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. 1999 Nov;77(5):2657–2664. doi: 10.1016/S0006-3495(99)77100-6

Mechanochemical coupling in spin-labeled, active, isometric muscle

JE Baker 1, LE LaConte 1, I Brust-Mascher I 1, DD Thomas 1
PMCID: PMC1300540  PMID: 10545366

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?. 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.

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Selected References

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