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This Article Full Text Full Text (PDF) All Versions of this Article: 574/3/877    most recent jphysiol.2006.111708v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kawai, M. Articles by Ishiwata, S. Search for Related Content PubMed PubMed Citation Articles by Kawai, M. Articles by Ishiwata, S. Related Collections Skeletal Muscle and Exercise

¹ Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, IA 52242, USA
² Department of Physics, School of Science and Engineering, Waseda University, Tokyo 169-8555, Japan
³ Medical Biophysics Unit, Institute of Physiology and Pathophysiology, Ruprecht-Karls-Universität, Im Neuenheimer Feld 326, 69120 Heidelberg, Germany

The temperature dependence of sliding velocity, force and the number of cross-bridges was studied on regulated actin filaments (reconstituted thin filaments) when they were placed on heavy meromyosin (HMM) attached to a glass surface. The regulated actin filaments were used because our previous study on muscle fibres demonstrated that the temperature effect was much reduced in the absence of regulatory proteins. A fluorescently labelled thin filament was attached to the gelsolin-coated surface of a polystyrene bead. The bead was trapped by optical tweezers, and HMM–thin filament interaction was performed at 20–35°C to study the temperature dependence of force at the single-molecule level. Our experiments showed that there was a small increase in force with temperature (Q₁₀ = 1.43) and sliding velocity (Q₁₀ = 1.46). The small increase in force was correlated with the small increase in the number of cross-bridges (Q₁₀ = 1.49), and when force was divided by the number of cross-bridges, the result did not depend on the temperature (Q₁₀ = 1.03). These results demonstrate that the force each cross-bridge generates is fixed and independent of temperature. Our additional experiments demonstrate that tropomyosin (Tm) in the presence of troponin (Tn) and Ca²⁺ enhances both force and velocity, and a truncated mutant, 23Tm, diminishes force and velocity. These results are consistent with the hypothesis that Tm in the presence of Tn and Ca²⁺ exerts a positive allosteric effect on actin to make actomyosin linkage more secure so that larger forces can be generated.

(Received 14 April 2006; accepted after revision 16 May 2006; first published online 18 May 2006)
Corresponding author M. Kawai: Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA 52242, USA. Email: masataka-kawai{at}uiowa.edu

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