1,721,135 research outputs found
Is nebulin truly a component of the thin filament
No full textNebulin is a protein coextensive with thin filament in skeletal muscle. Several evidences seem to indicate that nebulin may be a component of the thin filament.
We prepared thin filaments from rabbit and beef skeletal muscle by extraction of myofibrils at high and at low ionic strength. At the end of the purification procedure, nebulin was always found in the fraction containing the thick filaments and was absent from the fraction containing the thin filaments. We propose therefore that, even if nebulin binds to thin filaments, the binding is very week
Mechanic and elastic properties of F-actin
No full textThe mechanic and elastic properties of F-actin were extensively investigated, but, surprising, no attention was paid to the influence of critical concentration on tensile strength. Formally, the critical concentration is the main determinant of the free energy of the monomer-monomer interaction, thus of tensile strength. We have investigated this aspect, the influence of critical concentration on tensile strength, by stretching rhodamnine phalloidin actin filaments by a laser trap. We found that by increasing ionic strength from 3 to 19 mM, critical concentration decreased fron 146 to 36 nM and the yield strength increased from 5.6 to 28.6 pN. At the ionic strength of 12-13 mM, the elastic modulus increased by 330-430 kP/nm up to break point, were it was 38-44.2 MP. Our finding poses the question of how actin filament bears the forces, ie how thin filament supports muscle contraction
Movement impairment : focus on the brain
No full textThe saying “mens sana in corpore sano” has a particular resonance these days because, for the majority who have a very sedentary occupation, the everyday rhythms of life do not compel us to do much physical exercise. Recently published data indicate that exercise can counteract the effects of neurological diseases such as Alzheimer’s disease and have prompted research on the beneficial effects of movement on the brain and brain neurogenesis. This might lead us to hypothesize that the absence or reduction of movements, especially those with antigravity effects, could induce a deterioration of the brain. This Review discusses current knowledge of the relationship between neurogenic capacity and the lack of motor activity in human and animal models
Myofibrils of skeletal muscle : the activity coefficient of orthophosphate
No full textIn the kinetic model of the cross-bridge cycle the rate limiting steps are dependent on the number of cross-bridges in the strongly bound. To analyze the orthophosphate concentration impact we studied the free energy of hydrolysis of ATP in muscle. We determined that at the physiological protein osmotic pressure the orthophosphate showed a classic activity coefficient (0.85) in the myofibrils of skeletal muscle Under the same conditions and at saturation, 2.67 mumoles of orthophosphate are bound per gram of dry myofibrils, with a dissociation constant of 7 x 10(-5) molal. Work is in progress to determine the activity coefficients of adenine nucleotide analogues
Protein crosstalking through osmotic work : the free energy of formation of the MgADP-myosin complexes at the muscle protein osmotic pressure
No full textA method is presented to determine the energy of formation of the myosin-ADP complexes at the muscle protein osmotic pressure. It is found that, at 1.8 x 10^5 dynes/cm^2, the putative protein osmotic pressure in skeletal muscle, the increase of MgADP from 0.05 to 2 mmol, increases the free energy of myosin- ADP and myosin-(ADP)2 by 7.56 x 10^9 and by 9.85 x 10^10 erg/mol, respectively, and decreases the free energy of myosin by 8.34 x 10^10 erg/mol. It is pointed out that the local changes of water chemical potential, induced by the binding of MgADP to myosin, can be sensed by other structures of the contractile machinery, wich per se may even be insensitive to MgADP. Crosstalking between macromolecules can thus be achieved by changes of the water chemical point
Rhodamine phalloidin F-actin : critical concentration versus tensile strength
No full textThe mechanic and elastic properties of rhodamine phalloidin F-actin were investigated as a function of the ionic strength and in the absence of Mg2+. By increasing ionic strength from 3 to 19 mM, critical concentration decreased from 146 to 36 nM and the yield strength increased from 5.6 pN to 28.6 pN. At the ionic strength of 12-13 mM, the elastic modulus by stretching increased by 330-430 kP. nm-1 up to the break point, where it was 38-44.2 MP. The work required to break the filament, 403-439 kJ.M-1 provides an estimate of the free energy of annealing of rhodamine phalloidin F-actin, the annealing constant being 2.8 x 1074 M-1
Rhodamine phalloidin F-actin : critical concentration versus tensile strength
No full textA knowledge of actin's mechanical properties is crucial to understanding its role in motile and cytoskeletal system. It has long been assumed that thin filaments are rigid, however, this view has been challenged in recent years by accurate measurements of filament compliance. We have previously determined tensile strength, elastic modulus and work required to break the filament of phalloidin rhodamine actin be stretching filaments by a laser trap. these experiments have proved that mechanic and elastic properties and actin critical concentration are inversely related and posed the question of how thin filament bears the forces developed in muscle contraction. A solution migth be found in the interaction itself of the cross bridge with the thin filament. We have investigated this aspect by determining the yield strength of thin filament, we have found that myosin subfragment S1 delays the polimerization of F-actin. It is therefore likely that crossbridge attachment decreases the critical concentration of thin filament, by stregthening the interactions of the neighbouring actin monomers
The transition from diffusion to blow-up for a nonlinear Schrodinger equation in dimension 1
No full textWe consider the time-dependent one-dimensional nonlinear Schrodinger equation with a pointwise singular potential. We prove that if the strength of the nonlinear term is small enough, then the solution is well defined for any time, regardless of the choice of initial data; in contrast, if the nonlinearity power is larger than a critical value, for some initial data a blow-up phenomenon occurs in finite time. In particular, if the system is initially prepared in the ground state of the linear part of the Hamiltonian, then we obtain an explicit condition on the parameters for the occurrence of the blow-up
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
