Abstract
Observed effects of inorganic phosphate (P(i)) on active isometric muscle may provide the answer to one of the fundamental questions in muscle biophysics: how are the free energies of the chemical species in the myosin- catalyzed ATP hydrolysis (ATPase) reaction coupled to muscle force? Pate and Cooke (1989. Pflugers Arch. 414:73-81) showed that active, isometric muscle force varies logarithmically with [P(i)]. Here, by simultaneously measuring electron paramagnetic resonance and the force of spin-labeled muscle fibers, we show that, in active, isometric muscle, the fraction of myosin heads in any given biochemical state is independent of both [P(i)] and force. These direct observations of mechanochemical coupling in muscle are immediately described by a muscle equation of state containing muscle force as a state variable. These results challenge the conventional assumption mechanochemical coupling is localized to individual myosin heads in muscle.
Original language | English (US) |
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Pages (from-to) | 2657-2664 |
Number of pages | 8 |
Journal | Biophysical journal |
Volume | 77 |
Issue number | 5 |
DOIs | |
State | Published - Nov 1999 |
Bibliographical note
Funding Information:This work was supported by grants from the Muscular Dystrophy Association, the National Institutes of Health (AR32961), the Minnesota Supercomputer Institute, and the National Science Foundation.