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.
Shitaka
Yuji
Y
Department of Applied Chemistry and Biotechnology, Fukui University, 3-9-1 Bunkyo, Fukui 910-8507, Japan.
Kimura
Chieko
C
Iio
Takayoshi
T
Miki
Masao
M
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