adenosine-5--o-(3-thiotriphosphate) and magnesium-pyrophosphate
adenosine-5--o-(3-thiotriphosphate) has been researched along with magnesium-pyrophosphate* in 2 studies
Other Studies
2 other study(ies) available for adenosine-5--o-(3-thiotriphosphate) and magnesium-pyrophosphate
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Cross-bridge binding to actin and force generation in skinned fibers of the rabbit psoas muscle in the presence of antibody fragments against the N-terminus of actin.
To assess the significance of the NH2-terminus of actin for cross-bridge action in muscle, skinned fibers of rabbit psoas muscle were equilibrated with Fab fragments of antibodies directed against the first seven N-terminal residues of actin. With the antibody fragment, active force is more inhibited than relaxed fiber stiffness, or stiffness in rigor or in the presence of magnesium pyrophosphate. Inhibition of stiffness in rigor or with magnesium pyrophosphate does not necessarily indicate involvement of the NH2-terminus of actin in strong cross bridge binding to actin but may simply result from the large size of the Fab. At high Fab concentrations, active force is essentially abolished, whereas stiffness is still detectible under all conditions. Thus, complete inhibition of active force apparently is not due to interference with cross-bridge binding to actin but may result from the Fab-mimicking inhibition of the thin filament by Troponin-1 binding to the NH2-terminus of actin at low Ca2+. However, although Troponin-1 is released from the NH2-terminus at high Ca2+, the Fab is not, thus disallowing force generation upon increase in Ca2+. These data are consistent with involvement of the NH2-terminus of actin in both weak cross-bridge binding to actin and Ca2+ regulation of the thin filament. Topics: Actins; Adenosine Triphosphate; Animals; Binding Sites; Biophysical Phenomena; Biophysics; Calcium; Diphosphates; Immunoglobulin Fab Fragments; In Vitro Techniques; Kinetics; Magnesium Compounds; Muscle Contraction; Muscle Fibers, Skeletal; Myosins; Psoas Muscles; Rabbits; Sarcomeres | 1996 |
State-dependent radial elasticity of attached cross-bridges in single skinned fibres of rabbit psoas muscle.
1. In a single skinned fibre of rabbit psoas muscle, upon attachment of cross bridges to actin in the presence of ADP or pyrophosphate (PPi), the separation between the contractile filaments, as determined by equatorial X-ray diffraction, is found to decrease, suggesting that force is generated in the radial direction. 2. The single muscle fibres were subjected to compression by 0-8% of dextran T500. The changes in lattice spacings by dextran compression were compared with changes induced by cross-bridge attachment to actin. Based on this comparison, the magnitude and the direction of the radial force generated by the attached cross-bridges were estimated. The radial cross-bridge force varied with filament separation, and the magnitude of the radial cross-bridge force reached as high as the maximal axial force produced during isometric contraction. 3. One key parameter of the radial elasticity, i.e. the equilibrium spacing where the radial force is zero, was found to depend on the ligand bound to the myosin head. In the presence of ADP, the equilibrium spacing was 36 nm. In the presence of MgPPi the equilibrium spacing shifted to 35 nm and Ca2+ had little effect on the equilibrium spacing. 4. The equilibrium spacing was independent of the fraction of cross-bridges attached to actin. The fraction of cross-bridges attached in rigor was modulated from 100% to close to 0% by adding up to 10 mM of ATP gamma S in the rigor solution. The lattice spacing remained at 38 nm, the equilibrium spacing for nucleotide-free cross-bridges at mu = 170 mM. 5. Radial force generated by cross-bridges in rigor at large lattice spacings (38 nm < or = d10 < or = 46 nm) appeared to vary linearly with lattice spacing. 6. The titration of ATP gamma S to fibres in rigor provided a correlation between the radial stiffness of the nucleotide-free cross-bridges and the equatorial intensities. The relation between the equatorial intensity ratio I11/I10 and radial stiffness appeared to be approximately linear. 7. The fibres under different conditions showed a wide range of radial stiffness, which was not proportional to the apparent axial stiffness of the fibre. If the apparent axial stiffness is a measure of the fraction of cross-bridges bound to actin, it follows that the radial elastic constant is state dependent; or vice versa.(ABSTRACT TRUNCATED AT 400 WORDS) Topics: Adenosine Diphosphate; Adenosine Triphosphate; Animals; Dextrans; Diphosphates; Elasticity; In Vitro Techniques; Ligands; Magnesium Compounds; Muscle Relaxation; Myosins; Osmotic Pressure; Psoas Muscles; Rabbits; X-Ray Diffraction | 1993 |