1,720,977 research outputs found
Different Polymeric Forms of Actin Detected by the Fluorescent Probe Terbium Ion
No full textThe interaction of actin [from rabbit skeletal muscle] with Tb3+ was studied by following the fluorescence emitted at 545 nm when the protein was excited at 285 nm in the presence of Tb3+. At low ionic strength, each actin monomer binds, at saturation, 6 Tb3+ with an association constant of 0.8 .mu.M-1. In the presence of 0.1 M KCl the association constant decreases to 0.15 and 0.24 .mu.M-1 at subcritical and overcritical actin concentrations, respectively; the number of the binding sites remains 6. When polymeric actin is formed by the addition of 2 mM MgCl2, the association constant drops to 0.008 .mu.M-1 and the number of the binding sites to 4. The lower number of the Tb3+ binding sites (4) in the actin polymerized by MgCl2 as compared to the number of binding sites (6) of the actin polymerized by KCl is taken as evidence of a looser structure of this latter polymer. Tb3+ does not replace 45Ca2+ at the single, high-affinity site of G-actin. Removal of this Ca2+, in the presence of ..
Mechano-chemical energy transduction in biological systems. The effect of mechanical stimulation on the polymerization of actin: a kinetic study
Full text linkMechanical stimulation (forced circulation in narrow tubing) accelerated the rate of polymerization of [rabbit] actin by as much as 10-fold. The increase in the rate was proportional to the intensity of the stimulation for flow rates between 0-3 cm/s. A statistical factor (the orientation of the flowing particles) is apparently influenced by the flow. Comparison of the kinetics of the polymerization of resting and of mechanically stimulated actin solutions showed that both the nucleation and elongation steps were accelerated. Flow oriented not only the oligomeric structures but also the actin monomers. The elongation reaction, also in the flow-stimulated samples, occurred always by the addition of ATP-G-actin (or ATP-containing oligomers) and not by the fusion of ADP-containing oligomeric structures
The experimental basis of some recent hypotheses on the mechanism of the polymerization of actin: A reappraisal
No full textWe have studied the effect of sonication on the fluorescence of N-(1-pyrenyl)iodoacetamide-labeled F-actin as well as of native actin-pyrenyl-actin mixed oligomers in which the subunits were covalently attached to each other by phenylenebismaleimide. In both cases the fluorescence of the solution was largely decreased by sonication. We have found that this effect is due (a) to a 20-30% decrease of the specific fluorescence of the polymers; (b) to the release of monomers (or other nonfluorescing species) from the polymers. These results question the validity of the novel mechanism for the polymerization of actin recently proposed (D. Pantaloni et al. (1984) J. Biol. Chem. 259, 6274-6283). In these studies, in fact, the implicit assumption was made that the quenching of the fluorescence of the solution under sonication was due exclusively to the conversion of F-actin into G-actin
Cooperative behaviour of the elementary sarcomere units and the cross-bridge step size.
No full textWe present a model of muscle contraction based on purely physical grounds and modulated by a parameter, k, related to the visco-elastic hindrances of the contractile apparatus. The model predicts a strong cooperation among sarcomere units and proposes that viscous hindrance is a fundamental component of the economy of the contraction. The concept of cross-bridge step size is also discussed and it is concluded that the step size is of various and probably undeterminable length. © 2005 Elsevier B.V. All rights reserved
An ADPase from sarcoplasmic reticulum of rabbit muscle cleaves ADP bound to F-actin
No full text1.1. We have found that sarcoplasmic reticulum from rabbit muscle contains an ADPase which cleaves ADP bound to F-actin.
2.2. The interaction is not of the simple Michaelis-Menten type, the order of the reaction being larger than the first.
3.3. A possible explanation of this behaviour could be that ADPase binds to two adjacent actin monomers with a preferred orientation thus cleaving preferentially the nucleotide of one of the two monomers
Characterization of the ATP-G-actin aggregates fomed at low KCl concentration
Full text linkThe ATP-G-actin aggregates formed by incubation of ATP-G-actin in 7.5 mM-KCl were characterized by electron-microscopical observation, by high-pressure liquid chromatography and by the study of the 1,N6-etheno-ATP-ATP exchange reaction between the free and the actin-bound nucleotide. In 30 mM-KCl the initial rate of the reduced-viscosity increase is found to be directly related to the amount of the aggregates formed in the course of the preincubation in 7.5 mM-KCl
The rate-limiting step of the protamine-induced adenosine triphosphatase activity of adenosine triphosphate-G-actin
Full text linkThe release of Pi from the Pi-G-actin-ADP complex is the rate-limiting step in the ATPase activity that is shown by ATP-G-actin in the presence of protamine
Transamidinase of hog kidney II. Isolation of a stable enzyme-amidine complex
No full textNo abstract availabl
Fructose-1,6-bisphosphate Aldolase from Rabbit Muscle. Kinetic Resolution of the Enamine Phosphate from the Enamine-Aldehyde Intermediate at Low Temperature
No full textAt or below −12 °C and in the presence of 40% ethylene glycol, only two out of the four dihydroxyacetone phosphate binding sites of aldolase are catalytically active. At these same temperatures and at pH* 8.3, the equilibrium between the pre-enamine and the enamine plus the post-enamine intermediates is largely shifted in favor of the latter. The enamine phosphate and the enamine-aldehyde phosphate intermediates have been resolved by studying the rate of their formation at −13 °C and pH* 5.28 and the trapping by dl-glyceraldehyde 3-phosphate at −24 °C and pH* 5.24
Actin modifying system of the sarcoplasmic reticulum from rabbit muscle
No full textBy interaction with sarcoplasmic reticulum from rabbit muscle G-actin loses the capability to polymerize. The modification of actin is due to the concomitant action of the Ca2+ ATPase and of an ADPase embedded in the sarcoplasmic reticulum vesicles. Methyl isobutyl xanthine increases the rate of modification of actin by the sarcoplasmic reticulum vesicles by increasing the rate of the exchange of the actin-bound nucleotide
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