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Effect of ATP depletion on the isolated thick filament of limulus striated muscle
S F Fan1, M M Dewey, D Colflesh
1Department of Anatomical Sciences, State University of New York at Stony Brook 11794.
Insights
Calcium ions enhance internal motions in Limulus muscle thick filaments with ATP. Removing ATP also increases these motions, but with different characteristics, indicating altered filament flexibility.
Area of Science:
- Muscle physiology
- Biophysics
- Molecular biology
Background:
- Calcium ions and ATP are known to influence the internal motions of muscle thick filaments.
- Previous studies have established the role of these factors in muscle contraction dynamics.
Purpose of the Study:
- To investigate the characteristics of high-frequency internal motions in Limulus striated muscle thick filaments under different conditions, specifically with and without ATP and calcium ions.
- To compare the nature of these motions and their dependence on energy supply and specific inhibitors.
Main Methods:
- Dynamic light scattering was employed to measure high-frequency internal motions of isolated thick filaments.
- Electron microscopy and optical diffraction were used to analyze filament structure in ATP-free media.
Main Results:
- Calcium ions, in the presence of ATP, increase high-frequency internal motions of thick filaments.
- Removal of ATP also induces high-frequency internal motions, distinct from calcium-induced motions, and independent of calcium ions.
- These ATP-independent motions are not energy-dependent, are heat-stable, and are insensitive to phenylmethylsulfonyl fluoride, unlike calcium-dependent motions.
- Electron microscopy revealed crossbridges extending from the filament backbone in ATP-free conditions, with optical diffraction lacking crossbridge layer lines.
Conclusions:
- The study reveals two distinct types of high-frequency internal motions in muscle thick filaments: one calcium/ATP-dependent and another ATP-independent.
- The ATP-independent motions are associated with increased filament flexibility and altered crossbridge configuration, suggesting a different regulatory mechanism.
- These findings contribute to understanding the complex mechanical properties and regulation of muscle filaments beyond the canonical actin-myosin interaction.
Abstract:
With the dynamic light scattering method, we have shown that calcium ions increase the high-frequency internal motions of isolated thick filaments of Limulus striated muscle in the presence of ATP (Kubota, K., B. Chu, Shih-fang Fan, M.M. Dewey, P. Brink, and D. Colflesh. J. Mol. Biol. 1983. 166:329 and Fan, S.-f., M.M. Dewey, D. Colflesh, B. Gaylinn, R. Greguski, and B. Chu. Biophys. J. 1985. 47:809). If ATP is removed from the suspending medium, an increase of high-frequency internal motions also has been observed with characteristics different from those of filaments suspended in a medium containing ATP and calcium ions. These internal motions appear whether calcium ions are present or not and are suppressed by trifluoperazine (TFP). The motions differ from the calcium ion-induced motions in that (a) an energy supply is not required; (b) they are insensitive to heat treatment (42 degrees C, 10 min) and (c) they are also insensitive to phenylmethylsulfonyl fluoride which blocks the motions in the presence of ATP and calcium ions (Fan, Shih-fang, M.M. Dewey, D. Colflesh, B. Gaylinn, R. Greguski, and B. Chu. 1985. Biochim. Biophys. Acta. 827:101). Electron micrographs of negatively stained thick filaments in an ATP-free medium show that the majority of crossbridges extend out from the backbone of the filament and optical diffraction patterns from these filaments lack layer lines arising from the crossbridges. The flexibility of the thick filaments suspended in ATP-free media increases.