title: Mechanochemical coupling in spin-labeled, active, isometric muscle.
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.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA. jb@ddt.biochem.umn.edu
authors.forename: J E
authors.initials: JE
authors.lastname: Baker
authors.forename: L E
authors.initials: LE
authors.lastname: LaConte
authors.forename: I
authors.initials: I
authors.lastname: Brust-Mascher
authors.forename: D D
authors.initials: DD
authors.lastname: Thomas
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004578:Electron Spin Resonance Spectroscopy; D009132:Muscles / Q000378:metabolism* / Q000502:physiology; D009218:Myosins / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011817:Rabbits; D013113:Spin Labels
chemical_list: D013113:Spin Labels; D009218:Myosins