Sedimentation Equilibrium ◽  
Velocity Sedimentation ◽  
Gel Chromatography ◽  
Ph Optimum ◽  
Equilibrium Sedimentation ◽  
Equilibrium Distributions ◽  
Self Association ◽  
Low Ionic Strength

The self-association of alpha-chymotrypsin and its di-isopropyl phosphoryl derivative in in I0.03 sodium phophate buffer, pH7,9, was investigated by velocity sedimentation, equilibrium sedimentation and difference gel chromatography. No differences between the native and chemically modified enzyme were observed in the ultracentrifuge studies, and only a marginal (0.6%) difference in weight-average elution volume was detected by difference gel chromatography of 5g/litre solutions on Sephadex G-75. From quantitative analyses of sedimentation velocity and sedimentation-equilibrium distributions obtained with iPr2P (di-isopropylphosphoryl)-chymotrypsin, the polymerizing system is postulated to involve an indefinite association of dimer (with an isodesmic association constant of 0.68 litre/g) that is formed by a discrete dimerization step with equilibrium constant 0.25 litre/g. In addition to providing the best fit of the experimental results, this model of chymotrypsin polymerization at low ionic strength is also consistent with an earlier observation that dimer formation is a symmetrical head-to-head phenomenon under conditions of higher ionic strength (I0.29, pH7.9) where association is restricted to a monomer-dimer equilibrium. It is proposed that the dimerization process is essentially unchanged by variation in ionic strength at pH7.9, and that higher polymers are formed by an entirely different mechanism involving largely electrostatic interactions between dimeric species.

Binding of adenylosuccinate synthetase to contractile proteins of muscle

1989 ◽  
Vol 257 (1) ◽  
pp. C29-C35 ◽  
Author(s):  
J. P. Manfredi ◽  
R. Marquetant ◽  
A. D. Magid ◽  
E. W. Holmes
Keyword(s):  
Ionic Strength ◽  
Dissociation Constant ◽  
Thin Filament ◽  
Contractile Proteins ◽  
Purine Nucleotide ◽  
Apparent Dissociation Constant ◽  
Thin Filaments ◽  
Adenylosuccinate Synthetase ◽  
Purine Nucleotide Cycle ◽  
Low Ionic Strength

The muscle isozyme of adenylosuccinate synthetase (AdSS), an enzyme of the purine nucleotide cycle, has previously been shown to bind to purified F-actin in buffers of low ionic strength and pH (Ogawa et al. Eur. J. Biochem. 85: 331-338, 1978). We have extended these observations by measuring the association of both crude and purified AdSS with the contractile proteins of muscle in buffers of physiological ionic strength and pH. Under these conditions, the enzyme binds to F-actin, actin-tropomyosin complexes, reconstructed thin filaments, and myofibrils but not to myosin. The apparent dissociation constant of 1.2 microM and binding maximum of 2.6 nmol enzyme/mg myofibrils indicate that binding of AdSS to myofibrils can be physiologically significant. The results suggest that AdSS in muscle may be associated with the thin filament of myofibrils.

scholarly journals The structure of the native cardiac thin filament at systolic Ca2+ levels

2021 ◽  
Vol 118 (13) ◽  
pp. e2024288118
Author(s):  
Cristina M. Risi ◽  
Ian Pepper ◽  
Betty Belknap ◽  
Maicon Landim-Vieira ◽  
Howard D. White ◽  
...  
Keyword(s):  
Cardiac Muscle ◽  
Binding Sites ◽  
Short Range ◽  
Bound States ◽  
Thin Filament ◽  
Narrow Range ◽  
The Other ◽  
Thin Filaments ◽  
Troponin Complex ◽  
Myosin Binding

Every heartbeat relies on cyclical interactions between myosin thick and actin thin filaments orchestrated by rising and falling Ca2+ levels. Thin filaments are comprised of two actin strands, each harboring equally separated troponin complexes, which bind Ca2+ to move tropomyosin cables away from the myosin binding sites and, thus, activate systolic contraction. Recently, structures of thin filaments obtained at low (pCa ∼9) or high (pCa ∼3) Ca2+ levels revealed the transition between the Ca2+-free and Ca2+-bound states. However, in working cardiac muscle, Ca2+ levels fluctuate at intermediate values between pCa ∼6 and pCa ∼7. The structure of the thin filament at physiological Ca2+ levels is unknown. We used cryoelectron microscopy and statistical analysis to reveal the structure of the cardiac thin filament at systolic pCa = 5.8. We show that the two strands of the thin filament consist of a mixture of regulatory units, which are composed of Ca2+-free, Ca2+-bound, or mixed (e.g., Ca2+ free on one side and Ca2+ bound on the other side) troponin complexes. We traced troponin complex conformations along and across individual thin filaments to directly determine the structural composition of the cardiac native thin filament at systolic Ca2+ levels. We demonstrate that the two thin filament strands are activated stochastically with short-range cooperativity evident only on one of the two strands. Our findings suggest a mechanism by which cardiac muscle is regulated by narrow range Ca2+ fluctuations.

Solution pH That Minimizes Self-Association of Three Monoclonal Antibodies Is Strongly Dependent on Ionic Strength

2012 ◽  
Vol 9 (4) ◽  
pp. 744-751 ◽  
Author(s):  
Shantanu V. Sule ◽  
Jason K. Cheung ◽  
Valentyn Antochshuk ◽  
Amardeep S. Bhalla ◽  
Chakravarthy Narasimhan ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Ionic Strength ◽  
Solution Ph ◽  
Self Association

Physicochemical studies on the aggregation of bovine cardiac tropomyosin with ionic strength

1969 ◽  
Vol 47 (4) ◽  
pp. 411-413 ◽  
Author(s):  
William D. McCubbin ◽  
Cyril M. Kay
Keyword(s):  
Ionic Strength ◽  
High Ionic Strength ◽  
Optical Rotatory Dispersion ◽  
Rotatory Dispersion ◽  
Sedimentation Equilibrium ◽  
Velocity Sedimentation ◽  
Optical Rotatory ◽  
Dispersion Parameters ◽  
Tertiary Structures ◽  
The Individual

The aggregation of bovine cardiac tropomyosin as a function of ionic strength has been studied by the techniques of sedimentation velocity, sedimentation equilibrium, osmometry, viscometry, and optical rotatory dispersion. The measurements indicate that in aqueous buffers at neutral pH and at ionic strengths below 0.6, cardiac tropomyosin is heterogeneous and consists of a monomer in equilibrium with its aggregates. Dissociation of the aggregates occurs on dilution to yield a molecular weight species of approximately 70 000, in very good agreement with the value obtained at high ionic strength. These observations essentially parallel similar findings noted for the polymerization of skeletal tropomyosin, with the exception that the cardiac protein shows no tendency to polymerize at high ionic strength. The virtual constancy of all the optical rotatory dispersion parameters with polymerization suggests that the association is probably linear rather than lateral, with no accompanying changes in secondary and tertiary structures of the individual monomers.

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