Structural changes of actin-bound myosin heads after a quick length change in frog skeletal muscle.
Changes in the x-ray diffraction pattern from a frog skeletal muscle were recorded after a quick release or stretch, which was completed within one millisecond, at a time resolution of 0.53 ms using the high-flux beamline at the SPring-8 third-generation synchrotron radiation facility. Reversibility of the effects of the length changes was checked by quickly restoring the muscle length. Intensities of seven reflections were measured. A large, instantaneous intensity drop of a layer line at an axial spacing of 1/10.3 nm(-1) after a quick release and stretch, and its partial recovery by reversal of the length change, indicate a conformational change of myosin heads that are attached to actin. Intensity changes on the 14.5-nm myosin layer line suggest that the attached heads alter their radial mass distribution upon filament sliding. Intensity changes of the myosin reflections at 1/21.5 and 1/7.2 nm(-1) are not readily explained by a simple axial swing of cross-bridges. Intensity changes of the actin-based layer lines at 1/36 and 1/5.9 nm(-1) are not explained by it either, suggesting a structural change in actin molecules.
Yagi
Naoto
N
Japan Synchrotron Radiation Research Institute, SPring-8, Kouto, Sayo-gun, Hyogo. yagi@spring8.or.jp
Iwamoto
Hiroyuki
H
Wakayama
Jun'ichi
J
Inoue
Katsuaki
K
D000199:Actins / Q000737:chemistry* / Q000502:physiology*; D000818:Animals; D003198:Computer Simulation; D066298:In Vitro Techniques; D008954:Models, Biological; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology*; D009218:Myosins / Q000737:chemistry* / Q000502:physiology*; D011485:Protein Binding; D011487:Protein Conformation; D011892:Rana catesbeiana; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000502:physiology; D013314:Stress, Mechanical; D014961:X-Ray Diffraction / Q000379:methods
D000199:Actins; D020409:Molecular Motor Proteins; D009218:Myosins