1,720,963 research outputs found
Thermodynamic features of myosin filament suspensions: Implications for the modeling of muscle contraction
No full textThe analysis of myosin filament suspensions shows that these solutions are characterized by highly nonideal behavior. From these data a model is constructed that allows us to predict that 1) when subjected to an increasing protein osmotic pressure, myosin filaments experience an elastic deformation, which is not linearly related to the acting force; and 2) at constant protein osmotic pressure, when the cross-bridges of the myosin filaments are subjected to an external, nonosmotic force parallel to the filament axis, they are deformed and the water activity coefficient is altered. As a consequence, in muscle, passive and active shortening of the sarcomere is expected to promote the change of the water-water and of the water-protein interactions. We thus propose to depict muscle contraction as a chemo-osmoelastic transduction, where the analysis of the energy partition during the power stroke requires consideration of the osmotic factor in addition to the chemoelastic ones
On the mechanics of the actin filament: The linear relationship between stiffness and yield strength allows estimation of the yield strength of thin filament in vivo
No full textComparison of the behaviour of actin filaments either modified with tetramethylrhodamine iodoacetamide or decorated with tetramethylrhodamine- phalloidin or with tropomyosin or with myosin subfragment 1 shows that, in all the cases, yield strength is linearly related to stiffness
Reversible inactivation of myosin subfragment-1 activity by mechanical immobilization: A reappraisal
No full textReversible inactivation of myosin subfragment-1 by mechanical immobilization: a reappraisal
A possible solvent effect of adenosine diphosphate influences the binding of ethenoadenosine diphosphate to myosin from skeletal muscle
No full textSkeletal muscle myosin displays two independent and equivalent binding sites for 1,N6 ethenoadenosine diphosphate, with a dissociation constant of 24.7 μM. MgADP, 10 to 40 μM, behaves as a pure competitive type inhibitor (KSI = 8-9 μM) for the binding of 1,N6 ethenoadenosine diphosphate to skeletal muscle myosin. On the contrary, the inhibition by MgADP, 0.11-1.54 mM, is neither competitive nor non-competitive nor mixed, as is revealed by the analysis with the general kinetic equation (K.J. Laidler, P.S. Bunting, The Chemical Kinetics of Enzyme Action, 2nd ed., Clarendon, Oxford, 1973, p. 94). To explain our finding we propose that MgADP operates a complex type of inhibition, acting both directly as a competitor for myosin active sites, and indirectly by perturbing the regions of the solvent near to the protein. © 2001 Elsevier Science B.V
On the stiffness of the natural actin filament decorated with alexa fluor tropomyosin
No full textNatural, phalloidin-free, actin filaments were decorated with tropomyosin made fluorescent by reaction with alexa fluor (R) 488 C5 maleimide. The elastic modulus by stretching of these filaments was then determined and found to span between 38.2 MPa and 61.48 MPa. We tried also to determine the yield strength of the same filaments in the laser light trap operated at 920 mW, the maximum power of the apparatus. Only two out of the 10 filaments tested were broken under these conditions, yield strength being 50.5 and 55 pN, respectively. © 2003 Elsevier Science B.V. All rights reserved
On the elastic properties of tetramethylrhodamine F-actin
No full text(Iodoacetamido)tetramethylrhodamine disrupts F-actin. At the 1:1 fluorophore to actin (as monomer) ratio approximately 80% of the protein becomes non-sedimentable. The fluorescent, non-sedimentable actin copolymerizes with G-actin to yield fluorescent filaments. The tensile strength of these filaments changes with the ratio of the fluorescent non-sedimentable actin to the G-actin, being 1.6 pN, 2.9 pN and 3.6 pN at the 1/4, 2/3 and 1/1 ratios, respectively. These tensile strengths are approximately two orders of magnitude lower than those obtained by decoration of F-actin with phalloidin. © 2001 Elsevier Science B.V. All rights reserved
Effects of chemical modification, tropomyosin and myosin subfragment 1 on the yield strength and critical concentration of F-actin
No full textThe effects of coupling with tetramethylrhodamine-5-iodoacetamide and of the decoration with tropomyosin and with myosin subfragment 1 on the elastic properties of F-actin filament are investigated. At 22 °C, in 15 mM orthophosphate and 3 mM MgCl2, tetramethylrhodamine F-actin displays a yield strength of 3.69 ± 0.213 pN and an elastic modulus by stretching of 0.91 MPa. Decoration with tropomyosin increases the yield strength of tetramethylrhodamine F-actin to 10.51 ± 0.24 pN and the elastic modulus by stretching to 23-75 MPa. Mixtures of myosin subfragment 1 and tetramethylrhodamine F-actin at the 0.2:1, 0.4:1, 0.6:1, 0.8:1, and 1:1 molar ratios are also studied. Both yield strength and the elastic modulus by stretching are found to increase progressively with the ratio. At the 1:1 molar ratio, the yield strength is 15.81 ± 0.26 pN and the elastic modulus by stretching is 13.45 to 40 MPa. Decoration of tetramethylrhodamine F-actin with both tropomyosin and myosin subfragment 1, at the 1:1 molar ratio with the actin monomer, produces filaments with an yield strength of 22.3 ± 0.48 pN
Differential response of fast and slow myosin ATPase from skeletal muscle to F-actin and to phalloidin F-actin
No full textFast muscle myosin responds in similar way to F-actin and to phalloidin F-actin. It is activated 7.5 fold at infinite F-actin concentration and 6.8 fold at infinite phalloidin F-actin. The actomyosin dissociation constants are 0.89±0.34 μM with F-actin and 0.90±0.71 μM with phalloidin F-actin. Slow muscle myosin responds differently to F-actin and to phalloidin F-actin. It is activated 3.76 fold at infinite F-actin concentration and only 2.27 fold at infinite phalloidin F-actin concentration. The actomyosin dissociation constants are 1.95±1.27 μM with F-actin and 0.27±0.16 μM with phalloidin F-actin. At first glance this means that substitution of F-actin with phalloidin F-actin magnifies the difference between fast muscle and slow muscle myosins. Furthermore the change of the dissociation constants may affect the contractile force of the attached crossbridge. © 2002 Elsevier Science B.V. All rights reserved
Anomalous binding of MgADP to myosin of skeletal muscle
No full textBinding of adenosine diphosphate to skeletal muscle myosin was studied using a range of concentrations from 0 to 2 mM. Up to 0.2 mM adenosine diphosphate two equivalent and independent nucleotide binding sites were detected, characterized by the single association constant of 5 x 104 M-1. At greater adenosine diphosphate concentrations a decreasing binding capacity was noticed, bound nucleotide being essentially ~ 0.1 mol/mol at a 1-2 mM adenosine diphosphate concentration. We tentatively propose that nucleotides act indirectly on myosin by promoting the perturbation of the solvent, which is supported by the fact that polyphosphates are known powerful kosmotropes
Dissecting the free energy of formation of the 1:1 actomyosin complex
No full textThe behaviour of solutions of pure myosin, of pure F-actin and of the equimolar mixture of myosin and of F-actin is studied. It is found that the chemical potential of the two proteins, in separate solutions, increases monotonically with the increase of protein osmotic pressure. A method is presented to determine the chemical potential of the 1:1 actin-myosin complex formed from equimolar solutions of myosin and of F-actin (as monomer).This is the first evaluation of the chemical potential of actomyosin under conditions similar to those of skeletal muscle. It is found that the filament suspensions of myosin and of the 1:1 actin-myosin complex display a high non-ideal behavior as well as distinctly different energy profiles as a function of protein osmotic pressure. This supports the hypothesis that, in muscle: (a) detached cross-bridge change significantly their free energy when sarcomere is shifting from the relaxed to the active or to the rigor state; and (b) the cross-bridge attachment-detachment process is accompanied by changes of muscle protein osmotic pressure. Copyright © 2001 Elsevier Science B.V
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