Kinetics of the structural transition of muscle thin filaments observed by fluorescence resonance energy transfer.
Fluorescence resonance energy transfer showed that troponin-I changes the position on an actin filament corresponding to three states (relaxed, closed, and open) of the thin filament (Hai et al. (2002) J. Biochem. 131, 407-418). In combination with the stopped-flow method, fluorescence resonance energy transfer between probes attached to position 1, 133, or 181 of troponin-I and Cys-374 of actin on reconstituted thin filaments was measured to follow the transition between three states of the thin filament. When the free Ca(2+) concentration was increased, the transition from relaxed to closed states occurred with a rate constant of approximately 500 s(-1). For the reverse transition, the rate constant was approximately 60 s(-1). When myosin subfragment-1 was dissociated from thin filaments in the presence of Ca(2+) by rapid mixing with ATP, the transition from open to closed states occurred with a single rate constant of approximately 300 s(-1). Light-scattering measurements showed that the ATP-induced myosin subfragment-1 dissociation occurred with a rate constant of approximately 900 s(-1). In the absence of Ca(2+), the transition from open to relaxed states occurred with two rate constants of approximately 400 and approximately 80 s(-1). These transition rates are fast enough to allow the spatial rearrangement of thin filaments to be involved in the regulation mechanism of muscle contraction.
Department of Applied Chemistry and Biotechnology, Fukui University, 3-9-1 Bunkyo, Fukui 910-8507, Japan.
Yuji
Y
Shitaka
Chieko
C
Kimura
Takayoshi
T
Iio
Masao
M
Miki
D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004735:Energy Transfer; D007700:Kinetics; D015335:Molecular Probes; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000502:physiology; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D019210:Troponin I / Q000378:metabolism*
D000199:Actins; D015335:Molecular Probes; D019210:Troponin I; D000255:Adenosine Triphosphate; D002118:Calcium