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Originally published as Biophys J. BioFAST on January 26, 2007.
doi:10.1529/biophysj.106.101477
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Biophysical Journal 92:2865-2874 (2007)
© 2007 The Biophysical Society

Mechanism of Tension Generation in Muscle: An Analysis of the Forward and Reverse Rate Constants

Julien S. Davis and Neal D. Epstein

Molecular Physiology Section, Laboratory of Molecular Cardiology, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland

Correspondence: Address reprint requests to Julien S. Davis, Tel.: 301-435-5285; E-mail: davisjs{at}nhlbi.nih.gov.

Tension generation in muscle occurs during the attached phase of the ATP-powered cyclic interaction of myosin heads with thin filaments. The transient nature of tension-generating intermediates and the complexity of the mechanochemical cross-bridge cycle have impeded a quantitative description of tension generation. Recent experiments performed under special conditions yielded a sigmoidal dependence of fiber tension on temperature—a unique case that simplifies the system to a two-state transition. We have applied this two-state analysis to kinetic data obtained from biexponential laser temperature-jump tension transients. Here we present the forward and reverse rate constants for de novo tension generation derived from analysis of the kinetics of the fast laser temperature-jump phase {tau}2 (equivalent of the length-jump phase 2slow). The slow phase {tau}3 is temperature-independent indicating coupling to rather than a direct role in, de novo tension generation. Increasing temperature accelerates the forward, and slows the reverse, rate constant for the creation of the tension-generating state. Arrhenius behavior of the forward and anti-Arrhenius behavior of the reverse rate constant is a kinetic signature of multistate multipathway protein-folding reactions. We conclude that locally unfolded tertiary and/or secondary structure of the actomyosin cross-bridge mediates the power stroke.






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Copyright © 2007 by the Biophysical Society.